NI 9237 to RVDT R30A

[BAK777]

Dear All,

I'm a new user of NI systems and I really appreciate and need your help.

I want to connect NI 9237 to RVDT R30A ASSY (the input voltage is 3VRMS). However, I have one load cell connected to my NI which needs 10v excitation and I need (or have?) to use 10v for all of the inputs. I talked to a guy in MEASSPEC (the company that we bought our rvdt from them), and he said we can use 10v excitation if our signal conditioner can support 30mA. I searched the datasheet, but I couldn't figure it out what is what! Can you make some clarification for me? Can NI 9237 support this mA?

I appreciate your help if you introduce me to some books or web pages that can help me to improve my understanding of the modules and knowledge of electricity.

Best Regards,

Bardiya

P.S: I'm not sure that I used the correct forum for this question or not. I really appreciate your help.

[cody_a]

The NI 9237 can support a variety of excitation voltages, up to +10V.  However, it's limited to a maximum output power of 150mA.  Power = Voltage*Current = (V^2)/Resistance.  So at 10V excitation, the maximum current you can provide will be 150mW/10V = 15mA.  This is explained on page 16 of the 9237 spec sheet.

Also, the 9237 has a maximum input range of +/- 25 mV/V, but the R30A output (according to this spec sheet from Measurement Specialties) appears to be significantly higher than that limit.

[BAK777]

So, it means that I can use it or I can't?

Thank you so much for your help. I really appreciate it. Thanks.

Bardiya

[BAK777]

I think I understand it right now, and I can't use these two together. Thank you so much. I appreciate it.

[BAK777]

Can someone suggest me a right modules for connecting 3 RVDTs to cRio? Thanks.

[cody_a · Accepted solution]

My first question is why are you using RVDTs?  They have some advantages, but can be difficult to use without specialized hardware.  In case you need a refresher on RVDT technology, take a look at this.  Ideally, if you must use an RVDT for your application, you'd use an RVDT specifc signal conditioning and measurement device such as the NI SCXI-1540.  These devices, unlike the generic analog input and output devices suggested below, have specialized circuitry for dealing with the nuances of RVDT technology.  You can read more about these things here.

RVDTs need an AC excitation source and have an AC output whose amplitude and phase vary linearly with the angular displacement.  So, if you insist on using it in cRIO, since there is no C series LVDT/RVDT/Resolver signal conditioning module, you'll need two separate modules to use this device with cRIO.  One to provide AC excitation and another to measure AC voltage output.

Excitation Module: The spec sheet for this specific RVDT indicates that it ideally needs a 3 Vrms, 10kHz excitation source.  Since Vrms for a sine wave approximately equals 2.8*Vpp of the wave, that means you need a p-p output range of about 8.5 V.  Here are a couple cards that could fit this spec: NI 9263, NI 9269, NI 9264, NI 9260.

Measurement Module: You can use any analog input module here that has enough channels and can sample at a minimum of 20 kS/s (with 10kHz excitation frequency, you're output will also be 10kHz.  To meet the Nyquist sampling criteria you need 2*10kHz = 20kHz sampling rate).  You can find all the analog input C series modules with at least 4 input channels here.

In summary: Use an RVDT specific measurement device if possible.  If that is not possible, explore other displacement measurement technologies that may be easier to use, such as an optical encoder.  If neither of those things are an option, you should be able to use the above listed analog input and output modules to interact with RVDTs from cRIO, though it will take significant software development on your part.

[BAK777]

I appreciate your awesome answer again. Thanks.

Could I use a transistor instead of RVDT? Transistors are much cheaper, and I think with one output from NI 9263, and one input with NI 9203, I can control the transistor for measuring the angle. Am I wrong? I appreciate your help and guidance. Thanks.

Best Regards,

Bardiya

[Cooking_Up_Code]

You are correct that you should be able to use a transistor using the NI 9263 and NI 9203. Would you be using a MOSFET or a BJT and would it work with the measurements for your application? Either way you could use the 9263 to excite the Gate/Base of the transistor and take measurements with the NI 9203.

[BAK777]

Thanks. I made a huge mistake, and I meant potentiometers. I think they work similarly, is that right? What should I be aware of when I want to choose the correct potentiometer beside the range?

I really appreciate your help.

Bardiya

[BAK777]

Also, I appreciate if someone can help me and show me how to calibrate RVDT/LVDT with NI9263 output, and NI9203 analog input. I'll attach the code that I'm written very soon, but it's not working.