On-site surge protector

It’s likely you’ve made a mistake; the surge protector on the field side is of the type shown in the diagram below, connected in series at the instrument interface. The rail-mounted type you mentioned is located on the cabinet side.

Under what circumstances is it necessary to install surge protection? We’ve never had it installed here

Copied from the Internet: A Brief Discussion on the Design of Lightning Protection Systems for Instrumentation and Automation Systems, Ningxia Industrial Institute, 2009/3/12 13:49:00. 1. Surge protectors are not safety barriers for intrinsically safe systems; their structures, types of components, and operating principles are all different, as are their functions and efficiencies. Therefore, they cannot be used as substitutes for one another. 2. Principles for installing surge protectors 2.1 Considerations should include the average annual number of thunderstorm days in the area where the factory and equipment are located, the estimated annual number of lightning strikes on the equipment, lightning risk assessments, and the required lightning protection level. 2.2 The installation of surge protectors should take comprehensive economic losses into consideration, and they should not be installed indiscriminately. For example, if the total economic loss caused by damage to on-site measuring instruments exceeds 100,000 yuan, surge protectors should be installed at those instruments ； If the total economic loss resulting from damage to the instruments in the control room or those used for signal processing exceeds 100,000 yuan, surge protectors can be installed at both the field measurement instruments and the instruments in the control room ； 2.3 Surge protectors should be installed on the signal circuits of the field measurement instruments, and surge protectors should also be provided for the instruments in the control room ； 3. Surge protector installation scheme 3.1 When the horizontal distance between the signal cable and the ground is greater than 100 m, or the vertical distance is greater than 10 m, surge protectors should be installed at both the field measurement instruments and the instruments in the control room. 3.2 Instruments with surge protectors: Surge protectors should be installed at both ends of the safety instrument system. Surge protectors should also be installed at both ends of the transmitters in the field as well as those in the control room. Surge protectors are required at both ends of field signal actuators such as electrical converters, electrical valve positioners, solenoid valves, and other similar instruments, as well as those in the control room. Surge protectors should be installed at both ends of the thermal resistors and thermocouples, as well as on the instruments in the field and control room. Surge protectors should also be installed at both ends of the electronic switches in the field and control room. Where UPS units are used, surge protectors for the AC power supply lines should be installed on the input side of those UPS units. Among the instruments that require surge protection as mentioned above, surge protection is not necessary at the field terminals of thermocouples and thermal resistors ； A surge protector may not be required at the field end of the contact switch ； Surge protectors may not be required for the pump signals coming from the power distribution room and electrical control room. 4. Types of surge protectors: Surge protectors are classified according to their application areas, including signal instruments, network communication devices, DC power sources, AC power sources, etc. The installation of surge protectors should be determined based on the electrical characteristics of the circuit to be protected. For 4–20mA signal instruments with a nominal supply voltage of 24VDC, in two-wire, three-wire, or four-wire configurations, where the DC power supply for the circuit serves as the signal power source, surge protectors should be installed according to the requirements for such signal instruments. DC power supply units belong to the category of DC power supplies, and surge protectors should be installed for them. The AC power supply for four-wire metering instruments powered by alternating current should be of the AC source type, and surge protectors should be installed in accordance with the requirements for such AC sources. The parameters of the surge protector must be suitable for the signal level and immunity of the instruments to be protected, as well as for the characteristics of lightning surge currents in that particular environment; the selection cannot be made arbitrarily. Maximum continuous operating voltage Uc: For instruments powered by 24V DC, the maximum signal voltage ranges from 30 to 36VDC; therefore, the maximum continuous operating voltage is 36VDC or higher. Maximum signal current Ic: For 4–20mA signal instruments with two-wire, three-wire, or four-wire configurations (including those using the HART and PROFIBUS protocols), the maximum signal current is 150mA or more ； For 24V DC supply circuits, such as solenoid valves, ultrasonic instruments, combustible gas detectors and other devices, the maximum signal current value is: greater than or equal to 600mA. The nominal discharge current In: For signal instruments, a value of over 1kV is sufficient to meet general protection requirements; 5kV and 10kV are the standard values chosen. (Important parameters) Voltage protection level Up: For instruments designed to operate at 24VDC, the voltage protection level of the surge protector is 60V. Response time: The response time for signal-related surge protectors is less than or equal to 5 ns. Operating frequency: For instrument signals, including \"smart\" instruments, the operating frequency ranges from 1 to 20 kHz; this value is usually not necessary to specify.

Current design requirements mandate the inclusion of surge protection, and it is needed both in the cabinets and at the site. Your approach is incorrect; if surge protection is added to the on-site wiring box, isn’t that the same as adding it inside the cabinet? It should be installed on the field instrument.

Yours is an external transmitter; I currently choose built-in transmitters for mine, so there’s no need to add one

Boss, take a look at the pictures I’ve posted below. It says in the sample that there are two types: one with guide rails placed in the on-site side junction box, and another type for the cabinet side – they seem to be different

The models on the field side and the cabinet side seem to be different @gaiyin47

Bro, I checked and this one is in parallel configuration, right? @zhuirvine The rail-type one seems to be in series configuration

Placing it in the on-site junction box is the same as placing it on the DCS wiring rack; both are located on the circuit, which amounts to duplicate setup. Look at the method on the second floor; there is a surge that needs to be connected to the instrument.

Surge protectors are a type of lightning protection measure; for more details, refer to Chapter 4, Section 1 of Part 5 in the fourth edition of the \"Petroleum and Chemical Industry Automatic Control Design Manual\", which provides an overview of lightning protection design for instrumentation and control systems.