Using Thermocouple Panelettes with Non- J or K Type ThermocouplesHardware: SCC>>Carriers>>SC-2345
Problem: I would like to use panelettes with my SC-2345, SC-2350, or CA-1000 to connect to my thermcouple, but it is not a J or K type thermocouple. Is there an option for other thermocouple types? Solution: National Instruments provides three kinds of thermocouple panelettes, the J, K, and the Uncompensated Type for the SC-2345, SC-2350, or CA-1000. The specific jack for the J or K-type thermocouples connects to a terminal on the internal side of the panelette through the same metal and wire as the thermocouple, so it is an extension of the same type of metals that make up the thermocouple. This extends the point of cold junction voltage back to the measurement device connection where the cold-junction compensation sensor is located. If the wrong thermocouple type is used with the J or K-type specific connector, a significant error would arise because the Seebeck Effect introduces additional voltage in the junction between the thermocouple and the jack. If you are not using a J or K type thermocouple, you can purchase uncompensated thermocouple panelettes for your system. Uncompensated thermocouple panelettes are referred to as type U and have the same type of metal (copper) on both connector inputs, and this metal is used for the wires that extend back through the chassis to the module. This is an acceptable method of connection for thermocouples, but there can be error introduced because of differences in the temperature at the jack (which is on the outside of the SC-2345 carrier) and the temperature at the CJC sensor (which is inside the enclosure). For most indoor applications, the carrier is in a controlled temperature environment and the temperature difference between the jack and the module's CJC sensor is minimal, thus the associated error will be small. Each panelette has two individual thermocouple jacks on it. You have two choices for type U panelettes:
If you would like to extend the cold junction to the point of measurement with an uncompensated thermocouple jack, you can purchase thermocouple wire that matches the type of thermocouple you are measuring. Use this wire instead of the copper wire that comes with it to connect each thermocouple jack to the input of your measurement device (for example, the SCC-TC02). Related Links: Developer Zone Tutorial: Fundamentals of Thermocouples KnowledgeBase 3ULBHSZA: SC-2345, SC-2350, and CA-1000 Chassis Size and Panelette Capacity Attachments:
Report Date: 05/17/2002 Last Updated: 09/26/2007 Document ID: 2LGA3FUL |
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