Academic Company Events NI Developer Zone Support Solutions Products & Services Contact NI MyNI
2 ratings:
 3 out of 5     Rate this Document

Using VI Logger With Thermocouples And Built In Cold Junction Compensation (CJC)

Primary Software: Driver Software>>NI-DAQ
Primary Software Version: 7.0
Primary Software Fixed Version: N/A
Secondary Software: N/A

Problem: I am using VI Logger to log my thermocouple measurements. I create a Virtual Channel in Measurement and Automation Explorer and when I test it I get the correct measurement. When I run VI Logger the numbers do not show up on the graph and I get IND.# as the value.

Solution: This is expected behavior with VI Logger, it is because the CJC was selected as 'built in'. This error will occur when using SCB or SCXI Terminal blocks (such as the SCXI-1300) that have a built in Cold Junction Compensation. There are a few different ways to get the correct data:

1. For the SCB Series create a voltage Virtual Channel for channel zero (the SCB should still be configured for temperature measurements) and check the 'this will be a temperature measurement' box. Then select 'User Supplied' as the CJC source in all Thermocouple channels. With the SCXI Terminal Blocks a channel will have to be created using an IC sensor or Thermistor, this can be any channel.

2. Select the CJC Source to be 'User Defined' and choose a temperature that is close to the operating temperature in the room the thermocouples are in. Some accuracy in the measurements may be lost if the temperature supplied is not close to the temperature in the room.

3. To keep the 'Built In' source for the CJC go into VI Logger and select the current NI-DAQ Task. Select the Calculated Channels Tab and create a new Calculated Channel. The formula to be applied will be "Ax (Op) By + C" and select A = 1, B = 0, C = 0 and x = Thermocouple Channel. The channel for y can be left blank.

Now when testing the channels created in VI Logger data will be displayed and logged properly.

Related Links:

Attachments:





Report Date: 07/21/2003
Last Updated: 02/17/2006
Document ID: 2ZK7JPYB

Your Feedback! poor Poor  |  Excellent excellent   Yes No
 Document Quality? 
 Answered Your Question? 
  1 2 3 4 5
Please Contact NI for all product and support inquiries.submit