How to make an 8mH inductor which can handle 13V peak square wave without saturation

[Peter]

I used to know all this many years ago... how to work out the flux
density, and choose a material which doesn't saturate, but I have long
forgotten!

It needs to be good with a 13V peak square wave, 500Hz.

So we have 13V across 8mH for 1ms, which from v = L (di/dt) yields
1.625A. A quick hack in LTspice confirms this, for the first 5 cycles.
I had a lot of trouble generating a square wave from -13V to +13V :)
so I am not sure what the current waveform will look like when you
switch to -13V when the current flowing is still 1.625A; I suspect it
will not ever exceed 1.625A later though. With a 13V peak sinewave (a
predefined function in LTspice) it looked to be just under 1A, but all
positive which is obviously BS.

The bit I have forgotten is how to calculate the flux density in the
core. I would prefer the whole thing to be something the size of an
RM10 core
https://www.farnell.com/datasheets/528671.pdf
In 3C95 material you have 5500nH/T^2.

A toroid would have less stray flux, and again there is a vast choice.
I have a bag of these from many years ago
https://www.tme.eu/gb/details/tn16_9.6-3f3/ring-ferrites/ferroxcube/tn16-9-6-6-3-3f3/
which with 83 turns would achieve 8mH.

What I don't get is how much current this will carry. 83 turns at 1.6A
is 132 AT which sounds an awful lot. I thus suspect I will need a
bigger core, probably iron.

Looking on Ebay for ready made stuff, 10mH, I see e.g.
https://www.ebay.co.uk/itm/115852064002
but I am instinctively damn sure that won't carry the current.

Another option is some toroidal transformer, and ignore the existing
winding and put more turns on it. Ebay is full of vintage transformers
but most are pretty big.

I was going to wind the TN16 with some turns and see what it does. I
have an HP 3314 pulse generator and a power amp which can output 9V
peak.

The 8mH needs to be +/- 0.3mH. It was determined experimentally using
this amazing thing
https://www.ebay.co.uk/itm/224101042113
but that obviously contains massive magnetics - it weighs about 1kg.

I also have an LCR meter.

I'd be grateful for any suggestions.

[John Larkin]

On Tue, 30 Jan 2024 16:13:41 +0000, Peter

Post by Peter
I used to know all this many years ago... how to work out the flux
density, and choose a material which doesn't saturate, but I have long
forgotten!
It needs to be good with a 13V peak square wave, 500Hz.
So we have 13V across 8mH for 1ms, which from v = L (di/dt) yields
1.625A. A quick hack in LTspice confirms this, for the first 5 cycles.
I had a lot of trouble generating a square wave from -13V to +13V :)
so I am not sure what the current waveform will look like when you
switch to -13V when the current flowing is still 1.625A; I suspect it
will not ever exceed 1.625A later though. With a 13V peak sinewave (a
predefined function in LTspice) it looked to be just under 1A, but all
positive which is obviously BS.
The bit I have forgotten is how to calculate the flux density in the
core. I would prefer the whole thing to be something the size of an
RM10 core
https://www.farnell.com/datasheets/528671.pdf
In 3C95 material you have 5500nH/T^2.
A toroid would have less stray flux, and again there is a vast choice.
I have a bag of these from many years ago
https://www.tme.eu/gb/details/tn16_9.6-3f3/ring-ferrites/ferroxcube/tn16-9-6-6-3-3f3/
which with 83 turns would achieve 8mH.
What I don't get is how much current this will carry. 83 turns at 1.6A
is 132 AT which sounds an awful lot. I thus suspect I will need a
bigger core, probably iron.
Looking on Ebay for ready made stuff, 10mH, I see e.g.
https://www.ebay.co.uk/itm/115852064002
but I am instinctively damn sure that won't carry the current.
Another option is some toroidal transformer, and ignore the existing
winding and put more turns on it. Ebay is full of vintage transformers
but most are pretty big.
I was going to wind the TN16 with some turns and see what it does. I
have an HP 3314 pulse generator and a power amp which can output 9V
peak.
The 8mH needs to be +/- 0.3mH. It was determined experimentally using
this amazing thing
https://www.ebay.co.uk/itm/224101042113
but that obviously contains massive magnetics - it weighs about 1kg.
I also have an LCR meter.
I'd be grateful for any suggestions.

To make a square wave in LT Spice, use a voltage source, right-click
'advanced' and then 'pulse' and set the params to get what looks
right.

Or run a sine wave through a BV block with some equation. That makes
it easy to change the frequency and keep 50% duty cycle.

The easy way to 'design' an inductor is to buy one. Most suppliers
specify L and R and max current and saturation current. Even if you
enjoy winding inductors, a standard part is a good sanity check.

LCR meters usually lie when measuring power inductors.

What's your application?

[Peter]

Post by John Larkin
To make a square wave in LT Spice, use a voltage source, right-click
'advanced' and then 'pulse' and set the params to get what looks
right.
Or run a sine wave through a BV block with some equation. That makes
it easy to change the frequency and keep 50% duty cycle.
The easy way to 'design' an inductor is to buy one. Most suppliers
specify L and R and max current and saturation current. Even if you
enjoy winding inductors, a standard part is a good sanity check.
LCR meters usually lie when measuring power inductors.
What's your application?

It is to reduce the output from an LVDT, by putting this in series
with the input. The reason for reducing the output is a bit obscure...

[john larkin]

On Tue, 30 Jan 2024 20:32:25 +0000, Peter

Post by Peter

Post by John Larkin
To make a square wave in LT Spice, use a voltage source, right-click
'advanced' and then 'pulse' and set the params to get what looks
right.
Or run a sine wave through a BV block with some equation. That makes
it easy to change the frequency and keep 50% duty cycle.
The easy way to 'design' an inductor is to buy one. Most suppliers
specify L and R and max current and saturation current. Even if you
enjoy winding inductors, a standard part is a good sanity check.
LCR meters usually lie when measuring power inductors.
What's your application?

It is to reduce the output from an LVDT, by putting this in series
with the input. The reason for reducing the output is a bit obscure...

We do a lot of LVDT measurement and simulation, usually at higher
frequency but occasionally at 400 Hz.

You could use a step-down transformer instead of a series inductor,
for less phase shift and better linearity and a predictable ratio.
Some little audio transformer.

Ir maybe a resistive voltage divider.

[Anthony William Sloman]

Post by john larkin
On Tue, 30 Jan 2024 20:32:25 +0000, Peter

Post by Peter

Post by John Larkin
To make a square wave in LT Spice, use a voltage source, right-click
'advanced' and then 'pulse' and set the params to get what looks
right.
Or run a sine wave through a BV block with some equation. That makes
it easy to change the frequency and keep 50% duty cycle.
The easy way to 'design' an inductor is to buy one. Most suppliers
specify L and R and max current and saturation current. Even if you
enjoy winding inductors, a standard part is a good sanity check.
LCR meters usually lie when measuring power inductors.
What's your application?

It is to reduce the output from an LVDT, by putting this in series
with the input. The reason for reducing the output is a bit obscure...

John Larkin is right about one thing - the easiest way of reducing the output from an LVDT is with transformer.

Using it to scale down the drive voltage to the LVDT probably makes more sense than using it to scale down the output, if only because the LVDT would run cooler.

An RM10 has a magnetic path length of 44mm

https://www.tdk-electronics.tdk.com/inf/80/db/fer/rm_10.pdf

Your 132A.turns is thus 3000 A.T/metre which is a lot - you don't really want to go above 50A.T/metre.

You might be able save the idea with a huge gap and lots more turns but I doubt it. I wouldn't bother trying even for the most pointy-headed boss.

https://www.tdk-electronics.tdk.com/download/519704/069c210d0363d7b4682d9ff22c2ba503/ferrites-and-accessories-db-130501.pdf

gives all the information.

