Problems with the calibration of the temperature instrument circuit
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When the construction team carries out circuit testing, what equipment is used to simulate voltage and resistance signals for thermocouples and thermal resistors? When adding a signal, does one disconnect the wires of the thermocouple or thermal resistor and connect them to the device? How should we understand something like Fluke, which is connected to a thermocouple?
A field calibrator can solve this issue; there are many manufacturers available, which can be found on Baidu.
Fluke can be used to apply a signal to the circuit; it has functions for outputting mV and resistance signals. The method involves disconnecting the wiring of the thermocouples or thermal resistors on site, and then connecting Fluke’s signal directly to the circuit; several values can be supplied to check whether the display on the control panel is correct.
This post was last edited by xxkhc on 2017-8-31 at 22:23. A millivolt signal generator (which can be built oneself) can be used to simulate the signal of a thermocouple, while a resistance box can be used to simulate the signal of a thermal resistor; for calibration, a standard gauge is also required. High-priced on-site calibrators also consist of similar devices; their resistance output is a virtual resistance that requires a certain operating current. In contrast, resistance boxes provide genuine resistance values, making them more convenient to use. Also, the Fluke in your diagram is not connected to the thermocouple; rather, it outputs a millivolt signal to the temperature transmitter.
It’s simply to deceive the system by sending signals directly to the transmitter.
Resistance boxes are rarely used by construction companies, after all, it’s inconvenient to carry them around the site, and the temperature corresponding to each simulated resistance value needs to be looked up in advance
The connection shown in the diagram is not for loop calibration; rather, it is used to connect the signals from the field thermocouples to Fluke’s measurement terminal. This measurement terminal is typically used to measure the temperature at the compensation point, for cold-junction compensation purposes. Circuit debugging requires disconnecting the on-site temperature sensing elements
For loop debugging, it is necessary to disconnect the on-site temperature sensing element and use Fluke’s output to replace the sensing element in order to introduce the signal into the loop.
The image is a screenshot from Fluke’s user instructions, and it is labeled as a simulated thermocouple below the image
Thermistor circuit calibration: A resistance box is generally used, with a precision of 0.5 being sufficient. For thermocouples, the Fluke 754 can also be used; there is no need to connect it to terminals – it can be connected directly to your K-type compensation wire to transmit signals.