Lightning Protection Surge Protector for Measurement and Control Systems

 Phoenix Measurement and Control System Surge Protection Lightning Arresters

Compared to power systems, measurement and control systems are more sensitive to surges. As the central nervous system of a factory, they have extremely stringent safety requirements. Therefore, surge protectors with protective circuits are used for system protection. They are installed directly before the signal inputs that need protection, effectively preventing coupled surges and safeguarding interfaces.

Two-wire analog measurement is commonly used for flow and level measurement. Voltage signal measurement includes querying potentiometer positions or slider settings. In Ex(i) zones, temperature and level measurements are required for tanks. The connection system and required space must comply with the installation environment. This is why MCR surge protectors are suitable for various connection systems.

The selection of surge protectors is based on the following four factors:

• Signal processing, such as 2, 3, or 4-wire systems
• Maximum voltage signal
• Surge withstand capability, and
• Transmission frequency.

The operating environment of the surge protector must also be considered. For example, protection for intrinsically safe circuits has special requirements for surge protection. The PLUGTRAB PT pluggable protector or modular COMTRAB product series are extremely convenient to use. During service or maintenance, reinstallation is not required. Simply remove the plug from the base and test it using the CHECKMASTER tester.

Common Signal Types Requiring Protection 

Two-Wire Switching Signal Measurement with Common Reference Level
In the case of binary switching signals (e.g., signals shared by positioners), the voltage is transmitted to other signal lines at a distance based on the switch position. This voltage typically depends on the controller's reference potential and can operate either floating or non-floating. Transient surge voltages between the signal line and reference potential must be limited to acceptable levels.

The schematic diagram of this type of protection circuit is as follows: m



Two-Wire Analog Measurement
Here, we refer to signal circuits without a common reference potential with other signal circuits. The most common example is the 0(4)-20 mA current loop. The physical value to be measured is converted into a current value. It is anticipated that coupling from transient surge voltages is primarily symmetrical, i.e., occurring between the relevant signal lines. Therefore, voltage-limiting components must be installed between the signal lines.

The schematic diagram of this type of protection circuit is as follows:



Three-Wire Analog Measurement
Three-wire measurement can be used, for example, with PT100 thermistors for temperature measurement. Current flows through the thermistor via two signal lines, and the third line is used to measure the voltage drop.
Transient surge voltages between any cores can endanger the input side of the measurement sensor. This means that protective components must be installed between all cores to limit this voltage to a minimum.

The schematic diagram of this type of protection circuit is as follows:



Four-Wire Analog Measurement
In the case of four-wire measurement, current flows through the sensor via two lines, and the other two lines measure the voltage drop, for example, in a PT100 thermistor measurement loop. Directly measuring the high-impedance voltage at the sensor means that power consumption on the feed lines does not affect the measurement result.
Transient surge voltages between any cores can endanger the input side of the measurement sensor. This means that protective components must be installed between all cores to limit this voltage to a minimum.

The schematic diagram of this type of protection circuit is as follows:



Intrinsically Safe Circuits
Surge voltage protection devices used in intrinsically safe circuits must meet special requirements. International standards must be adhered to, such as EN 50 020 / DIN EN 50 020 / VDE 0170 / 0171 Part 7:1996-04; DIN VDE 0165 and TRbF 100. The insulation between intrinsically safe circuits and grounded components or enclosures must withstand an AC test voltage of 500Vrms.

The schematic diagram of this type of protection circuit is as follows:



In process/plant automation signal products, based on protection line pairs, usage locations, etc., they are divided into three types of products:

• Primarily for flow, pressure, level, and temperature signals where instrument installation points are relatively dispersed and require frequent updates and maintenance: The product is described as MCR－PLUGTRAB
  =Measurement/Control and Regulation－Pluggable + TRAB/surge absorption, simplified to model PT－XXX－XXX

• Primarily for the control room side of measurement and control systems, where there are relatively many lines and relatively limited space: The product is described as: TERMITRAB
  =Terminal-style + TRAB/surge absorption, simplified to model TT－XXX－XXX

• Primarily for the control room side of measurement and control systems, where there are relatively many lines, relatively limited space, and high maintenance requirements requiring pluggability: The product is described as COMTRAB = COM/(multi-)channel + TRAB/surge absorption, further divided into:
  
• CT10… = 10-channel integrated protector.
  
• CT8… = 8-channel integrated protector.
  
• CTM－XX = COM + TRAB + Modul: Combinable channel protector.

Selection Guide

Signal Description	Application	Pluggable	Model	Number of Protected Wires
Current loop 0(4)-20mA	Process measurement Level/flow measurement (suitable for long-distance transmission)	Yes	PT 2X2-24DC-ST and BE	2 pairs
			PT 1X2-24DC-ST and BE	1 pair
			CT-2PE… with CT-TERMIBLOCK terminal block	8 or 10 pairs
			TT-2-PE-…	1 pair
		Yes	CT…2PE… with standard patch panel (wire stripping not required)	8 or 10 pairs
	Level measurement	Yes	PT 2X2…	2 pairs
Voltage signal 0-10V	(suitable for short-distance transmission)		CT…2PE… with CT-TERMIBLOCK terminal block	8 or 10 pairs
			TT-2-PE-…	1 pair
		Yes	CT…2PE… with standard patch panel (wire stripping not required)	8 or 10 pairs
	Travel signals, etc. (on/off signals)	Yes	PT 4X1… with PT 4X1-BE (base)	4 wires + GND
			CT…2/2… with CT-TERMIBLOCK terminal block	16 or 20 wires
			TT-2/2-…	2 wires
		Yes	CT…2/2… with standard patch panel (wire stripping not required)	16 or 20 wires
			PT 4X1… with PT 4X1+F-BE	4 wires + GND
			CT10-18…+F/PE… with CT-TERMIBLOCK (terminal block)	18 wires + GND
			TT-2/2-…+UBK 2…	2 wires
		Yes	CT10-18…+F/PE… with standard patch panel (wire stripping not required)	18 wires + GND
24V measurement and control signal	PT100 temperature measurement technology	Yes	PT 4… with PT 4-BE	4 wires
Intrinsically safe circuits with Ex-marked explosion-proof products	Level/level measurement in tanks	Yes	PT2xEX(I) -24DC-ST and BE	2 pairs
			TT-EX(I)	1 pair
	PT100 temperature measurement technology	Yes	PT 4-EX(I)-24DC-ST and BE	4 wires