[Fred Bloggs]

Post by John Larkin
On Tue, 30 Jan 2024 16:13:41 +0000, Peter

Post by Peter
I used to know all this many years ago... how to work out the flux
density, and choose a material which doesn't saturate, but I have long
forgotten!
It needs to be good with a 13V peak square wave, 500Hz.
So we have 13V across 8mH for 1ms, which from v = L (di/dt) yields
1.625A. A quick hack in LTspice confirms this, for the first 5 cycles.
I had a lot of trouble generating a square wave from -13V to +13V :)
so I am not sure what the current waveform will look like when you
switch to -13V when the current flowing is still 1.625A; I suspect it
will not ever exceed 1.625A later though. With a 13V peak sinewave (a
predefined function in LTspice) it looked to be just under 1A, but all
positive which is obviously BS.
The bit I have forgotten is how to calculate the flux density in the
core. I would prefer the whole thing to be something the size of an
RM10 core
https://www.farnell.com/datasheets/528671.pdf
In 3C95 material you have 5500nH/T^2.
A toroid would have less stray flux, and again there is a vast choice.
I have a bag of these from many years ago
https://www.tme.eu/gb/details/tn16_9.6-3f3/ring-ferrites/ferroxcube/tn16-9-6-6-3-3f3/
which with 83 turns would achieve 8mH.
What I don't get is how much current this will carry. 83 turns at 1.6A
is 132 AT which sounds an awful lot. I thus suspect I will need a
bigger core, probably iron.
Looking on Ebay for ready made stuff, 10mH, I see e.g.
https://www.ebay.co.uk/itm/115852064002
but I am instinctively damn sure that won't carry the current.
Another option is some toroidal transformer, and ignore the existing
winding and put more turns on it. Ebay is full of vintage transformers
but most are pretty big.
I was going to wind the TN16 with some turns and see what it does. I
have an HP 3314 pulse generator and a power amp which can output 9V
peak.
The 8mH needs to be +/- 0.3mH. It was determined experimentally using
this amazing thing
https://www.ebay.co.uk/itm/224101042113
but that obviously contains massive magnetics - it weighs about 1kg.
I also have an LCR meter.
I'd be grateful for any suggestions.

To make a square wave in LT Spice, use a voltage source, right-click
'advanced' and then 'pulse' and set the params to get what looks
right.
Or run a sine wave through a BV block with some equation. That makes
it easy to change the frequency and keep 50% duty cycle.
The easy way to 'design' an inductor is to buy one. Most suppliers
specify L and R and max current and saturation current. Even if you
enjoy winding inductors, a standard part is a good sanity check.
LCR meters usually lie when measuring power inductors.
What's your application?

For an ideal inductance the current will in fact ramp up at the V/L rate to Imax, and then ramp down at -V/L rate to exactly I=0. It will keep this up indefinitely. In reality the inductor is not ideal, L is not constant, and energy is expended transitioning the B-H hysteresis loop.

[legg]

On Tue, 30 Jan 2024 16:13:41 +0000, Peter

Post by Peter
I used to know all this many years ago... how to work out the flux
density, and choose a material which doesn't saturate, but I have long
forgotten!

Don't be surprised. It's common to have to brush up on basics, if
you don't use them regularly.

Post by Peter
It needs to be good with a 13V peak square wave, 500Hz.
So we have 13V across 8mH for 1ms, which from v = L (di/dt) yields
1.625A. A quick hack in LTspice confirms this, for the first 5 cycles.
I had a lot of trouble generating a square wave from -13V to +13V :)
so I am not sure what the current waveform will look like when you
switch to -13V when the current flowing is still 1.625A; I suspect it
will not ever exceed 1.625A later though. With a 13V peak sinewave (a
predefined function in LTspice) it looked to be just under 1A, but all
positive which is obviously BS.

Your AC source is seen by the sim to have the polarity of the first
+ pulse. The -pulse that follows can only return mag current to
zero, hence a net +DC can show up in early portions of the sim.
Ad a load to get AC-only current, eventually.

Post by Peter
The bit I have forgotten is how to calculate the flux density in the
core. I would prefer the whole thing to be something the size of an
RM10 core
https://www.farnell.com/datasheets/528671.pdf
In 3C95 material you have 5500nH/T^2.
A toroid would have less stray flux, and again there is a vast choice.
I have a bag of these from many years ago
https://www.tme.eu/gb/details/tn16_9.6-3f3/ring-ferrites/ferroxcube/tn16-9-6-6-3-3f3/
which with 83 turns would achieve 8mH.
What I don't get is how much current this will carry. 83 turns at 1.6A
is 132 AT which sounds an awful lot. I thus suspect I will need a
bigger core, probably iron.

RM10 DC saturation current will depend on turns count and
gap. Saturation flux in ferrite is ~0.33T.

B = u N I / lm

B = flux density in Teslas
u = 4.pi.E-7
N = turns count
I = current in Amps
lm = magnetic path length (or gap width, if present) in meters.


For pulsed DC

deltsB = V T / N Ae

deltaB = flux density change in Teslas
V = applied volts in Volts
T = time in seconds
N = turns count
Ae = cross-sectional area of flux path im meters^2


inductance of gapped structure

L = 4.pi.E-7 N^2 Ae / lg

L = inductance in Henries
N = turns count
Ae = cross-sectional area of flux path im meters^2
lg = gap width in meters

Post by Peter
Looking on Ebay for ready made stuff, 10mH, I see e.g.
https://www.ebay.co.uk/itm/115852064002
but I am instinctively damn sure that won't carry the current.
Another option is some toroidal transformer, and ignore the existing
winding and put more turns on it. Ebay is full of vintage transformers
but most are pretty big.

Solutions will depend on whether or not you intend to use the part
in AC-only, small signal situations, or whether the part is intended
to do some work in a resonant power or filter circuit.

Post by Peter
I was going to wind the TN16 with some turns and see what it does. I
have an HP 3314 pulse generator and a power amp which can output 9V
peak.
The 8mH needs to be +/- 0.3mH. It was determined experimentally using
this amazing thing
https://www.ebay.co.uk/itm/224101042113
but that obviously contains massive magnetics - it weighs about 1kg.
I also have an LCR meter.
I'd be grateful for any suggestions.

Check what's on offer in distributors' catalogs. This will give
you a ball park idea of the size and shape of stuff you'll be
aiming for and may offer a simple solution off the shelf.

RL

[John Larkin]

Post by John Larkin
On Tue, 30 Jan 2024 16:13:41 +0000, Peter

Post by Peter
I used to know all this many years ago... how to work out the flux
density, and choose a material which doesn't saturate, but I have long
forgotten!

Don't be surprised. It's common to have to brush up on basics, if
you don't use them regularly.

Post by Peter
It needs to be good with a 13V peak square wave, 500Hz.
So we have 13V across 8mH for 1ms, which from v = L (di/dt) yields
1.625A. A quick hack in LTspice confirms this, for the first 5 cycles.
I had a lot of trouble generating a square wave from -13V to +13V :)
so I am not sure what the current waveform will look like when you
switch to -13V when the current flowing is still 1.625A; I suspect it
will not ever exceed 1.625A later though. With a 13V peak sinewave (a
predefined function in LTspice) it looked to be just under 1A, but all
positive which is obviously BS.

Your AC source is seen by the sim to have the polarity of the first
+ pulse. The -pulse that follows can only return mag current to
zero, hence a net +DC can show up in early portions of the sim.
Ad a load to get AC-only current, eventually.

Post by Peter
The bit I have forgotten is how to calculate the flux density in the
core. I would prefer the whole thing to be something the size of an
RM10 core
https://www.farnell.com/datasheets/528671.pdf
In 3C95 material you have 5500nH/T^2.
A toroid would have less stray flux, and again there is a vast choice.
I have a bag of these from many years ago
https://www.tme.eu/gb/details/tn16_9.6-3f3/ring-ferrites/ferroxcube/tn16-9-6-6-3-3f3/
which with 83 turns would achieve 8mH.
What I don't get is how much current this will carry. 83 turns at 1.6A
is 132 AT which sounds an awful lot. I thus suspect I will need a
bigger core, probably iron.

RM10 DC saturation current will depend on turns count and
gap. Saturation flux in ferrite is ~0.33T.
B = u N I / lm
B = flux density in Teslas
u = 4.pi.E-7
N = turns count
I = current in Amps
lm = magnetic path length (or gap width, if present) in meters.
For pulsed DC
deltsB = V T / N Ae
deltaB = flux density change in Teslas
V = applied volts in Volts
T = time in seconds
N = turns count
Ae = cross-sectional area of flux path im meters^2
inductance of gapped structure
L = 4.pi.E-7 N^2 Ae / lg
L = inductance in Henries
N = turns count
Ae = cross-sectional area of flux path im meters^2
lg = gap width in meters

Post by Peter
Looking on Ebay for ready made stuff, 10mH, I see e.g.
https://www.ebay.co.uk/itm/115852064002
but I am instinctively damn sure that won't carry the current.
Another option is some toroidal transformer, and ignore the existing
winding and put more turns on it. Ebay is full of vintage transformers
but most are pretty big.

