Thursday, July 25, 2019

Electromechanical Relays (EMR) Pros (Advantages)
  • Lower initial cost compared to solid state relays.
  • Provides complete electrical isolation.
  • Tolerates high current & voltage transients.
  • Insensitive to electromagnetic interference (EMI) / radio frequency interference (RFI).
  • Higher open resistance (air gap).
  • Lower closed resistance.
  • Available with many poles/circuits (up to 8 or more).
  • Many different circuit configurations available.
  • Multiple packaging & feature options.
  • Most typical failure mode is open.

Electromechanical Relays (EMR) Cons (Disadvantages)
  • Higher control (coil) power consumption.
  • Contact arcing can cause pitting & eventual open/short failure.
  • Contacts can be affected by corrosion, oxidation or contamination.
  • Contact bounce possible due to shock & vibration.
  • Generates electromagnetic interference (EMI) / radio frequency interference (RFI).
  • Can be orientation sensitive.
  • Can be affected by external magnetic fields.
  • Subject to mechanical degradation over time (residual magnetism, armature flexing, spring stretching).
  • Potential higher overall cost over equipment life.
  • Can be noisy.

Solid State Relays (SSR) Pros (Advantages)
  • Substantially longer life compared to mechanical relays.
  • Low control power consumption.
  • Faster on/off cycling.
  • Allows very fine proportional output control.
  • No arcing (safer in hazardous environments).
  • No contact bounce.
  • Not orientation sensitive.
  • Switching not affected by shock & vibration.
  • Not affected by external magnetic fields.
  • Less electromechanical interference.
  • Silent operation.
  • Allows many functions in a single package.
  • Potentially lower overall cost over equipment life.

Solid State Relays (SSR) Cons (Disadvantages)
  • Higher initial cost compared to mechanical relays.
  • Generate more heat compared to mechanical relays.
  • Current rating may require derating based on ambient temperature.
  • Voltage or current transients can damage or affect operation.
  • Susceptible to electromagnetic interference (EMI) / radio frequency interference (RFI).
  • Lower off state resistance.
  • Higher on state resistance.
  • Most are single pole/circuit (some available with up to 4).
  • Normally closed/ON function available on a limited basis.
  • Changeover form/circuit not supported.
  • Most typical failure mode is shorted/closed.

A solid-state relay (SSR) or solid-state contactor (SSC) is an electronic component that switches power (AC or DC current) to a load circuit and provides electrical isolation between an application’s control circuit and load circuit. It is a competitive technology to electromechanical relays (EMRs) and other switching technologies such as mercury displacement relays (MDRs).

Why use solid state switching technology?
  • Long service life
  • Quiet operation
  • Minimum electrical noise
  • Low power consumption
  • Shock & vibration resistant
  • Ideal for harsh environments
  • High compatibility with control systems
  • Reduced weight
  • Position insensitive
  • Fast switching
  • Magnetic noise immunity
  • Reduce energy cost
Solid state relays & solid-state contactors applications

Although there are literally thousands of individual uses for solid state relays and solid-state contactors, most can be categorized into the following applications:

Heating control application

This encompasses the largest segment of solid-state relay users.

Applications include, but are not limited to: professional food equipment, plastic molding/extrusion machinery, heating ventilation air conditioning & refrigeration (HVAC&R) and soldering equipment.

Benefits include: Long life, no maintenance, safe product, easy to interface, as well as enabling temperature accuracy. Suitable for heaters, fans, blowers and valve control.

Motion control applications

Applications include, but are not limited to: elevators, lifts, hoists, exercise equipment, conveyor
systems, solar trackers, fans, solenoids and valve control.

Benefits include: Endurance, shock & vibration resistance, soft start, reversing, no arcing, fast switching, long life, no maintenance, easy to interface, reduced parts count.

Power control applications
Power applications cover switching of power supplies, transformers, regulators, inverters, converters, UPS systems, etc.

Benefits include: Easy to interface, no arcing, immune to magnetic noise, automated switching,
low electrical noise, no maintenance, shock and vibration resistant.