VirtualBench

[Curt D]

I am trying to switch from using thermocouples to thermistors. I am using a TBX-68T terminal block and an NI 4350 voltage meter connected to a computer running VirtualBench 2.6 via USB. When I plug a resistor of known value into the TBX-68T and excite it with current from the IEX0- and IEX0+ ports, VirtualBench will display the correct value for resistance. Then when I replace the resistor with a thermistor, VirtualBench will show that the resistance values vary inversely with temperature as expected. At this point, I change the VirtualBench settings to thermistor and input the correct A B and C values. When hit start, VirtualBench displays a static value of -273.15 degrees C. What is the problem?

Message Edited by Curt D on 05-16-2005 10:45 AM

[gaving]

Hey Curt,
There are so many places where one thing might be wrong. Let's just start with the thermistor. Can you read a VALID resistance back with a handheld DMM? (not plugged into anything) When you connect it and start the acquisition, can you read back a valid voltage (across the thermistor) from the handheld DMM? Do you have the TBX-68T set up as an accessory for the 4350 in MAX? (Devices and Interfaces>>Traditional NI-DAQ Devices>>right-click on the 4350 and choose "Properties"). Try either way. Is your cable loose between the TBX-68T and the 4350? Are your limits set up correctly (the utility where you configured the A,B and C components)? What happens when you leave the A,B and C constants the default values?

Please let me know.

Sincerely,
Gavin Goodrich
Applications Engineer
National Instruments