Solutions will depend on whether or not you intend to use the part
in AC-only, small signal situations, or whether the part is intended
to do some work in a resonant power or filter circuit.

Post by Peter
I was going to wind the TN16 with some turns and see what it does. I
have an HP 3314 pulse generator and a power amp which can output 9V
peak.
The 8mH needs to be +/- 0.3mH. It was determined experimentally using
this amazing thing
https://www.ebay.co.uk/itm/224101042113
but that obviously contains massive magnetics - it weighs about 1kg.
I also have an LCR meter.
I'd be grateful for any suggestions.

Check what's on offer in distributors' catalogs. This will give
you a ball park idea of the size and shape of stuff you'll be
aiming for and may offer a simple solution off the shelf.
RL

It is unusual to run a square wave into an LVDT. If the source is a
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

[Anthony William Sloman]

<snip>

It is unusual to run a square wave into an LVDT. If the source is a too-big square wave, a simple circuit would shape it into the

appropriate amplitude sine. Two or three parts.

It's not so much unusual as downright bonkers.

When I was a young and non-too-well-informed graduate student I excited an LVDT with a triangular wave (which contains the same odd harmonics, but at least their amplitude drops off faster with frequency). The next time I had to excite an LVDT, some ten years later, I used a Baxandall class D oscillator to make a slightly dirty sine wave (about 5% harmonic content) and the time after that - another ten years later - I invented my current mirror variant of the Baxandall class D oscillator to produce an order of magnitude cleaner sine wave.

http://sophia-electronica.com/BillsBaxandall.html

[legg]

On Wed, 31 Jan 2024 09:04:20 -0800, John Larkin <***@997PotHill.com>
wrote:


<snip>

Post by John Larkin
It is unusual to run a square wave into an LVDT. If the source is a
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

RL

[Peter]

Post by legg

Post by John Larkin
It is unusual to run a square wave into an LVDT. If the source is a
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

It is an instrument which contains an LVDT bent into a half circle, to
return an angle.

It is excited with 500Hz, and it is pretty well a square wave. I
didn't design that bit :) And the output is too high, for reasons too
complex to explain. So I need to reduce the output somehow.

[legg]

On Thu, 01 Feb 2024 15:37:48 +0000, Peter

Post by Peter

Post by legg

Post by John Larkin
It is unusual to run a square wave into an LVDT. If the source is a
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

It is an instrument which contains an LVDT bent into a half circle, to
return an angle.
It is excited with 500Hz, and it is pretty well a square wave. I
didn't design that bit :) And the output is too high, for reasons too
complex to explain. So I need to reduce the output somehow.

So you've got 500Hz @ 13V (pk?). and you can't adjust the
source (why not?)

AC or DC?


You could reduce the output phase width with a saturable
reactor.

For pulsating DC, it might be a regulated 'set' reactor.

For AC, it could be a bit more complicated, unless
you were satisfied with just a fixed PW blocker.
That might drift a bit with load or temperature.
Gets physically bigger the more voltseconds you want
to block, for the same current.

The 'complicated' saturable reactor for AC begins to
look like a mag amp.

RL

[Bill Sloman]

Post by Peter

Post by legg

Post by John Larkin
It is unusual to run a square wave into an LVDT. If the source is a
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

It is an instrument which contains an LVDT bent into a half circle, to
return an angle.
It is excited with 500Hz, and it is pretty well a square wave. I
didn't design that bit :) And the output is too high, for reasons too
complex to explain. So I need to reduce the output somehow.

It would make more sense to excite it with a lower amplitude sine wave.
The angle sensing differential transformer will run cooler - those
higher harmonics generate extra heat in the core material.

It's a bigger change than your boss had in mind, but would give you an
appreciably better system.

[legg]

On Thu, 01 Feb 2024 15:37:48 +0000, Peter

Post by Peter

Post by legg

Post by John Larkin
It is unusual to run a square wave into an LVDT. If the source is a
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

It is an instrument which contains an LVDT bent into a half circle, to
return an angle.
It is excited with 500Hz, and it is pretty well a square wave. I
didn't design that bit :) And the output is too high, for reasons too
complex to explain. So I need to reduce the output somehow.

About LVDTs, I know nada.

RL

[John Larkin]

Post by legg
On Thu, 01 Feb 2024 15:37:48 +0000, Peter

Post by Peter

Post by legg

Post by John Larkin
It is unusual to run a square wave into an LVDT. If the source is a
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

It is an instrument which contains an LVDT bent into a half circle, to
return an angle.
It is excited with 500Hz, and it is pretty well a square wave. I
didn't design that bit :) And the output is too high, for reasons too
complex to explain. So I need to reduce the output somehow.

About LVDTs, I know nada.
RL

They can be interesting.

https://en.wikipedia.org/wiki/Linear_variable_differential_transformer

but there are many varieties and most are not well documented. I get
them and test them to understand them better. I recently bought some
from ebay, the kind that are used in machine tools, with micro-inch
resolution.

I'm planning another LVDT/synchro measurement/simulation box and maybe
machine tools could be a new market. For some reason the LVDTs and
synchros used in machining run at much higher frequencies than the
aerospace stuff, maybe because the cables are typically shorter.

There are LVDT-based inclinometers too.

[Anthony William Sloman]

<snip>

Post by John Larkin
They can be interesting.
https://en.wikipedia.org/wiki/Linear_variable_differential_transformer

It's not a great write up. It talks about the high permeability moving core which changes the coupling between the primary and the two opposing secondaries. then goes on to say that they can be used at high temperatures when the moving core isn't necessarily going to be ferromagnetic any longer

https://en.wikipedia.org/wiki/Curie_temperature

Post by John Larkin
but there are many varieties and most are not well documented. I get
them and test them to understand them better. I recently bought some
from ebay, the kind that are used in machine tools, with micro-inch
resolution.

They don't have any built-in resolution. They provide a strictly analog representation of displacement.

The machine tools at Cambridge Instruments mostly used Heidenhain optical Moire-fringe displacement transducers - the foreman had a Sony displacement transducer on his lathe which kept track of the alternation magnetic field impressed on a length of hard ferromagnetic wire, which didn't get messed up by splashes of cutting fluid.

We used that to monitor where the moving stage of our electron beam tester was - the software guys liked its data interface better.

Post by John Larkin
I'm planning another LVDT/synchro measurement/simulation box and maybe
machine tools could be a new market. For some reason the LVDTs and
synchros used in machining run at much higher frequencies than the
aerospace stuff, maybe because the cables are typically shorter.
There are LVDT-based inclinometers too.

Aerospace is fixated on 400Hz - it's their 50/60Hz household A/C.

If you used a ferrite moving core with a fairly high DC resistance you can use higher excitation frequencies without heating the moving core and making it expand.

The LVDT we used in our GaAs crystal puller used to move a bit as it warmed up, until I dropped the excitation amplitude when I reworked the electronics that excited it and extracted the signal.

[legg]

Post by John Larkin

Post by legg
On Thu, 01 Feb 2024 15:37:48 +0000, Peter

Post by Peter

Post by legg

Post by John Larkin
It is unusual to run a square wave into an LVDT. If the source is a
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

It is an instrument which contains an LVDT bent into a half circle, to
return an angle.
It is excited with 500Hz, and it is pretty well a square wave. I
didn't design that bit :) And the output is too high, for reasons too
complex to explain. So I need to reduce the output somehow.

About LVDTs, I know nada.
RL

They can be interesting.
https://en.wikipedia.org/wiki/Linear_variable_differential_transformer
but there are many varieties and most are not well documented. I get
them and test them to understand them better. I recently bought some
from ebay, the kind that are used in machine tools, with micro-inch
resolution.
I'm planning another LVDT/synchro measurement/simulation box and maybe
machine tools could be a new market. For some reason the LVDTs and
synchros used in machining run at much higher frequencies than the
aerospace stuff, maybe because the cables are typically shorter.
There are LVDT-based inclinometers too.

Yeah, there are a host of things I could fiddle with, but I like
to keep my distractions at least vaguely on track.

RL

[Jan Panteltje]

On a sunny day (Fri, 02 Feb 2024 10:08:46 -0500) it happened legg

Post by legg
On Thu, 01 Feb 2024 15:37:48 +0000, Peter

Post by Peter

Post by legg

Post by John Larkin
It is unusual to run a square wave into an LVDT. If the source is a
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

It is an instrument which contains an LVDT bent into a half circle, to
return an angle.
It is excited with 500Hz, and it is pretty well a square wave. I
didn't design that bit :) And the output is too high, for reasons too
complex to explain. So I need to reduce the output somehow.

