Measure negative voltage with SCXI-1121/1321 Combination

[rehbein]

I am trying to read a few millivolt level signal with an SCXI-1121 module using an SCXI-1321 terminal block. The module is connected to a PCI-MIO-16E-4 board through an SCXI-1100 chassis. The PCI-MIO-16E-4 board is configured to accept -10V to +10V signals in a differential mode. I am only able to read positive polarity signals. Whenever the input signal is of negative polarity, the measured value is locked at zero. Is this combination capable of measuring negative voltages or is there a jumper that must be set? Thanks.

[Patrick R.]

You shouldn't have a problem setting up your SCXI system to measure your millivolt inputs. Although, there are a few things you should keep in mind. First, determine the maximum range of your input signal. Afterwards, you can effectively select the range and gain that will provide the best results. There are a few jumpers within the module that are used to configure these settings. All jumper settings are described in the manual for the SCXI-1121, which can be found on our website. One other jumper to be aware of is jumper W33, which is used to set the mode of the device. You need to make sure it is in position A-R0R1 if your MIO card is configured for differential. Lastly, make sure that the gain settings for the device correspond with the gain settings in Me
asurement and Automation Explorer for each individual channel on the 1121 module. If these settings do not match, you could potentially experience bad results. I hope this information helps and resolves the problem. Have a good day.