Force sensor readout

[Thibault_Prevost]

Hi,

I have an LVDT and a force sensor (both attached to a motor) plugged into an SC-2350 board. The force sensor is connected to the board via an SCC-SG04 module. The force signal is very noisy and needs some filtering. I currently use a simple 1Hz lowpass filter.  Below is what I get whenever the module SG04 is connected to the board (figure 1) or disconnected from the board (figure 2):



Figure 1: force sensor module connected to board



Figure 2: force sensor disconnected from board.


The top graph in each picture is the sine voltage output to the motor.
The terminal configuration for the force sensor module is set either to "<Let NI-DAQ Choose>" or to "NRSE" (the other measurement options are grayed out).
Why do I get a clearer periodic signal from the physical channel of the force sensor whenever the SCC-SG04 module is disconnected from the board?! I would have expected nothing but close to 0 noise instead... In the nonreferenced single-ended measurement system, what would the reference ground be in my case?

Thanks for your help,

Thibault.

[CDancer]

An open analog input has a very high input impedance so tends to pick up all kinds of signals from nearby voltage sources. My guess is it is picking up some of the LVDT signal.

In NRSE, the reference is the AISense pin. If you connect this to analog ground you have the same setup as RSE. I have always thought those names really confusing - in non-referenced mode, there is a reference input, but in referenced, there is no reference input!

Chris

[Thibault_Prevost]

Thanks. 2 questions: what would the AISense be for the SCC-SG04 module? I only have two pairs of analog inputs and V+/V- voltage outputs. Physically, how would the open analog input "pick up" the LVDT signal? Is there any way I could work around this?

Thibault.

[samantham]

Hello,

I have linked at helpful Knowledge Base below.  It explains why you are getting a reading on the open channel.  Please try to ground the channel you are interested in

reading 0 Volts on or remove the channel from the graph.  On the SCC-SG2350, you can wire the channel inputs to ground.  I have also attached the manual from the

SC-2350.  Please look at Tables B-4, B-5, and B-6 for pin outs.

Incorrect Readings when Scanning Unconnected or Open Channels

SC-2345/2350 Carrier User Manual and Specifications