About LVDTs, I know nada.

Same here,
but reducing he output of a square wave is simple by adding some series diodes..

[whit3rd]

Post by Jan Panteltje
On a sunny day (Fri, 02 Feb 2024 10:08:46 -0500) it happened legg

Post by legg
On Thu, 01 Feb 2024 15:37:48 +0000, Peter

Post by Peter

Post by legg

Post by John Larkin
It is unusual to run a square wave into an LVDT. If the source is a
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

It is an instrument which contains an LVDT bent into a half circle, to
return an angle.
It is excited with 500Hz, and it is pretty well a square wave. I
didn't design that bit :) And the output is too high, for reasons too
complex to explain. So I need to reduce the output somehow.

About LVDTs, I know nada.

Same here,
but reducing he output of a square wave is simple by adding some series diodes..

Not so! That's an inductor being driven, the diodes will cause flyback voltage excursions unless you're
doing them in back-to-back antiparallel pairs.

[Jan Panteltje]

On a sunny day (Fri, 2 Feb 2024 22:38:31 -0800 (PST)) it happened whit3rd

On Friday, February 2, 2024 at 9:59:46 PM UTC-8, Jan Panteltje wrot=

Post by Jan Panteltje
On a sunny day (Fri, 02 Feb 2024 10:08:46 -0500) it happened legg

Post by legg
On Thu, 01 Feb 2024 15:37:48 +0000, Peter

Post by legg

It is unusual to run a square wave into an LVDT. If the source is a=
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

It is an instrument which contains an LVDT bent into a half circle, to=
return an angle.
It is excited with 500Hz, and it is pretty well a square wave. I
didn't design that bit :) And the output is too high, for reasons too=
complex to explain. So I need to reduce the output somehow.

About LVDTs, I know nada.

Same here,
but reducing he output of a square wave is simple by adding some series d=

iodes..
Not so! That's an inductor being driven, the diodes will cause flyback vo=
ltage excursions unless you're
doing them in back-to-back antiparallel pairs.

Yes of course 2 anti parallel.

[Jan Panteltje]

On a sunny day (Sat, 03 Feb 2024 10:45:19 GMT) it happened Jan Panteltje

Post by Jan Panteltje
On a sunny day (Fri, 2 Feb 2024 22:38:31 -0800 (PST)) it happened whit3rd

On Friday, February 2, 2024 at 9:59:46 PM UTC-8, Jan Panteltje wrot=

Post by Jan Panteltje
On a sunny day (Fri, 02 Feb 2024 10:08:46 -0500) it happened legg

Post by legg
On Thu, 01 Feb 2024 15:37:48 +0000, Peter

Post by legg

It is unusual to run a square wave into an LVDT. If the source is a=
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

It is an instrument which contains an LVDT bent into a half circle, to=
return an angle.
It is excited with 500Hz, and it is pretty well a square wave. I
didn't design that bit :) And the output is too high, for reasons too=
complex to explain. So I need to reduce the output somehow.

About LVDTs, I know nada.

Same here,
but reducing he output of a square wave is simple by adding some series d=

iodes..
Not so! That's an inductor being driven, the diodes will cause flyback vo=
ltage excursions unless you're
doing them in back-to-back antiparallel pairs.

Yes of course 2 anti parallel.

But only if on the primary driving the inductor.
The output square wave can just be dropped by diodes
or even a resistor divider
You could even use a bridge recifier and use the DC level in a capacitor.
Or does that setop look for phase?
Then you can still use the zero crossings!
One transistor input into base via resistor,
s diode to protect against reverse Vbe..
We need to know more about the setup.

[Jan Panteltje]

On a sunny day (Sat, 03 Feb 2024 11:02:39 GMT) it happened Jan Panteltje

Post by Jan Panteltje
On a sunny day (Sat, 03 Feb 2024 10:45:19 GMT) it happened Jan Panteltje

Post by Jan Panteltje
On a sunny day (Fri, 2 Feb 2024 22:38:31 -0800 (PST)) it happened whit3rd

On Friday, February 2, 2024 at 9:59:46 PM UTC-8, Jan Panteltje wrot=

Post by Jan Panteltje
On a sunny day (Fri, 02 Feb 2024 10:08:46 -0500) it happened legg

Post by legg
On Thu, 01 Feb 2024 15:37:48 +0000, Peter

Post by legg

It is unusual to run a square wave into an LVDT. If the source is a=
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

It is an instrument which contains an LVDT bent into a half circle, to=
return an angle.
It is excited with 500Hz, and it is pretty well a square wave. I
didn't design that bit :) And the output is too high, for reasons too=
complex to explain. So I need to reduce the output somehow.

About LVDTs, I know nada.

Same here,
but reducing he output of a square wave is simple by adding some series d=

iodes..
Not so! That's an inductor being driven, the diodes will cause flyback vo=
ltage excursions unless you're
doing them in back-to-back antiparallel pairs.

Yes of course 2 anti parallel.

But only if on the primary driving the inductor.
The output square wave can just be dropped by diodes
or even a resistor divider
You could even use a bridge recifier and use the DC level in a capacitor.
Or does that setop look for phase?
Then you can still use the zero crossings!
One transistor input into base via resistor,
s diode to protect against reverse Vbe..
We need to know more about the setup.

PS
you could use a simple bridge rectifier in series with the drive coil
short the + and - output and use the AC input terminals.
One or more bridges in series like that too.

[Bill Sloman]

Post by Jan Panteltje
On a sunny day (Sat, 03 Feb 2024 11:02:39 GMT) it happened Jan Panteltje

Post by Jan Panteltje
On a sunny day (Sat, 03 Feb 2024 10:45:19 GMT) it happened Jan Panteltje

Post by Jan Panteltje
On a sunny day (Fri, 2 Feb 2024 22:38:31 -0800 (PST)) it happened whit3rd

On Friday, February 2, 2024 at 9:59:46 PM UTC-8, Jan Panteltje wrot=

Post by Jan Panteltje
On a sunny day (Fri, 02 Feb 2024 10:08:46 -0500) it happened legg

you could use a simple bridge rectifier in series with the drive coil
short the + and - output and use the AC input terminals.
One or more bridges in series like that too.

It's not a good idea to excite an LVDT with a square wave.
The OP should set up a circuit to provide a stable sine wave of the
right amplitude, rather than waste time trying to cut down the amplitude
of the square wave with temperature dependent voltage drops through diodes.

[whit3rd]

Post by Bill Sloman
It's not a good idea to excite an LVDT with a square wave.
The OP should set up a circuit to provide a stable sine wave of the
right amplitude, rather than waste time trying to cut down the amplitude
of the square wave with temperature dependent voltage drops through diodes.

Just to elaborate: an ideal drive for an LVDT would include a transformer coupling
with a grounded center-tap. You want inductive coupling, any capacitive effect
is distortion, so low voltage/high current is best, and the high harmonics
of a square wave put more current through a capacitor than the fundamental.

In the old days, an IF strip (three inductor/capacitor cans) was a good
and convenient sort of square-to-sine filter. Those aren't easy to
buy this week. If 450 kHz works, there's some ceramic filters
still on the market.

[John Larkin]

Post by whit3rd

Post by Bill Sloman
It's not a good idea to excite an LVDT with a square wave.
The OP should set up a circuit to provide a stable sine wave of the
right amplitude, rather than waste time trying to cut down the amplitude
of the square wave with temperature dependent voltage drops through diodes.

Just to elaborate: an ideal drive for an LVDT would include a transformer coupling
with a grounded center-tap. You want inductive coupling, any capacitive effect
is distortion, so low voltage/high current is best, and the high harmonics
of a square wave put more current through a capacitor than the fundamental.
In the old days, an IF strip (three inductor/capacitor cans) was a good
and convenient sort of square-to-sine filter. Those aren't easy to
buy this week. If 450 kHz works, there's some ceramic filters
still on the market.

LVDTs most always work in the audio range. Aircraft types might run at
a KHz or two, and the ones used on machine tools at 10K maybe.

LVDTs are high impedance sources and cable capacitance can be a
serious problem. So long runs encourage low frequencies.

