The CPT is one of the versatile products offered by Moore Industries, serving as both a PC-Programmable temperature transmitter and a signal isolator/converter. If you need to monitor temperature using a Type J Thermocouple and provide two temperature-related outputs:
- An isolated 0 to 20mA (or 4-20mA) signal corresponding to the temperature range being measured, so that all 20mA covers the full span of degrees
- A separate isolated voltage output that precisely duplicated the actual thermocouple signal in millivolts
The proposed solution to the customer’s needs involved utilizing both the HLPRG Analog (current/voltage) and TPRG Sensor (RTD/thermocouple) input models of the CPT. The TPRG input model can be programmed for a Type J Thermocouple so that a specified 0 to 20mA output covers the desired temperatures if the entire temperature span of the thermocouple is not used. This provides excellent resolution over the desired temperature range.
The HLPRG input model provides the separate isolated voltage signal. Using the input signal from the CPT TPRG model and a 0 to 10Vdc output, the HLPRG can be programmed using published “Type J to Millivolt” charts and the CPT’s “Custom Curve” feature to convert current input values to volt output values. Since the CPT outputs only 0 to 10Vdc, no minus voltages are directly available. If the desired Type J Thermocouple is measuring temperatures below freezing, the programmer needs to add an offset to bring all the output voltages above zero volts. In addition, thermocouples are always in the microvolt to millivolt range, so adding an external voltage divider can drop the CPT voltage output into millivolt levels.
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