Measuring and Monitoring Relays Application Guide

By Omron Automation.

Measuring and monitoring relays are like automobile assurance. Even if you are careful, car accidents will occur. Even if you are careful with motors, malfunctions will occur. There are many kinds of car insurance in preparation for a car accident, for people, for objects or for your car etc. There are many kinds of measuring and monitoring relays in preparation for the motor malfunctions, overload, upper & lower current and voltage, phase sequence & phase loss, current leakage etc.

Various machines operate at production sites. Such industrial machines are used as the power source for motors and heaters on production lines, so when there is some kind of trouble with the machines, defects occur in products and sometimes production equipment is damaged. Monitoring the status of the main power circuits for industrial machines and production equipment and protecting devices from low-voltage, over-currents, over-voltages, and other faults for power up to 600 VAC in this way is called device protection. OMRON calls the products for this type of device protection measuring and monitoring relays.

OMRON K8DS-PM2 Measuring & Monitoring Relay
OMRON K8DS-PM2 Measuring & Monitoring Relay

There are various types of measuring and monitoring relays depending on what they monitor and output alarm signals for. The basic functions are to receive input signals, monitor and determine them, and output an alarm signal if a set value (threshold) is reached. Measuring and monitoring relays (alarm relays) protect your important devices and products against unlikely problems (e.g., overvoltage and over-current faults).

They monitor AC power supplies (voltage and current), temperatures, and other analog signals and detect abnormalities in machines and equipment by determining values against alarm thresholds. Also, an alarm signal can be output from relay contacts if an input signal goes into an abnormal status to stop the machine or equipment before it is damaged.

Measuring & Monitoring Relay Operation Example
Measuring & Monitoring Relay Operation Example

There are various failure types that lead to motor failure. By detecting abnormal signals and using them to stop the motor, motor failure and damage to the motor’s load can be avoided. Major examples of motor failures and products that can be used to detect motor abnormalities are introduced.

Phase-loss Errors

  • Welded contacts inside a breaker
  • Disconnection (Wheels rolling over or people stepping on lines, Cables bent too far, etc.)
  • Loose screws (contact failure in wiring)
  • Phase loss inside a motor

Reversed-phase (Phase-sequence) Errors

  • Incorrect wiring (Movable equipment, Incorrect phase on power line side)
  • Reverse rotation of motor will damage valves in pumps.


  • Caught foreign matter (Caught foreign matter locks up the motor)

Current Leakage

  • Insulation deterioration (Aged deterioration, Deterioration due to oil or water intrusion)

Application Examples

  • Monitoring phase sequence/phase loss for escalators
  • Battery voltage checking
  • Protection against idle running of a submersible pump
  • Bulb burnout detection
  • Monitoring the control power supply at communication bases
  • Monitoring compressor power s
  • Monitoring voltage generated by wind-powered generators
  • Monitoring generated voltage

No matter what measuring or monitoring function is needed – physical or electrical – OMRON protects your equipment and ensures processes run smoothly. OMRON relays are designed to detect overloads, temperature, liquid and other potentially damaging fluctuations. Choose from a large range of products that provide reliable protection, cost savings and maximum availability for processes and equipment. No matter what the environment, OMRON’s high quality products are built and tested to give you uninterrupted monitoring.


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