[John Larkin]

Post by Jan Panteltje
On a sunny day (Sat, 03 Feb 2024 10:45:19 GMT) it happened Jan Panteltje

Post by Jan Panteltje
On a sunny day (Fri, 2 Feb 2024 22:38:31 -0800 (PST)) it happened whit3rd

On Friday, February 2, 2024 at 9:59:46 PM UTC-8, Jan Panteltje wrot=

Post by Jan Panteltje
On a sunny day (Fri, 02 Feb 2024 10:08:46 -0500) it happened legg

Post by legg
On Thu, 01 Feb 2024 15:37:48 +0000, Peter

Post by legg

It is unusual to run a square wave into an LVDT. If the source is a=
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

It is an instrument which contains an LVDT bent into a half circle, to=
return an angle.
It is excited with 500Hz, and it is pretty well a square wave. I
didn't design that bit :) And the output is too high, for reasons too=
complex to explain. So I need to reduce the output somehow.

About LVDTs, I know nada.

Same here,
but reducing he output of a square wave is simple by adding some series d=

iodes..
Not so! That's an inductor being driven, the diodes will cause flyback vo=
ltage excursions unless you're
doing them in back-to-back antiparallel pairs.

Yes of course 2 anti parallel.

But only if on the primary driving the inductor.
The output square wave can just be dropped by diodes
or even a resistor divider
You could even use a bridge recifier and use the DC level in a capacitor.
Or does that setop look for phase?
Then you can still use the zero crossings!
One transistor input into base via resistor,
s diode to protect against reverse Vbe..
We need to know more about the setup.

LVDTs usually use sine wave excitation and a phase-sensitive detector
to convert the signal output into a signed position. The output of an
LVDT is typically zero at the center position. We do most of that
digitally.

There are various LVDT types, too.

One of my manuals has some examples:

http://www.highlandtechnology.com/DSS/P545DS.shtml

[Jan Panteltje]

On a sunny day (Sun, 04 Feb 2024 08:26:46 -0800) it happened John Larkin

Post by John Larkin

Post by Jan Panteltje
On a sunny day (Sat, 03 Feb 2024 10:45:19 GMT) it happened Jan Panteltje

Post by Jan Panteltje
On a sunny day (Fri, 2 Feb 2024 22:38:31 -0800 (PST)) it happened whit3rd

On Friday, February 2, 2024 at 9:59:46 PM UTC-8, Jan Panteltje wrot=

Post by Jan Panteltje
On a sunny day (Fri, 02 Feb 2024 10:08:46 -0500) it happened legg

Post by legg
On Thu, 01 Feb 2024 15:37:48 +0000, Peter

Post by legg

It is unusual to run a square wave into an LVDT. If the source is a=
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

It is an instrument which contains an LVDT bent into a half circle, to=
return an angle.
It is excited with 500Hz, and it is pretty well a square wave. I
didn't design that bit :) And the output is too high, for reasons too=
complex to explain. So I need to reduce the output somehow.

About LVDTs, I know nada.

Same here,
but reducing he output of a square wave is simple by adding some series d=

iodes..
Not so! That's an inductor being driven, the diodes will cause flyback vo=
ltage excursions unless you're
doing them in back-to-back antiparallel pairs.

Yes of course 2 anti parallel.

But only if on the primary driving the inductor.
The output square wave can just be dropped by diodes
or even a resistor divider
You could even use a bridge recifier and use the DC level in a capacitor.
Or does that setop look for phase?
Then you can still use the zero crossings!
One transistor input into base via resistor,
s diode to protect against reverse Vbe..
We need to know more about the setup.

LVDTs usually use sine wave excitation and a phase-sensitive detector
to convert the signal output into a signed position. The output of an
LVDT is typically zero at the center position. We do most of that
digitally.
There are various LVDT types, too.
http://www.highlandtechnology.com/DSS/P545DS.shtml

Thank you, manual wants a login with pasword though.

[John Larkin]

Post by Jan Panteltje
On a sunny day (Sun, 04 Feb 2024 08:26:46 -0800) it happened John Larkin

Post by John Larkin

Post by Jan Panteltje
On a sunny day (Sat, 03 Feb 2024 10:45:19 GMT) it happened Jan Panteltje

Post by Jan Panteltje
On a sunny day (Fri, 2 Feb 2024 22:38:31 -0800 (PST)) it happened whit3rd

On Friday, February 2, 2024 at 9:59:46 PM UTC-8, Jan Panteltje wrot=

Post by Jan Panteltje
On a sunny day (Fri, 02 Feb 2024 10:08:46 -0500) it happened legg

Post by legg
On Thu, 01 Feb 2024 15:37:48 +0000, Peter

Post by legg

It is unusual to run a square wave into an LVDT. If the source is a=
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

It is an instrument which contains an LVDT bent into a half circle, to=
return an angle.
It is excited with 500Hz, and it is pretty well a square wave. I
didn't design that bit :) And the output is too high, for reasons too=
complex to explain. So I need to reduce the output somehow.

About LVDTs, I know nada.

Same here,
but reducing he output of a square wave is simple by adding some series d=

iodes..
Not so! That's an inductor being driven, the diodes will cause flyback vo=
ltage excursions unless you're
doing them in back-to-back antiparallel pairs.

Yes of course 2 anti parallel.

But only if on the primary driving the inductor.
The output square wave can just be dropped by diodes
or even a resistor divider
You could even use a bridge recifier and use the DC level in a capacitor.
Or does that setop look for phase?
Then you can still use the zero crossings!
One transistor input into base via resistor,
s diode to protect against reverse Vbe..
We need to know more about the setup.

LVDTs usually use sine wave excitation and a phase-sensitive detector
to convert the signal output into a signed position. The output of an
LVDT is typically zero at the center position. We do most of that
digitally.
There are various LVDT types, too.
http://www.highlandtechnology.com/DSS/P545DS.shtml

Thank you, manual wants a login with pasword though.

They want you to register. You might get a newsletter about once a
year.

[Jan Panteltje]

On a sunny day (Mon, 05 Feb 2024 07:08:16 -0800) it happened John Larkin

Post by John Larkin

Post by Jan Panteltje
On a sunny day (Sun, 04 Feb 2024 08:26:46 -0800) it happened John Larkin

Post by John Larkin

Post by Jan Panteltje
On a sunny day (Sat, 03 Feb 2024 10:45:19 GMT) it happened Jan Panteltje

Post by Jan Panteltje
On a sunny day (Fri, 2 Feb 2024 22:38:31 -0800 (PST)) it happened whit3rd

On Friday, February 2, 2024 at 9:59:46 PM UTC-8, Jan Panteltje wrot=

Post by Jan Panteltje
On a sunny day (Fri, 02 Feb 2024 10:08:46 -0500) it happened legg

Post by legg
On Thu, 01 Feb 2024 15:37:48 +0000, Peter

Post by legg

It is unusual to run a square wave into an LVDT. If the source is a=
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

It is an instrument which contains an LVDT bent into a half circle, to=
return an angle.
It is excited with 500Hz, and it is pretty well a square wave. I
didn't design that bit :) And the output is too high, for reasons too=
complex to explain. So I need to reduce the output somehow.

About LVDTs, I know nada.

Same here,
but reducing he output of a square wave is simple by adding some series d=

iodes..
Not so! That's an inductor being driven, the diodes will cause flyback vo=
ltage excursions unless you're
doing them in back-to-back antiparallel pairs.

Yes of course 2 anti parallel.

But only if on the primary driving the inductor.
The output square wave can just be dropped by diodes
or even a resistor divider
You could even use a bridge recifier and use the DC level in a capacitor.
Or does that setop look for phase?
Then you can still use the zero crossings!
One transistor input into base via resistor,
s diode to protect against reverse Vbe..
We need to know more about the setup.

LVDTs usually use sine wave excitation and a phase-sensitive detector
to convert the signal output into a signed position. The output of an
LVDT is typically zero at the center position. We do most of that
digitally.
There are various LVDT types, too.
http://www.highlandtechnology.com/DSS/P545DS.shtml

Thank you, manual wants a login with pasword though.

They want you to register. You might get a newsletter about once a
year.

Yea, I was thinking adding ***@whitehouse.gov as email with password biden
but do not want to spam anybody.

