Temperature: What is the best way to measure temperature from thermocouples for a control loop?
A digital multimeter, such as the Keithley Model 2000 or 2700, can be used to measure the voltage and convert the value to temperature for the type of thermocouple being used. The multimeter will send the digital data to a computer as a temperature value. The computer can be used as the control. Data can be sent at rates up to several hundred readings per second with digital multimeters.
Data acquisition cards with temperature capability and cold-junction compensation, such as models KPCI-3108, KPCI-3107 or KPCI-1801HC, can be used at higher rates. In this case, the millivolt signal measured by the plug-in board would need to be converted to a temperature by the controlling software. The Thermocouple COM object is a free download from this site; it greatly simplifies the math required for the volts to temperature conversion.
Another solution would be the M1300 Series RS-232/RS-485 Measurement Modules. The M1300 Series can accept J, K or T thermocouple inputs and have digital outputs that can change state at programmable upper and lower alarm limits. Reading rates of 8/second can be achieved with these single channel modules.
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