Acquire RVDT

[Ayous]

Hi Jay,

That's the point, the valid range (0°-360°) include all the V-shape, so if the ouput signal is y, how can I linearize the V-shape to know if i'm at x1 (°) or x2 (°) (because of the non-linearity) ?

Respectfully,

[Henrik_Volkers]

Don't bother with nonlinearities you haven't measured yourself, with the new system 😉

Make shure you can capture raw data (some periodes of the input and output sine) and post some of them here.

If the output gets close to zero and you know the phase relation of in- and  output, and you find nonlinearities, you can apply some tricks , depending on the signals you get.

most of the old analog demodulators (I assume used to create the diagram shown) can't compete with modern ADCs and FPGA signalprocessing 😄

If you have a scope , hook it up to the sensor (in (also for trigger) and out) and dial the sensor. You will find the region(s)  where the out phase is shifting 180°

but depending on the sensor mechanics (and harmonics in the excitation,...) is not a perfect zero. If that is a problem, a "fit" on a fixed phase sine would be my next test.

Helpful would be known locked excitation, but otherwise it's just some more calculation (FPGA power) (you need to know the system depending phase shift)

[Henrik_Volkers]

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@Ayous wrote:

Hi Jay,

That's the point, the valid range (0°-360°) include all the V-shape, so if the ouput signal is y, how can I linearize the V-shape to know if i'm at x1 (°) or x2 (°) (because of the non-linearity) ?

Respectfully,

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the phase of the signal will tell you

[Jay14159265]

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@Ayous wrote:

Hi Jay,

That's the point, the valid range (0°-360°) include all the V-shape, so if the ouput signal is y, how can I linearize the V-shape to know if i'm at x1 (°) or x2 (°) (because of the non-linearity) ?

Respectfully,

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Well the best way to do is to look at the phase as recommended by Henrik_Volkers. But if you want, you can try cheating it. Try linearizing it with arccos instead of arcsin 🙂 

[santo_13]

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@Ayous wrote:

Hello all,

My company and I are trying to find a replacement solution of the SET cRIO RDK 9316 card, which acquire LVDT and RVDT sensors. Those cards will be no longer available soon so we have to find a good solution.

For LVDT we have no problem using converters, but for RVDT application it's a bit difficult, we can't find converters which converts linearly the 0-360° angle from our sensor to -x to x pts/V... as the RDK 9316 card did (0° -> -30000pts / 360° -> +30000pts for the 9316 RDK card). The converters we tried were not linear and reaches a maximum tension at 180° before returning to their initial value, so we had 0° -> -5V , 180° -> 5V , 360° -> -5V.

Does someone knows how the RVDT signal was demodulated by the 9316 RDK card, or does anyone has already found a replacement solution ?

Respectfully,

Le Meute Simon

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Are you open to alternative signal converter solution?

TE has a few signal converters to output in voltage or current for LVDT/RVDT inputs.

https://www.te.com/en/plp/signal-conditioners/YG2d5.html

[Ayous]

Thanks all for your precious help,

Santo, that was my first idea, I tried with the converters from PM Instrumentation.

They have 2 kinds of demodulators: A/B and A-B/A+B, I tried the two and there is the results I had

Because I don't know how to treat these signals (I don't know how to make them linear from 0° to 360°), I was thinking by acquire the two outputs signals of the RVDT sensor VS1 and VS2 and make the demodulation by myself but I don't know how this is my problem.

If I use my demodulator: I don't understand how I can treat the output signal of the demodulator to make it linear

If I don't use my demodulator, I don't understand how I can treat the two signals VS1/VS2 (three if I acquire the excitation signal) to have a linear signal

Respectfully,

[Henrik_Volkers]

A basic question to the type of RVDT (I only have worked with LVDTs, resolver and a little with servos in the past)

All datasheets of RVDTs I have found so far declaire a angular measuring range that is +-80° max. 

Opposed to resolver (two phase) or servos (3 phase) , that are able to measure absolute full circle.

The datasheet you  have shown mention +- 15° right? Sorry, my french is a bit rusty 😉

So if you need to measure a certain angular range with that RVDT , it's a question of correct mounting.

Like: In mid position, fix the sensor to half range output, if wrong slope turn 180° or swap the wires (not recommended), or in a calibration system with a absolute angle position and traces like you have shown: define and find the mid range points and slopes in the range of interest.

EDIT:  Your RVDT is resolver 🙂  and has 6 or 5 wires to connect to the SET cRIO RDK 9316 ?  So you need to measure 3 channels: Excitation and both sensor coils (maybe sharing one wire).  Demodulation see: page 19 ff in

https://www.st.com/content/dam/specialevents-assets/dc22/pdf/room-2-7-stdevcon22-session-rotational-...

[Ayous]

Hi,

I come back after I make a test platform to try to acquire the RVDT signal with AI and AO cards with a cRIO.

1st problem:

I don't understand how I can create the great excitation with my AO card. I tried like shown below with my FPGA but the results I had when I acquire the VA and VB from my RVDT shows that the excitation isn't good,

This is the FPGA:

The signals I acquire from the RVDT are the red a green one:

Do I miss something to create a good excitation from my FPGA ?

2nd problem:

When I use the excitation from the module I was using before, I have those kinds of signals from the RVDT:

For me, this validate that my excitation signal from the cRIO is not correct.

So, I need to exploit those signal and for this I move my RVDT from 0° to 360° and I find what the module sent me before:

But now I can use the exact signals to seperate the cases and linearize my signal. This is what I have :

I see that for 2 same values of the 2 sawtooth (exemple the 2 lower peaks), the red signal has the opposite phase compared with the excitation signal (blue), so, does anyone know how I could know this opposition of phase ? I tried with the Extract Single Tone information VI
 but i doesn't work, the detected phase is oscillating between -500 and 500°.

I work with DMA, I maybe need to use only one part of the signal from the DMA ?

To summarize:

- I have trouble to generate a 2.5kHz, 7VRMS signal with my AO (NI 9263)

- I have trouble to know the phase difference between my excitation signal (here acquired because generated by the module) and the VA of VB signal from the RVDT (NI 9215)

Respectfully,

[GerdW]

Hi Ayous,

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@Ayous wrote:

To summarize:

- I have trouble to generate a 2.5kHz, 7VRMS signal with my AO (NI 9263)

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How much current (or power) does your RVDT require - and how much current can you provide with your NI9263? Read the datasheets…

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@Ayous wrote:

I see that for 2 same values of the 2 sawtooth (exemple the 2 lower peaks), the red signal has the opposite phase compared with the excitation signal (blue), so, does anyone know how I could know this opposition of phase ?

To summarize:

- I have trouble to know the phase difference between my excitation signal (here acquired because generated by the module) and the VA of VB signal from the RVDT (NI 9215)

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At the "lower peaks" the red signal has a phase of ~180° and ~0° when compared with the excitation. It seems quite easy for me to distinguish both cases…

[Ayous]

Hi GerdW,

Thanks for your fast reply,

I don't know how much current my RVDT need, the only thing I know it's he needs 7VRMS, and from the spec of the NI9263, a +-10V nominal tension is able to create a 7.07VRMS, am I wrong ?

Yes the phase of the red signals is 0° or 180, so my question is, how could I determine it numerically ? I tried with the VI Extract single tone but it seems not working,

Respectfully,