[john larkin]

Post by Jan Panteltje
On a sunny day (Mon, 05 Feb 2024 07:08:16 -0800) it happened John Larkin

Post by John Larkin

Post by Jan Panteltje
On a sunny day (Sun, 04 Feb 2024 08:26:46 -0800) it happened John Larkin

Post by John Larkin

Post by Jan Panteltje
On a sunny day (Sat, 03 Feb 2024 10:45:19 GMT) it happened Jan Panteltje

Post by Jan Panteltje
On a sunny day (Fri, 2 Feb 2024 22:38:31 -0800 (PST)) it happened whit3rd

On Friday, February 2, 2024 at 9:59:46 PM UTC-8, Jan Panteltje wrot=

Post by Jan Panteltje
On a sunny day (Fri, 02 Feb 2024 10:08:46 -0500) it happened legg

Post by legg
On Thu, 01 Feb 2024 15:37:48 +0000, Peter

Post by legg

It is unusual to run a square wave into an LVDT. If the source is a=
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

It is an instrument which contains an LVDT bent into a half circle, to=
return an angle.
It is excited with 500Hz, and it is pretty well a square wave. I
didn't design that bit :) And the output is too high, for reasons too=
complex to explain. So I need to reduce the output somehow.

About LVDTs, I know nada.

Same here,
but reducing he output of a square wave is simple by adding some series d=

iodes..
Not so! That's an inductor being driven, the diodes will cause flyback vo=
ltage excursions unless you're
doing them in back-to-back antiparallel pairs.

Yes of course 2 anti parallel.

But only if on the primary driving the inductor.
The output square wave can just be dropped by diodes
or even a resistor divider
You could even use a bridge recifier and use the DC level in a capacitor.
Or does that setop look for phase?
Then you can still use the zero crossings!
One transistor input into base via resistor,
s diode to protect against reverse Vbe..
We need to know more about the setup.

LVDTs usually use sine wave excitation and a phase-sensitive detector
to convert the signal output into a signed position. The output of an
LVDT is typically zero at the center position. We do most of that
digitally.
There are various LVDT types, too.
http://www.highlandtechnology.com/DSS/P545DS.shtml

Thank you, manual wants a login with pasword though.

They want you to register. You might get a newsletter about once a
year.

but do not want to spam anybody.

The next tme that Russia or France or Germany wants to invade your
tiny damp country, we'll sit it out.

[Anthony William Sloman]

<snip>

Post by Jan Panteltje
but do not want to spam anybody.

The next time that Russia or France or Germany wants to invade your tiny damp country, we'll sit it out.

Jan lives in the Netherlands. It doesn't have a common border with France or Russia.

The last time Germany invaded the Netherlands was on the 10th May 1940. They'd completed the job by the 17th May 1940. The USA did sit that one out - they didn't enter WW2 until the 7th December 1941 surprise attack on Pearl Harbor by Japanese forces.

The Netherlands was eventually liberated by US and English forces late in1944 and early in 1945. but mainly in the process of gearing up to invade Germany.

My house in Nijmegen was a Canadian battalion headquarters in the last months of 1944. The convent across the road became a field hospital and the house next door was built - after the war - on land that had been used as a temporary cemetery.

[Jan Panteltje]

On a sunny day (Tue, 06 Feb 2024 12:59:43 -0800) it happened john larkin

Post by john larkin

Post by Jan Panteltje
On a sunny day (Mon, 05 Feb 2024 07:08:16 -0800) it happened John Larkin

Post by John Larkin

Post by Jan Panteltje
On a sunny day (Sun, 04 Feb 2024 08:26:46 -0800) it happened John Larkin

Post by John Larkin

Post by Jan Panteltje
On a sunny day (Sat, 03 Feb 2024 10:45:19 GMT) it happened Jan Panteltje

Post by Jan Panteltje
On a sunny day (Fri, 2 Feb 2024 22:38:31 -0800 (PST)) it happened whit3rd

On Friday, February 2, 2024 at 9:59:46 PM UTC-8, Jan Panteltje wrot=

Post by Jan Panteltje
On a sunny day (Fri, 02 Feb 2024 10:08:46 -0500) it happened legg

Post by legg
On Thu, 01 Feb 2024 15:37:48 +0000, Peter

Post by legg

It is unusual to run a square wave into an LVDT. If the source is a=
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

It is an instrument which contains an LVDT bent into a half circle, to=
return an angle.
It is excited with 500Hz, and it is pretty well a square wave. I
didn't design that bit :) And the output is too high, for reasons too=
complex to explain. So I need to reduce the output somehow.

About LVDTs, I know nada.

Same here,
but reducing he output of a square wave is simple by adding some series d=

iodes..
Not so! That's an inductor being driven, the diodes will cause flyback vo=
ltage excursions unless you're
doing them in back-to-back antiparallel pairs.

Yes of course 2 anti parallel.

But only if on the primary driving the inductor.
The output square wave can just be dropped by diodes
or even a resistor divider
You could even use a bridge recifier and use the DC level in a capacitor.
Or does that setop look for phase?
Then you can still use the zero crossings!
One transistor input into base via resistor,
s diode to protect against reverse Vbe..
We need to know more about the setup.

LVDTs usually use sine wave excitation and a phase-sensitive detector
to convert the signal output into a signed position. The output of an
LVDT is typically zero at the center position. We do most of that
digitally.
There are various LVDT types, too.
http://www.highlandtechnology.com/DSS/P545DS.shtml

Thank you, manual wants a login with pasword though.

They want you to register. You might get a newsletter about once a
year.

but do not want to spam anybody.

The next tme that Russia or France or Germany wants to invade your
tiny damp country, we'll sit it out.

Next time? Russia never invaded here.
On the contrary, it helped - in a big way - defeat the Germans in WW2
Freed many people from German concentration camps.

I have the impression US is falling apart, like the Roman empire did a while after
Nero played the fiddle, just like Trump played twitter (now X).

If you think about 'democracy' lemme give the Musk and Twitter case as example:
Musk asked Twitter users to vote if he should take it over.
Majority said 'yes'.
So that did cost him dearly!
If you held a vote on the next transistor model for your new design, all over the country,
do you think it would work for a majority?
You need decision making done by experts, not by some half senile populist creep like biden.
Playing the masses to power your business.. Like biden's war mongering
to burn his people in wars and grab and increase their taxes by producing and giving away weapons
used for creating unrest all over the globe.
Look at what the creep did, like that other demoncrate named Clignon, make war in Europe
cut Russian pipelines to Europe so as to sell your own oil
then put sanctions on our chip export etc etc (our chip tech is way ahead of the US!)
And the masses will be burned in the next war like your people were burned in Vietnam,
in Iraq (no weapons of mass destruction, just war 'business'), in Afghanistan,
WTF do you think you are other than just an aggressive ant heap asking for a more aggressive
other ant heap (and more knowledgeable one) to evaporate what once was a bunch of settlers
stealing from the local US natives.

China, as empire, has a much longer history and is way ahead now of US (that cannot even land on the moon anymore)
in many fields.
A different system,
And now biden causes with all those sanction on China for your own people to pay more for household things
while they hardly have money for housing and food.

I am not so sure about humanity anymore, it seems to be stuck in dogma now
Told you s a while back:
https://www.sciencedaily.com/releases/2024/02/240206144917.htm

Your war machine running on blood:
https://www.songteksten.nl/songteksten/49312/country-joe-the-fish/vietnam.htm

Your nukes may not even work, maybe they forgot how to .........
https://arstechnica.com/space/2024/02/humanitys-most-distant-space-probe-jeopardized-by-computer-glitch/

Maybe a thousand years, or more, after WW3, some of humanity will, after climate is more suitable
recover and dig up your statue of gibberish like in that
planet of the apes movie..





:-)
Or not!
Dinos

[Jasen Betts]

Post by Peter

Post by legg

Post by John Larkin
It is unusual to run a square wave into an LVDT. If the source is a
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.

It is an instrument which contains an LVDT bent into a half circle, to
return an angle.

It sounds kind of like the LVDT wanted to be a resolver.

Post by Peter
It is excited with 500Hz, and it is pretty well a square wave. I
didn't design that bit :) And the output is too high, for reasons too
complex to explain. So I need to reduce the output somehow.

Well that's a shame. You'll have to use a method that's suited to your
application.

[John Larkin]

Post by Anthony William Sloman
<snip>

Post by John Larkin
It is unusual to run a square wave into an LVDT. If the source is a
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.
RL

Subject: Re: How to make an 8mH inductor which can handle 13V peak
square wave without saturation
Date: Tue, 30 Jan 2024 20:32:25 +0000

[legg]

Post by John Larkin

Post by Anthony William Sloman
<snip>

Post by John Larkin
It is unusual to run a square wave into an LVDT. If the source is a
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.
RL

Subject: Re: How to make an 8mH inductor which can handle 13V peak
square wave without saturation
Date: Tue, 30 Jan 2024 20:32:25 +0000

Not on this reader. I have only:

Tue, 30 Jan 2024 16:13:41

RL

[john larkin]

Post by John Larkin

Post by John Larkin

Post by Anthony William Sloman
<snip>

Post by John Larkin
It is unusual to run a square wave into an LVDT. If the source is a
too-big square wave, a simple circuit would shape it into the
appropriate amplitude sine. Two or three parts.

