Effective Lightning Protection Methods for Intelligent Instruments

1. Overview

Most of the industrial computers, various communication modules, security devices and field measuring instruments in the intelligent instrument control system use integrated circuit combinations of electronic devices. These micro-electric devices generally have fatal weaknesses such as low insulation strength and low surge resistance. They are often damaged by lightning strikes during thunderstorm seasons, which may cause partial damage to the input and output modules of several instruments and computers, or even cause the entire device control system to be paralyzed and forced to stop work for maintenance, causing huge losses. Therefore, it is very necessary to add lightning protection devices to these control and production devices.

2. Lightning Intrusion Path

Lightning surges can cause computer and communication failures. When the surge exceeds the computer's tolerance, garbled data will appear, chips will be damaged, and even software systems will be damaged, causing interruptions in receiving/transmitting data.

The study of lightning protection for intelligent instrument control systems should start from two aspects: external system lightning protection and internal system lightning protection. External lightning protection measures mainly address the hazards of induced lightning strikes to measuring instruments. The main surge intrusion pathways include the introduction of induced surges from signal cables into the measuring instrument circuits, which damage the insulation, break down micro-electric components, and cause instrument failures, and direct induced lightning strikes through the meter body and directly into the instrument circuit, breaking down the circuit module and causing failures. The solution is to review the overall lightning protection measures of the device and the grounding of signal communication cables, reasonable wiring, and grounding of metal instrument boxes according to the requirements of lightning protection specifications. Surge devices should be installed for the protection system of key interlocking signals; the internal lightning protection system mainly refers to the power supply lightning protection of the intelligent instrument control system, the grounding of data processing equipment such as the control display unit, operating system, and engineer station, as well as the lightning protection of the signal channels in and out of the computer and the lightning protection measures for signals and power supplies such as switches and network cards associated with the local area network.

3. How to prevent lightning strikes

3.1 Improve the grounding system

(l) The grounding of the safety protection ground, control cabinet, operating table, engineer station, power cabinet and other casings must be connected together with flat steel.

(2) The instrument signal ground and computer input and output signal ground are the reference points for instrument measurement. All instrument working power supplies, such as the negative terminal of 24V, are connected to this ground to form the same potential.

(3) The grounding of intrinsically safe ground, safety barrier, isolation barrier, safety device, etc. must also be connected to the instrument signal reference point to form an equipotential system. The grounding is concentrated at one point and the resistance cannot be greater than 1Ω.

3.2 Surge protection of idle source

The power supply of the intelligent instrument control system enters the computer control room from the power distribution system. The power supply system is from the power plant through the transformer and the power distribution system to the instrument system. In thunderstorm weather, the power supply is transmitted in due to the long loop and is likely to be struck by lightning. Therefore, the power supply at this time is not 380v or 220v, 50Hz AC, but a surge voltage mixed with various noises. If the surge protection system is not set up, the electrical equipment in use will exceed the withstand voltage limit and cause an accident. Connect the A, B, C, and D three-wire four-phase of the total power distribution to the A, B, C, and D terminals corresponding to the power surge protector. During a thunderstorm, the induced lightning surge is protected by the surge protector to sink the overload current into the earth, and the output voltage is clamped in the safe working area to ensure the safe operation of the power supply.

3.3 Signal channel surge protector

The signal channel surge protector should ensure that the instrument's various detection information is transmitted accurately, stably and flexibly under normal conditions, and can discharge overvoltage surges to the ground during thunderstorms, clamping the output voltage in a safe area, thereby ensuring the safety of signal transmission. From the use effect, the installation of surge protectors for lightning protection has greatly improved the safety factor of intelligent instrument devices during thunderstorms.

The following factors should be noted when applying lightning protection products:

(l) Regularly check and maintain the power supply system of the intelligent instrument control system project, the rust and breakage of the busbar and grounding body, and repair them in time to restore them to normal. Regularly check the resistance (the resistance should be kept at 1). If the resistance value increases, find out the reason and reduce the resistance.

(2) Perform annual inspections on surge protectors in proportion to the voltage of the electronic components. This is because after long-term use, the operating voltage of the surge protectors will drop due to aging, causing the lightning protection parameters to fail to meet the standards.

(3) Power lightning protection grids are generally used in power distribution systems. Many products have alarm devices. Once the lightning protection grid is overheated, the device will automatically disconnect and send out photoelectric and acoustic alarm signals. Its appearance and leakage grounding corrosion should be checked regularly. When selecting a power surge protector, pay attention to the size of the load and choose a suitable surge protector.

IV. Conclusion

In order to ensure the safe and reliable operation of intelligent instrument control systems in industrial production, it is imperative to learn and draw on advanced lightning protection measures and select high-quality lightning protection products.