Getting Started with a Transtek LVDT

[RobertUWM]

Hello,

I am looking for some guidance on how to get human readable results from a transtek 0216-0000 LVDT.

For NI equipment I have a NI cDAQ-9178 with 2 NI9237 and a NI9025.

For the LVDT it is a Trans-tek LVDT 0216-000 with a LVDT signal conditioner series 210-220 oscillator/demodulator.

Here are the data sheets for the LVDT and the signal conditioner

http://www.transtekinc.com/assets/files/Catalog_PDFs_04C/LVDTs/Ser210_220_04c.pdf <- LVDT

http://www.transtekinc.com/assets/files/Catalog_PDFs_04C/Accessories/Ser1000_04c.pdf <- Signal Conditioner

Thank you for your time.

[KateB]

9237 voltage range is much lower than your signal conditioning output voltage. Please consider changing the module, or if you use current output signal conditioning, you should use a module that acquire current.

[RobertUWM]

Any suggestion for what module to use, I would evently like to be able to read up to 3 LVDT with signal conditions off of the same module.

[K_Joy]

Hi Robert UWM,

I assume you meant 9205 for the module you have: https://www.ni.com/en-us/shop/model/ni-9205.html

Your 9237 would only be used if you wanted to plug the LVDT directly into our module. That module is used to measure bridge sensors like the LVDT, but the signal conditioner converts that value to a voltage. To read that voltage, you will use an analog input module like the 9205.

On page 12 of the LVDT spec sheet (the third page, it’s numbered 12) you can see the ranges of that sensor when read through the oscillator/demodulator. It has an output range of +-5VDC. The 9205 has a programmable input range up to +-10VDC, so your readings should be within the range of the 9205.

While the signal conditioner can produce voltages outside of the range of the 9205, the spec sheet for the LVDT tells you that it shouldn’t exceed +-5VDC.

Regards,

Kelsey Johnson

Applications Engineering

National Instruments

[RobertUWM]

Thank you its good to know I can use the equipment I already have.

Any suggestions on what NI-DAQmx global virtual channel I should set up for the LVDT? I think I need something that will take a starting voltage and find the difference between the measured voltage.

For calibration data I was given table of voltages with the corresponding displacements.

[fromm8]

Hello Robert,

If your question is about the kind of task you should create with the "daqmx create virtual channel.vi", you should create an analog input voltage task (AI voltage).

Regards

Frank R.

[RobertUWM]

Thanks Frank R.

From my understanding of LVDTs I would need to grab an initial voltage reading and compare this to samples as they come in and use this difference to determine displacement?

Is my understanding correct? If so how do I go about doing this?

Thank you for your time,

Robert B

[K_Joy]

Robert,

I’m not too familiar with that particular type of sensor, but based on the information I’ve been reading I believe the signal conditioner automatically centers the voltage at zero, and the positive or negative magnitude of the voltage tells you the displacement in either direction.
https://www.ni.com/en/shop/data-acquisition/measuring-position-and-displacement-with-lvdts.html#sect...
You may be able to create a custom scale for your DAQmx task with the conversion from voltage to displacement:
https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z0000019KyDSAU&l=en-US
I don’t know what programming environment you’re using, but the DAQmx driver comes with some built-in examples for both LabVIEW and text-based languages that should help you get started doing analog input:
https://www.ni.com/en/support/documentation/supplemental/18/ni-daqmx-example-locations-for-labview-a...
https://www.ni.com/en/support/documentation/supplemental/21/using-ni-daqmx-in-text-based-programming...
https://www.ni.com/en/support/documentation/supplemental/06/getting-started-with-ni-daqmx--main-page...

Kelsey Johnson

Applications Engineer

National Instruments

[RobertUWM]

Thanks for the links Kelsey Johnson, those links will come in handy.

Unforunatly the signal condition does not auto center the voltage at zero, it just turns the signal into a DC output.

Knowing this, I would need to first read in a voltage to mark as my zero then compare all of the rest of the voltages to this one. Any suggestions on how to do this with DAQmx in a LabView enviroment? All I have been able to do so far is read in a constant stream of voltage readings.

[K_Joy · Accepted solution]

The best way to set this up would be a state machine. If you search the NI Developer Exchange for DAQmx state machines, there are a lot of good examples for how to set one up. There is also a built-in template for a state machine in LabVIEW with a lot of information for setting it up.

http://search.ni.com/nisearch/app/main/p/bot/no/ap/tech/lang/en/pg/1/sn/ssnav:cod/q/daqmx%20state%20...

What you would want to do is have an initial state where you are reading data. When you are sure the displacement is at 0, you could press a button to read a “zero” value, and then use that recorded value (in a shift register) as an offset for all of the data you read after that point.

The state machine may be more complicated than what you need, but it is probably the most robust solution. If you are acquiring data in a loop, you could simplify it by just having a case structure in the loop to record the offset when the button is pressed. I’ve attached an example of what the basic structure of that might look like.

If you’re not concerned about the reading not being “centered” the first time you read data, you could just use the First Call? function to initialize the offset with the first value you read. 

Kelsey Johnson

Applications Engineer