NI Veristand: Connecting Linear Potentiometer To NI Veristand

[m15tertee]

Hello,

I want to connect a LP803-08 linear displacement potentiometer to NI Veristand.  There should be a way to get Veristand to map out the ports needed to hook up this sensor.  Does anyone have any information on this?  A manual of some sort would help out immensely.

Thanks!

Scott D.

[Craig_]

Hey Scott,

Based on the specs for that sensor on the page below it looks like the sensor's resistance varies as a function of distance:

http://www.omegaeng.cz/ppt/pptsc_eng.asp?ref=LP803&Nav=prej061

There are several ways to measure resistance. The best way is with a DMM and a Switch, as detailed here:

Resistance Measurements: http://www.ni.com/white-paper/3981/en/

However, DMMS and Switches are not directly integrated into VeriStand (you need custom devices to use them), so you may be better served measuring it indirectly:

Resistance Measurement - Indirect Method: http://www.ni.com/white-paper/14854/en/

The indirect method could be done with a standard DAQ card.

Does this answer your question?

Regards,

[m15tertee]

Hi Craig, thanks for the reply.  Resistance measurement techniques will be useful later once I get the sensors working.

To get the LP803 linear pots to work correctly, would I need to use a signal conditioner?  I have the analog DAC Pxle-4331 and TB-4330 connection devices.

Also, I don't see any custom bridge device on the Veristand.  Does the Veristand have this or do I need to order something extra?

Below are all the parts I have:

781368-01  NI PXIe-1071, 4-Slot 3U PXI Express Chassis
782340-33  NI PXIe-8135 Core i7-3610QE 2.3 GHz Real-Time Embedded SW
960903-02  NI Standard System Assurance Program for PXI
780590-35  NI VeriStand Full Development License
778965-01  NI PXI-6514 Industrial 32 DI, 32 Source DO Isolated DIO & NI-DAQ
781345-01  NI PXIe-4331 8-Ch Bridge Analog Input, 102.4kS/s
776990-01  SCB-100 Noise Rejecting, Shielded I/O Connector Block
781347-01  NI TB-4330 Terminal Block for PXIe-4330
185095-02  CABLE ASSY, Type SH100-100-FLEX, 2 m

Scott D.

[Craig_]

As of VeriStand 2012 you can use the PXIe-4331 natively in VeriStand. Previously you could use it in a custom device.

NI VeriStand Add-on: PXIe 433x: https://decibel.ni.com/content/docs/DOC-15404

Bridge measurements for this make a lot of sense. The PXIe-4331 should offer plenty of singnal conditioning, but I don't have much experience with the hardware itself, I'll look into this further next week.

How fast do you want your PCL to run? The 4331 has some rate requirements which often means you have to enable "Slow Background Conversion Rate": 

Analog Input Configuration Page: http://zone.ni.com/reference/en-XX/help/372846G-01/veristand/cp_ai/

Also you may want to add a X-Series DAQ card to the chassis to assist with engine timing. The PXIe-6341 is a good candidate for this.

There is some great discussion about synchronization in VeriStand here: 

Building Synchronized NI VeriStand Systems: http://www.ni.com/white-paper/14637/en/

[m15tertee]

I'm currently unsure on how fast I want the PCL to run; I'll get back to you on that.

The PXle-4331 does provide signal conditioning; according to the overview page, it says it "provides integrated data acquisition and signal conditioning for dynamic strain, load, and pressure measurements."  Can we tweak the module to provide signal conditioning for linear displacement measurements instead?

[Craig_]

The PXIe-4331 in this context providies signal conditioning for any generic wheatstone bridge measurement. While the documentation specifically calls out Strain, Load, and Pressure measurements these sensors act as resistors and are functionally no different than your linear displacement sensors. So yes, it will provide signal conditioning for this situation.

More discussion on this can be found here:

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

Please let me know if you have any other questions!