differential channel

[confused01]

Hi,

I have been using SCC-SG01 modules to measure strain and I adopted the "Aquire and Graph" template in Labview to record the direct output voltages from the modules. I have placed an active strain gauge in channel x+ of the SG01 module, and a second active gauge in the x+8 channel of the module. I have correctly wired the gauges across the terminals of the module (this has been triple checked). On the output data, if I vary the strain in the gauge connected to channel x+ ONLY (with the other gauge under no strain) I see the voltage output varying for this channel only, whilst the second voltage output remains constant. If I then leave the gauge connected to x+ unstrained and strain the gauge connected to x+8 only, the voltage outputs for BOTH channels vary in an equal and opposite manner.

Have I missed something in terms of the differential channels?

Any help is much appreciated. I am going round in circles reading the manuals.

[Stuart.Parkinson]

Can you post a diagram of exactly how you have wired these.

[pallen]

You do need to check your wiring again...but, I have seen something similar to this in the past when using single ended, high impedance sensors; ghosting of readings on other channels. 

Again, this may not be the issue you are facing.  But the problem was essentially that the filter capacitor on the DAQ wasn't able to drain quickly enough when scanning multiple channels. 

NI has an article here on how to change the interchannel delay. 

Another technique is to have an empty or grounded channel between the two channels in the scan order. 

Good luck.

[confused01]

Hi Stuart, thank you for your response. I have drawn a rough diagram of how I wired the two active gauges to the SG01 module. I then placed the module in channel 0/8 of an SC-2345.

[confused01]

Hi Partrick,

If ghosting were the issue, would I see ghosting in both channels x and x+8? Regardless of where I place the module (ch 0/8, 1/9, 2/10 etc), the only gauge that affects both outputs is the gauge wired to the second channel (8, 9, 10 etc).

I am yet to try both your suggestions given the Easter break, but as soon as I can I will give them a go.

Thank you for your help!