In order to protect sensors such as pressure, flow, temperature, and humidity in automatic control and instrumentation control from switching surges and lightning surges, surge protection devices (SPDs), surge prevention measures, and grounding methods suitable for sensor signal lines and power lines are required.

Key protective measures

1. Surge protection devices (SPDs) for signal and power lines

• Install surge protectors according to the type (4-20mA, RS-485, RTD, TC, etc.) for each sensor.

• Distributed installation: Parallel connection of surge protectors (Class 2, Class 3) to the instrument panel inlet, sensor terminals, each signal line, and power line.

2. Grounding measures against lightning and surges

• Connect the sensor and instrument panel to a low impedance ground (PE).

• Equipotential bonding of structures and metal cable trays minimizes potential rise due to lightning.

3. SPD specifications and installation standards

• Application of SPD products according to international standards such as IEC 61000-4-5, IEC 61643-21, and UL 1449.

• Select appropriate products (Varistor, GDT, TVS, etc.) according to the voltage and signal type of the equipment to be protected, and conduct repeated inspection and replacement.

4. Special built-in protector

• Built-in lightning/surge protection sensor products that are resistant to environmental changes such as moisture and temperature are available.

In general, automatic control sensor protection requires the installation of SPDs for signal/power lines, proper grounding and equipotential bonding, use of internationally standardized products, repeated maintenance, and application of special environment-specific sensors.

The most effective installation locations for SPDs (surge protection devices) for pressure, flow, temperature, and humidity sensors are at the points where signal and power lines enter/exit the field sensors (sensor terminals) and at the instrumentation control panel (master equipment entrance).

Effective SPD Installation Locations

• Sensor terminal (field unit)

Install SPD at the signal/power line inlet that is directly connected to the sensor.

First, block surges (lightning, switching surges) coming from outside.

• Control panel (master equipment) entrance

The point where the signal and power lines from the field enter the control panel

Add SPDs near I/O modules in the control panel to protect internal equipment and the entire system.

• Long distance wiring (over 10-15m)

If the signal cable is long between the sensor and the control panel, SPDs should be installed on both ends (sensor and control panel), especially recommended for external cables entering the building.

To maximize the actual protection effect, SPDs should be installed both at the sensor proximity (terminal) and at the control panel entrance, and designed as a continuous, multi-stage protection system (field + equipment entrance + intermediate cable) to prevent both external and internally induced surges.