connecting transducer to NI USB 6212

[lyserui]

Hi, am a med student but I have to do some measurements so am new to all this.

I have a transducer http://www.kulite.com/docs/products/XTM-190.pdf which am supposed to connect to an NI USB 6212 .I don't know/cant figure out which pins connect(configurations). Or in other words don't know where to start and I don't want to blow my transducer.

I already have LabVIEW  2011 installed.

Please help, I will  very greatful.

[aputman]

According to the spec sheet, the output wires of the transducer are the green (+) and white (-).  These should be the wires you want to read with your DAQ device (or multimeter, for testing purposes).  The other two wires appear to be the voltage input needed to power the device.  If you are unsure or you are not comfortable with wiring your hardware for fear of "blowing it up", I would recommend calling your local NI rep to speak with someone who can help you with wiring questions. 

[edjones93 · Accepted solution]

Hi,

I think I can explain a little about how to connect this up based on my prior experience with working with similar sensors. Generally Transducers have an input energy as mentioned in the two articles:

http://digital.ni.com/public.nsf/allkb/084702CE98679BB886256CA3006752D7

http://digital.ni.com/public.nsf/allkb/E96DCCBD929EF9E886256C93006D9EC5

This input energy is the what drives the amplifier in a sense and so the voltage output reading highly depends on the input. Therefore you have four wires, two differential connections with which the inputs, we provide 10 VDC and the output we measure with our Data Acquisition device.

I would however refrain from using the USB 6212. It does not have the signal conditioning required to be able to provide any form of accurate measurement with transducers. I would instead have a look at the products described below:

http://www.ni.com/white-paper/14341/en/

I use it for comparison so as to explain the signal conditioning you will need to perform if you chose to continue using the USB-6212. Firstly you would need to measure the voltage being provided to the transducer and then read back the voltage, you then take that mV reading of the transducer output and divide it by the Voltage reading being driven to the transducer. However the USB-6212 cannot drive this particular transducer, the analog voltage output for the USB-6212 has a maximum current output of 2.4mA. The transducer has an input impedance of 650 Ohms, Voltage is 10 so V=IR gives us that we need 15mA which exceeds the USB-6212 AO, therefore you would need an external power supply.

Now you have your actual value, mV/V which will correspond to a somewhat reliable pressure reading. Our voltage range that the transducer outputs is very narrow, the USB-6212 has an absolute accuracy for example, given in the datasheet of 2.7mV, therefore if we were measuring a range of 250 PSI, then we could only really actually see differences in pressure given our output range of 75mV divisible to 25. So I can only ever tell 10 PSI from the next 10 PSI, an alternative would be to use an external amplifier prior to Analog Input however this will induce noise and attenuation and make your measurements less accurate.

All in all, I would recommend using something with the signal conditioning in-built like the 9218. However if you must use the USB-6212:

1. Use an external power supply to provide 10 VDC and 15mA (at least) to the input + and - for the transducer.

2. Read this voltage on the USB-6212 also.

3. Read the voltage output from the output terminals of the transducer as an analog input on the USB-6212. However you may want to add an amplifier into the circuitry to improve precision - at the loss of some accuracy.

4. Take the reading of mV from the transducer output and the reading of Voltage from the external power supply and then divide mV by V to arrive at the unit of interest, mV/V.

5. Knowing your pressure range, you can then calculate pressure assuming your maximum pressure value from the range selected corresponds to 75mV/V.

I hope this clarifies how you can use this setup but I would stress that this is not recommended for such sensors as your measurements cannot be guaranteed to be reliable, accurate or precise.

Best regards,

Ed

[lyserui · Accepted solution]

thanks all for that quick response. I will try it out and let you know my outcome.

Best regards

lyse

[lyserui]

Hi Ed, thanks again for the idea but am stuck again 🙂 ....I am supposed to write a code for y=mx+b for calibration but I think am going the wrong way. I now have X=Voltage 0.00625mV (according to the calculation mV/V==> 75mV/12V)  and Y= 3.5 bar(3500kPa) .attached is my code ,where is the mistake pls help...

[GerdW]

Hi lyserui,

I am supposed to write a code for y=mx+b for calibration

Well, it could be as easy as this:

Btw. you can apply custom scales in DAQmx too! Did you read the DAQmx basics?

After reading the spec sheet: the rated excitation is 10V, so you get 75mV FSO @ 10V!

The math is quite easy: y = 3.5bar/75mV * x + offset (for 10V excitation). You need to measure x (in V) and you need to determine the offset (in bar) when there is no pressure applied on the sensor…

[lyserui]

Hi GerdW,

thanks  for your help. One more question, the X (V) value  is what I read from my  DAQ assistant ?

Best regards

lys

[lyserui]

Hi,

Thanks all for the help.but my USB 6212 did not work so well.I have decided to use NI9205.It works much better than before .I just have one question, is there a possibility for gain control for my outputsignals (verstärkungsregler) apart from defining my range.

Thanks

lys

[GerdW]

Hi lys,

but my USB 6212 did not work so well.

What doesn't "work so well"?

I have decided to use NI9205.It works much better than before

What means "much better"?

is there a possibility for gain control for my outputsignals (verstärkungsregler) apart from defining my range.

Which "output signals"? The NI9205 is an AI/input module!

Where do you define the range?

What is wrong with defining the range? (The ADC in AI modules most often use a gain amplifier with a fiexd set of input ranges - that's why you set the input range for a DAQmx channel.)

[lyserui]

when I connected the USB 6212 with an amplifier ,I  could measure 3v on the input of the amplifier but 14v from the output and the signals had much interference. With my little knowledge of electronic I could not figure it out why ,although all my devices were ok. With the new device ,the periodicity of the sinus signals are more clear(if I can say that)  but the amplitude  keep "Jumping/changing" .My range is till 12V (that's my max from transducer).

And sorry I meant input signals from the NI9205.

I hope you can understand me sorry but am really not that good .Am just trying.(the last test to end my project) :-).