Compact Surge Protection Devices for 4-20mA Applications

4-20mA

The 4-20mA current loop is the dominant standard in the process control industry. It transmits process information via varying amounts of current, making it an ideal method for transferring process information as the current does not change as it travels from transmitter to receiver. The most substantial benefit of the 4-20mA protocol is that it is a widely accepted standard in industrial applications, meaning that many sensors and devices support the protocol natively.

4-20mA Applications

The 4-20mA analog current loops are widely used in various industrial applications. Here are some of the main applications: • Process Control: The 4-20mA current loop is the industry standard for process control applications. It is extensively used to carry signals from process instrumentation to controllers. • Proportional-Integral-Derivative (PID) Controllers: These are often used in control systems to adjust the process (such as temperature, pressure, etc.) based on the error value. The 4-20mA current loop is used to transmit the error value from the sensor to the PID controller1. • Supervisory Control and Data Acquisition (SCADA) Systems: SCADA systems are used for controlling and monitoring equipment in industrial processes. The 4-20mA current loop is used to transmit data from the field devices to the SCADA system. • Programmable Logic Controllers (PLCs): PLCs are used in many industries to control and automate systems. The 4-20mA current loop is used to transmit sensor signals to the PLC. • Transmitting Sensor Signals: The 4-20mA current loop is a common method of transmitting sensor signals in industrial control applications. It provides accurate measurement and control of processes, such as temperature, pressure, and level. • Remote Data Transmission: The 4-20mA current loop facilitates transmission of data from remote sensors over a twisted-pair cable to a programmable logic controller (PLC) in a control center.

These applications leverage the benefits of the 4-20mA current loop, such as its robustness against electrical noise and its capability for long-distance signal transmission.

Risks, Vulnerabilities and Threats

Given the extensive use of 4-20mA in exposed industrial applications, 4-20mA analog circuits are at risk from overvoltage transient surge events caused by lightning strikes, electromagnetic coupling, and Ground Potential Rise (GPR).

The Cost of Degradation, Disruption and Destruction

Exposure to transient events can cause Degradation, Disruption and Destruction to equipment and operations resulting in expensive downtime and costs of equipment repairs. ABB Motion Services conducted a recent survey of 3,125 plant maintenance managers across the globe and concluded the typical cost of an outage that lasts for an eight-hour working shift is $1m. That’s $125,000 per hour over an eight-hour working shift, which equates easily to the time usually taken to get an operation back up and running when something goes wrong.

Investing in Reliability: Implementation of Surge Protection Strategy

The cost of implementing a comprehensive surge protection strategy is extremely low compared to the potential cost of equipment repair and downtime as revealed in the ABB study. Citel offers a range of data line Surge Protection Devices compatible with 4-20mA.

Recommended Surge Protectors for 4-20mA

Interface	Protocol	Wiring	Max.Operating Voltage	Max. Freq.	Part #	Picture
4-20mA	Analog	2-wire	6Vdc	n/a	DLC-06D3
4-20mA	Hart Protocol	2-wire	6Vdc	2.2 KHz	DLC-06D3

References