Application of digital multimeter in field instrument maintenance

Digital DC mv block, its resolution is 0.lmv. It is very convenient to use a digital multimeter to identify the type of thermocouple and distinguish the positive and negative poles. Place the hot end of an unknown type of thermocouple in boiling water or a container with a certain temperature, use a digital multimeter to measure the thermoelectric potential value, and then add the cold end potential values ​​to determine the graduation number of the thermocouple. It is also easy to determine the positive and negative poles of the thermocouple. If the temperature does not match the instrument indication, a digital multimeter can be used to measure the thermoelectric potential of the thermocouple to compare and determine the cause of the fault. In situations where the requirements are not high, a digital multimeter can be used instead of a DC potentiometer for measurement. Compared with a DC potentiometer, a digital multimeter makes testing much more convenient due to its compact size.

The electrical resistance of a digital multimeter has a resolution of 0.1ω. In situations where the requirements are not high, a digital multimeter can be used instead of a DC bridge to measure the resistance of the thermal resistor. When the on-site temperature does not match the instrument indication, a digital multimeter can be used to measure the resistance value of the thermal resistor. The difference between the resistance value of the thermal resistor and the actual temperature can basically determine whether it is normal. Measuring the resistance value of the connecting wire can determine the wiring and contact. Is it normal? It is also very convenient to use a digital multimeter to check and measure small resistance resistors during instrument repair.

The DC ma block of the digital multimeter has a resolution of 0.0lma; the DC voltage block has a resolution of 0.01v. It is very convenient to use these two blocks to measure the 4-20ma output current of the transmitter and the converted 1-5v voltage. of. Although its reading cannot be used as a standard, it can be used to judge the indication status of the transmitter and display instrument on site.

It is common for field instruments and terminals to have poor contact. You can directly use the circuit on-off switch of a digital multimeter to test. In this way, you don’t need to read the meter’s instructions. You can judge whether the terminal connection is normal by listening to whether the buzzer in the meter sounds. , if it is tested on-site at high altitude, its superiority is even more reflected.

When there is suspicion of interference in instruments and control systems on site, you can use the AC voltage range of a digital multimeter to measure the interference to determine the size of the interference.