SCC-SG01 output can not exceed +1.9V?

[gangmei]

I am using SCC-SG01 inside SC-2345 with PCI-6034E card to measure resistance. The output voltage should be -10V to +10V(idealy 0V when connnected to a 120Ohm resistor).
In my experiment, by increasing the value of resistance or adjusting  the potentiometer, I can eventually get -10V output reading on my PC(with labview). However, no matter how I decrease the value resistance or adjust the potentiometer, the output can never execeed +1.9V, the maxium I got is about 1.87V.

Any explanation and fix for this?

Thanks a lot.

[Otis]

Hi gangmei,

You may want to check out this tutorial to make sure that you are connecting everything correctly.
SCC Tutorial Series: SCC-SG0x 

I was a little confused with what you stated when you said you could adjust the potentiometer to -10V in one place, but in the next sentence you said it would only adjust to 1.9V.  Typically you should not have a difference of more than +/- 5 V if you are connected to the half-bridge circuitry due to the nature of a Wheatstone circuit and the 10 Vex that the SCC-SG0X provides.

Regards,

[gangmei]

My connection is like Figure 4 in that tutorial. The purpose is to measure the resistance of RG. Therotically, if I leave RG open (RG = infinite), the ouput should be -1.25V * 100 which will be limited to -10V. I can increase RG to reach this point.

But in another direction, if I short RG(RG = 0), in theory the output should be limited to +10V. But I could not manage to reach.

Sorry I am not sure I understand what you said about the difference should be +/-5V.

Thanks a lot.

[Otis]

Hi gangmei,

Sorry about some of the confusion from the last post.  The thing about +/- 5 V was a mistake on my part, so you can forget about that.  I thought you were using an SCC-SG24 and were using a potentiometer to get your actual measurements.

You said that you can get your measurements to swing in one direction, but not the other.  The range for the SCC-SG01 is only +/- 100mV, so I think you should be able to see the full voltage swing without problems.  Do you have any other SCC-SG01 modules that you could test to see if they are getting the same behavior?

Additionally you mentioned that you were using a potentiometer to play with the values of your resistance.  Is there any chance that this potentiometer has a minimum resistance and that could be why it won't swing fully in the other direction?  What happens if you actually short the resistor you are measuring?

Thanks,