I see no reference to an LVDT application in the Peter's posting.
RL

Subject: Re: How to make an 8mH inductor which can handle 13V peak
square wave without saturation
Date: Tue, 30 Jan 2024 20:32:25 +0000

Tue, 30 Jan 2024 16:13:41
RL

Anyhow, he said he wanted to reduce the drive level into an LVDT.

I think he could use a simple LC or RLC to make a nice lower-amplitude
sine from his big square wave.

[Clive Arthur]

On 01/02/2024 23:17, john larkin wrote:

<snip>

Post by john larkin
Anyhow, he said he wanted to reduce the drive level into an LVDT.
I think he could use a simple LC or RLC to make a nice lower-amplitude
sine from his big square wave.

Depends how the demodulation works, it's often synched to the drive
signal and there may be no phase adjustment.

[John Larkin]

On Fri, 2 Feb 2024 16:20:30 +0000, Clive Arthur

Post by Anthony William Sloman
<snip>

Post by john larkin
Anyhow, he said he wanted to reduce the drive level into an LVDT.
I think he could use a simple LC or RLC to make a nice lower-amplitude
sine from his big square wave.

Depends how the demodulation works, it's often synched to the drive
signal and there may be no phase adjustment.

An RLC can make zero phase shift, or lead or lag. The user would have
to consider that. Maybe the original system assumes square waves!

The problem is underspecified.

[legg]

On Tue, 30 Jan 2024 16:13:41 +0000, Peter

Post by Peter
I used to know all this many years ago... how to work out the flux
density, and choose a material which doesn't saturate, but I have long
forgotten!
It needs to be good with a 13V peak square wave, 500Hz.

<snip>

Post by Peter
core. I would prefer the whole thing to be something the size of an
RM10 core
https://www.farnell.com/datasheets/528671.pdf
In 3C95 material you have 5500nH/T^2.

<snip>

Post by Peter
I have a bag of these from many years ago
https://www.tme.eu/gb/details/tn16_9.6-3f3/ring-ferrites/ferroxcube/tn16-9-6-6-3-3f3/
which with 83 turns would achieve 8mH.
What I don't get is how much current this will carry.

<snip>

Post by Peter
Looking on Ebay for ready made stuff, 10mH, I see e.g.
https://www.ebay.co.uk/itm/115852064002
but I am instinctively damn sure that won't carry the current.

<snip>

Post by Peter
I was going to wind the TN16 with some turns and see what it does. I
have an HP 3314 pulse generator and a power amp which can output 9V
peak.

<snip..

It would be easier to help if you stated the application and known
limits/requirements of size, weight, mounting method, environment etc.

'carry the current' really doesn't tell us anything.

If there are 'found' materials you'd prefer to use . . . and results
from your attempts to do so.

etc.

RL

[Clive Arthur]

On 30/01/2024 16:13, Peter wrote:

<snip>

Post by Peter
A toroid would have less stray flux, and again there is a vast choice.
I have a bag of these from many years ago
https://www.tme.eu/gb/details/tn16_9.6-3f3/ring-ferrites/ferroxcube/tn16-9-6-6-3-3f3/
which with 83 turns would achieve 8mH.

...but nowhere near enough current. Ferroxcube have (or had) a free
downloadable calculator.

As you have already some cores, you could stack several into a tube
shape. I've done this where the available space made it the only game
in town. Tricky to wind but fun, FSVO 'fun'.

[John Larkin]

On Fri, 2 Feb 2024 16:17:45 +0000, Clive Arthur

Post by Anthony William Sloman
<snip>

Post by Peter
A toroid would have less stray flux, and again there is a vast choice.
I have a bag of these from many years ago
https://www.tme.eu/gb/details/tn16_9.6-3f3/ring-ferrites/ferroxcube/tn16-9-6-6-3-3f3/
which with 83 turns would achieve 8mH.

...but nowhere near enough current. Ferroxcube have (or had) a free
downloadable calculator.
As you have already some cores, you could stack several into a tube
shape. I've done this where the available space made it the only game
in town. Tricky to wind but fun, FSVO 'fun'.

An LVDT is not likely to need a lot of excitation current.

[Clive Arthur]

Post by John Larkin
On Fri, 2 Feb 2024 16:17:45 +0000, Clive Arthur

Post by Anthony William Sloman
<snip>

Post by Peter
A toroid would have less stray flux, and again there is a vast choice.
I have a bag of these from many years ago
https://www.tme.eu/gb/details/tn16_9.6-3f3/ring-ferrites/ferroxcube/tn16-9-6-6-3-3f3/
which with 83 turns would achieve 8mH.

...but nowhere near enough current. Ferroxcube have (or had) a free
downloadable calculator.
As you have already some cores, you could stack several into a tube
shape. I've done this where the available space made it the only game
in town. Tricky to wind but fun, FSVO 'fun'.

An LVDT is not likely to need a lot of excitation current.

Probably, but the OP didn't specify the application. LVDTs can be
*very* long - the materials testing machines I worked on often used
short stroke LVDTs for test coupon strain measurement and long stroke -
0.5m - for clamp positioning, but in some applications much longer
devices can be used.

I'm assuming the OP has tried an 8mH inductor, is happy with the result,
and doesn't want any more complication.

[John Larkin]

On Fri, 2 Feb 2024 23:00:29 +0000, Clive Arthur

Post by Clive Arthur

Post by John Larkin
On Fri, 2 Feb 2024 16:17:45 +0000, Clive Arthur

Post by Anthony William Sloman
<snip>

Post by Peter
A toroid would have less stray flux, and again there is a vast choice.
I have a bag of these from many years ago
https://www.tme.eu/gb/details/tn16_9.6-3f3/ring-ferrites/ferroxcube/tn16-9-6-6-3-3f3/
which with 83 turns would achieve 8mH.

...but nowhere near enough current. Ferroxcube have (or had) a free
downloadable calculator.
As you have already some cores, you could stack several into a tube
shape. I've done this where the available space made it the only game
in town. Tricky to wind but fun, FSVO 'fun'.

An LVDT is not likely to need a lot of excitation current.

Probably, but the OP didn't specify the application. LVDTs can be
*very* long - the materials testing machines I worked on often used
short stroke LVDTs for test coupon strain measurement and long stroke -
0.5m - for clamp positioning, but in some applications much longer
devices can be used.
I'm assuming the OP has tried an 8mH inductor, is happy with the result,
and doesn't want any more complication.

Somehow I doubt that. He calculated 1.6 amps of LVDT excitation
current.

[Peter]

Post by John Larkin

Post by Clive Arthur
I'm assuming the OP has tried an 8mH inductor, is happy with the result,
and doesn't want any more complication.

Somehow I doubt that. He calculated 1.6 amps of LVDT excitation
current.

That is exactly what I did.

I bought a 0-10mH (in 1mH steps) variable inductor off Ebay and found
8mH does the perfect job. General Radio 940
https://www.ebay.co.uk/itm/224101042113

Got this from Mouser and will test it
https://www.mouser.co.uk/datasheet/2/54/5700_series-777305.pdf

The 1.6 amps is real, give or take a bit. Yesit surprises me it is
that much. But I can't change the drive circuit. It's simply crap.
Honeywell, BTW ;) Well, actually, from the last days of Bendix King,
around 24 years ago.

[John Larkin]

On Tue, 13 Feb 2024 13:47:06 +0000, Peter

Post by Peter

Post by John Larkin

Post by Clive Arthur
I'm assuming the OP has tried an 8mH inductor, is happy with the result,
and doesn't want any more complication.

Somehow I doubt that. He calculated 1.6 amps of LVDT excitation
current.

That is exactly what I did.
I bought a 0-10mH (in 1mH steps) variable inductor off Ebay and found
8mH does the perfect job. General Radio 940
https://www.ebay.co.uk/itm/224101042113
Got this from Mouser and will test it
https://www.mouser.co.uk/datasheet/2/54/5700_series-777305.pdf
The 1.6 amps is real, give or take a bit. Yesit surprises me it is
that much. But I can't change the drive circuit. It's simply crap.
Honeywell, BTW ;) Well, actually, from the last days of Bendix King,
around 24 years ago.

