why the voltage is 5 volts when the loop is open

[connector]

I am trying to use SCXI 1102 to aquire analog signal(0~5 volts). Why I got 0 volts signal if the loop is closed(for example: If channel 10+ and channel 10- is connected together) while 5 volts signal if the loop is open(channel 10+ and channel 10- is not connected to each other)?

I am using SCXI 1000 chassis and SCXI 1102 connect to DAQ board(PCI-MIO-16XE-50). I can configure virtual channels for SCXI 1102. How can I configure virtual channels for the rest of my modules(I still have SCXI 1160, 1124, 1180)?

Thanks

connector

[gbush]

Amplifiers wothout any input load will "float" to a power supply limit, sometimes plus, sometimes -.You cam, not scan that channel, scan the channel and ignore, wire the channel to your field loop, or install a resistor across the terminals. I usually use a 10K resistor.

[Filipe A.]

Hello;

Instrumentation amplifiers amplify the voltage difference in between inputs - and +. In case you short the inputs together, the difference voltage will be zero, meaning you will get a 0V result.

In case you don't connect a valid signal source to the instrumentation amplifier inputs, its inputs will float, meaning the amplifier will saturate to its maximum reference voltage.

Hope this helps.
Filipe A.
Applications Engineer
National Instruments