Regarding the grounding issue of armored platinum resistance thermometers
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An armored platinum resistance thermometer, if it does not come with a temperature transmitter, transmits the resistance value to the terminal cabinet, where a temperature transmitter located in that cabinet converts it into a signal suitable for transmission to the upper-level system. Is it necessary to provide lightning protection and grounding for such platinum resistance thermometer enclosures? All I know for now is about integrated platinum resistance thermometers, which convert the resistance value directly into a current value on-site before transmitting it to the host computer; such devices must be grounded. I’m new to instrumentation; please be gentle if my questions are too basic. Thank you to all the experts.
The enclosure does not require separate grounding; the shielding layer of the three-core cable can be grounded to the main control system.
Most instrumentation devices do not have explicit requirements for equipotential bonding and repeated grounding, unless otherwise specified. Things like thermometers, as far as I’ve seen, none of them have a dedicated ground connection. Furthermore, it is already naturally grounded to the installation through bolt connections. In some thermometers, the measuring element is connected to the housing, and attention must be paid to whether this has an impact on the measurement.
A temperature variation safety barrier for the thermoresistor inside the system cabinet is sufficient; the shielding layers of the cables should be connected together for grounding
For example, with these thermal resistors installed on the gas production tree, isn’t there any standard requirement that they must be grounded? If this platinum resistance thermometer is to be grounded, should it be grounded for shielding purposes, for lightning protection, or for protection?
Lightning protection grounding requires the use of surge protectors; simply grounding your instruments is not sufficient for lightning protection. Shield grounding is necessary. Thermal resistors do not require a protective ground. Additionally, there is an issue with the wiring of the explosion-proof disturbance-resistant tube in your picture; rainwater may enter the thermal resistor junction box in the future
Is the shield grounding of that thermal resistor connected together at the terminal cabinet? Is it not necessary to pour it on-site? Also, regarding the issue of wiring in explosion-proof wire glands you mentioned, it is necessary to place the wiring gland below the connection point of the thermal resistor, right? Thanks for the advice
The shield grounding of the thermal resistor should be connected uniformly at the cabinet side; it should not be connected on-site. The flexible tube should be positioned lower than the connection port.
The housing of platinum resistance thermometers must have protection/lightning protection grounding. But in most cases, there is no need to do it deliberately. The housing of the platinum resistance thermometer, just like that of the instrument, requires protection as well as lightning protection and grounding. However, as required, there is no need to take special measures for the protection/lightning protection grounding installed on metal devices or dials; as long as the enclosure is connected to the metal device or dial, it will together form a system for lightning protection or protection of the device or dial. Incidentally, the instrument insulation box and mounting frame should also have grounding devices or be connected to equipment with grounding. If the device or dial is a poor conductor, a grounding circuit must be provided. Wire ducts, explosion-proof flexible hoses, and instrument enclosures are treated in the same way. When wiring field instruments, thermal resistors, and thermocouples, the shield of the shielded cable used should not be electrically connected to the instrument’s enclosure.