LVDT measurment with NI 9237, No supported devices

[Tanieta]

Hello everybody,

My task is to measure the displacement using NI 9237 module and the 

cDAQ9184.

After cabling the LVDT sensor to the NI 9237 Module, I ve created a task using 

NI Max. 

My problem is that when trying to set the input Physical Channel it is always empty (No supported devices found), and I didn't understand the main cause of this.

If somebody have an idea about this, I'll be very grateful if you share it with me 🙂

I have attached a capture for this. 

THank you in advance, 

Tania,

[Stephan_D]

Hi Tiana,

it looks like you have selected a signal type, which is not supported out-of-the-box from the NI-9237.

You can try to create a Voltage/Strain/Bridge input task. The module should appear in this case.

You may have to selct another type of signal and scale the measurment value in you application, because the NI-9237 is build for Strain/Bridge measurments and mainly supports this type of input signals.

Stephan

[Henrik_Volkers]

WHat type of LVDT? 

A classical LVDT will need some volt  sine exitation and the output is a sine with a phase change at zero(middle) position.

Or do you have a LVDT with a DC supply and Vdc output? (internal generator and 'lock-in')

You maybe can hack something together to use the 9237 .. (using a signal generator or headphone out of the soundcard 😉 )

but it will be a hack.

Back in the old days bridge-amplifier worked with AC exitation and (most/all?) could be used with LVDTs .. 

[Tanieta]

Hi to all,

Thank you guys (Henrik_Volkers & Stephan_D ) for all your replies.

In fact, I set up the task to be based on Bridge measurements. 😉

Now I have some other questions if you can help please:

* The 1st point: According to the technical specifications of the displacement sensors ( you can find more infos here:  https://www.hbm.com/en/3058/wa-l-inductive-displacement-transducer-plunger/ ), the nominal sensitivy its 80mv/v. And according to the test record provided by the manufacturer is written : sensitivity at 2mm (as the maximum displacement) is 80.01 mv/v at 2.5V as nominal (rated) voltage; then as far as I know the waveform should display a value of 0,01mv/v as a zero signal. However, when I run my VI, it displays a value of 0.1 mv/v as a zero signal, at 2,5 V.

I was really confused... 

* The 2nd point: I am wondering whether the NI 9237 (25mv/v) supports the output range of this sensor or not ?  

* The 3rd point: When I calculated the Sensor needed current for 2,5 Vrms, and an input resistance of 100 Ohm,it is 25mA,  and the maximum current that NI 9237 can outputs is 15mA. 

So I need an external Power source, but is there any limitations for the this ??

* The final point: is that when I loaded the sensor, to the variation of the the signal, it marks a peak variation and it returns to initial zero signal, that I didn't expect !! 

Thank in advance for any help 🙂

Cheers,

Tania,

[Henrik_Volkers]

LVDT sensors don't work with a DC excitation. You need a clean and stable! sine excitation with a frequency in the range of 1kHz to 20kHz (see spec of sensor). The drive current will be much lower, since you drive an inductivity 😉

The T in LVDT stands for transformer... these things don't work with DC 😄

Without some hacks (voltage divider, maybe level shifter) , an additional sine generator and extra LabVIEW software  you can't use the NI 9237 for an LVDT.  (It would be simpler to use the soundcard to read the an LVDT... if you know how this type of sensor works....and know how to program a sync rectifier/lock in in LabVIEW) 

Where do you get this LVDT from?  If it's an old setup, maybe you can harvest the old LVDT signal conditioner?

If you have a new HBM LVDT, have a look at the scout55 or MVD2555 (oh, they still have it... used it 20 years ago, a nice conditioner 🙂 )  or ask HBM if they are willing to change it to one with a DC output.

If the LVDT is placed in old load cell ... get a new loadcell with an resistive bridge ... that would match the NI 9237.

BTW Schaevitz and HBM have DC powered LVDT sensors that include all this signal conditioning and have a easy to use DC output, but again the NI 9237 wouldn't be the DAQ of choice in that case.

[Tanieta]

Hi Henrik_Volkers,

Thank you for your reply...

Till now I didn't get why the NI 9237 isn't useful even in case of DC output !! 

I've tried to look here and there to find a reason, but ... 😕 

Habe you please any further explanations, and I am sorry for these questions 😄

Thank you in advance,

Tania.

[Henrik_Volkers]

Output voltage range of the sensor?

Input voltage range of the 9237?

(and sorry, that is basic spec reading 101...)

[ChanMin]

Really appreciate your opinion and insight. It really helped me. From South Korea, 2020.