Measuring Unexpected Temperature with NI-9213 in NI MAX

Issue Details

• I am unable to measure the expected temperature with a NI 9213 module using a thermocouple in NI MAX Test Panels. The values read back are extremely higher (~1.38k) than the expected temperature range and the behavior is uniform across channels. How can I acquire the right temperature measurements?

Solution

• The measured value 1.38 k indicates that your DAQ device has detected an open thermocouple on the channel. This could be due to a fault in the thermocouple, breaking of thermocouple junction or improper connection of thermocouple terminals with DAQ device channel connectors. This causes the Open Thermocouple Detection circuitry inside the device to pull up the measured voltage to full scale reading.
• Some DAQ devices such as NI 9214 have the option to disable OTD circuitry which will give result as 0 during open circuit.

Troubleshooting steps - 

1. Open the NI MAX Test Panel for NI-9213 & verify that the Thermocouple Type selected matches with your thermocouple specification.
2. Connect the thermocouple wires appropriately with your 9213 channel. Do not use clamper cables, crocodile cables, soldered wires to connect to the channel. This will lead to inaccurate results. Connect either the thermocouple terminals directly or use the wires along with the thermocouple package.
3. Check your thermocouple for faults or breaks. One good way of checking whether your thermocouple is functioning properly is by using thermocouple chart & measuring thermoelectric voltage in a known temperature environment using a Digital Multimeter.
4. Check the physical connection of your thermocouple terminals with the DAQ channel terminals.

Additional Information

The Open Thermocouple Detection feature is essential to identify the breakage in the Thermocouple Junction. Many applications have zero temperature as a valid measurement value & if OTD feature is disabled, it would be very difficult to figure out whether the measured zero value is the actual temperature reading or it is due to an Open Channel.