1.6 amps of square wave into an LVDT is shocking. Maybe the same
person designed the LVDT and the driver.

What does it do? I mean, what mechanical thing does it measure?

[Tauno Voipio]

Post by John Larkin
On Tue, 13 Feb 2024 13:47:06 +0000, Peter

Post by Peter

Post by John Larkin

Post by Clive Arthur
I'm assuming the OP has tried an 8mH inductor, is happy with the result,
and doesn't want any more complication.

Somehow I doubt that. He calculated 1.6 amps of LVDT excitation
current.

That is exactly what I did.
I bought a 0-10mH (in 1mH steps) variable inductor off Ebay and found
8mH does the perfect job. General Radio 940
https://www.ebay.co.uk/itm/224101042113
Got this from Mouser and will test it
https://www.mouser.co.uk/datasheet/2/54/5700_series-777305.pdf
The 1.6 amps is real, give or take a bit. Yesit surprises me it is
that much. But I can't change the drive circuit. It's simply crap.
Honeywell, BTW ;) Well, actually, from the last days of Bendix King,
around 24 years ago.

1.6 amps of square wave into an LVDT is shocking. Maybe the same
person designed the LVDT and the driver.
What does it do? I mean, what mechanical thing does it measure?

The OP's thing may be mis-identified.

It seems that there is an angle transmitter from a piece of avionics.

The usual angle transmitters in avionics are: a three-phase synchro,
a resolver (sine+cosine) and a sine-cosine potentiometer.

The drive level is suspect. An electronic synthetic shaft with two
interconnected synchros can need so much. Another place where a magnetic
core is heavily driven is a flux-valve compass sensor, but it does not
have any moving parts (like the LVDT core).

John is right: What is the thing supposed to achieve?

[Anthony William Sloman]

Post by Tauno Voipio

Post by John Larkin

Post by Peter

Post by Clive Arthur
I'm assuming the OP has tried an 8mH inductor, is happy with the result,
and doesn't want any more complication.

Somehow I doubt that. He calculated 1.6 amps of LVDT excitation current.

That is exactly what I did.
I bought a 0-10mH (in 1mH steps) variable inductor off Ebay and found
8mH does the perfect job. General Radio 940
https://www.ebay.co.uk/itm/224101042113
Got this from Mouser and will test it
https://www.mouser.co.uk/datasheet/2/54/5700_series-777305.pdf
The 1.6 amps is real, give or take a bit. Yesit surprises me it is
that much. But I can't change the drive circuit. It's simply crap.
Honeywell, BTW ;) Well, actually, from the last days of Bendix King,
around 24 years ago.

1.6 amps of square wave into an LVDT is shocking. Maybe the same
person designed the LVDT and the driver.
What does it do? I mean, what mechanical thing does it measure?

The OP's thing may be mis-identified.
It seems that there is an angle transmitter from a piece of avionics.
The usual angle transmitters in avionics are: a three-phase synchro,
a resolver (sine+cosine) and a sine-cosine potentiometer.

Perhaps, but angle sensing variable transformers are real enough.

Post by Tauno Voipio
The drive level is suspect.

24 years ago some people were rather ham-handed.

Post by Tauno Voipio
John is right: What is the thing supposed to achieve?

Always a good question. The answer is probably to get some ancient lump pf rubbish working with the minimum investment of effort.
It's rarely a wise approach, but people under pressure can't afford wisdom.

[Peter]

Post by Anthony William Sloman
Always a good question. The answer is probably to get some ancient lump pf rubbish working with the minimum investment of effort.
It's rarely a wise approach, but people under pressure can't afford wisdom.

It is an artificial horizon called KI256. I need to attenuate the roll
output a bit.

I have the circuits of the driver and circuits of the KI256. I
measured the KI256 LVDT primary inductance, etc.

Some other data points are that another inductor but a small one, just
did nothing and presumably saturated.

Crazy to have such a high drive level; I agree.

[legg]

On Tue, 30 Jan 2024 16:13:41 +0000, Peter

Post by Peter
I used to know all this many years ago... how to work out the flux
density, and choose a material which doesn't saturate, but I have long
forgotten!
It needs to be good with a 13V peak square wave, 500Hz.
So we have 13V across 8mH for 1ms, which from v = L (di/dt) yields
1.625A. A quick hack in LTspice confirms this, for the first 5 cycles.
I had a lot of trouble generating a square wave from -13V to +13V :)
so I am not sure what the current waveform will look like when you
switch to -13V when the current flowing is still 1.625A; I suspect it
will not ever exceed 1.625A later though. With a 13V peak sinewave (a
predefined function in LTspice) it looked to be just under 1A, but all
positive which is obviously BS.
The bit I have forgotten is how to calculate the flux density in the
core. I would prefer the whole thing to be something the size of an
RM10 core
https://www.farnell.com/datasheets/528671.pdf
In 3C95 material you have 5500nH/T^2.
A toroid would have less stray flux, and again there is a vast choice.
I have a bag of these from many years ago
https://www.tme.eu/gb/details/tn16_9.6-3f3/ring-ferrites/ferroxcube/tn16-9-6-6-3-3f3/
which with 83 turns would achieve 8mH.
What I don't get is how much current this will carry. 83 turns at 1.6A
is 132 AT which sounds an awful lot. I thus suspect I will need a
bigger core, probably iron.
Looking on Ebay for ready made stuff, 10mH, I see e.g.
https://www.ebay.co.uk/itm/115852064002
but I am instinctively damn sure that won't carry the current.
Another option is some toroidal transformer, and ignore the existing
winding and put more turns on it. Ebay is full of vintage transformers
but most are pretty big.
I was going to wind the TN16 with some turns and see what it does. I
have an HP 3314 pulse generator and a power amp which can output 9V
peak.
The 8mH needs to be +/- 0.3mH. It was determined experimentally using
this amazing thing
https://www.ebay.co.uk/itm/224101042113
but that obviously contains massive magnetics - it weighs about 1kg.
I also have an LCR meter.
I'd be grateful for any suggestions.

If you can scope a current waveform, you might get an idea of
what the most troublesome harmonics are, then see if a simple
LC filter will help. You'll need the C for any L to work.

RL

[Peter]

Just an update.

I tested that 8mH coil from Mouser. Verified at 8mH with an LCR meter
and with the $500 micro tweezer thingy.

Doesn't work!! It behaves like it was 20mH or something like that. The
attenuation is way too high. But 8mH was the perfect value with that
funny milspec 0-10mH box I got off Ebay, which was heavy enough to
contain pretty big inductors.

So what is happening?

Must be something in the waveform which is buggering up the way these
inductors behave, in conjunction with the demodulation scheme used to
"decode" the LVDT position.

Maybe it is saturating, but saturation has the opposite effect: it
*lowers* the effective inductance.

So I bought a 2.5mH one from Mouser, again one which can do 1.5A or
so, and will try that, after the potting compound has gone off :)

[Bill Sloman]

Post by Peter
Just an update.
I tested that 8mH coil from Mouser. Verified at 8mH with an LCR meter
and with the $500 micro tweezer thingy.
Doesn't work!! It behaves like it was 20mH or something like that. The
attenuation is way too high. But 8mH was the perfect value with that
funny milspec 0-10mH box I got off Ebay, which was heavy enough to
contain pretty big inductors.
So what is happening?
Must be something in the waveform which is buggering up the way these
inductors behave, in conjunction with the demodulation scheme used to
"decode" the LVDT position.

An inductor in series with the excitation coils of an LVDT will shift
the phase of the current going through the LVDT. If the output of the
LVDT is being demodulated with a phase sensitive detector you'd need a
matching shift in the phase of the drive to the demodulator to get a
sensible (or useful) output.

A precision rectifier wouldn't have that problem, but they weren't all
that precise decades ago, and not all that popular. They also don't
reject noise and out-of-phase pick-up, so nobody sensible would have
used one.

Post by Peter
Maybe it is saturating, but saturation has the opposite effect: it
*lowers* the effective inductance.

Worse - it could be saturating on part of the cycle and giving you a
very funny current waveform going through the LVDT - actually a rotary
variable transformer, but we've been through that,

Looking at the current waveforms is always a good idea, but not always
all that easy.

Post by Peter
So I bought a 2.5mH one from Mouser, again one which can do 1.5A or
so, and will try that, after the potting compound has gone off :)

More looking a what's actually going on might be a good idea - buying
random parts before you had worked out exactly why the last one didn't
work isn't good policy.