When Bi-Metal Thermal Switches Are Really The Only Good Solution

SnapStat Thermal Cutoff Switches

In an era where many applications have gone the way of cheap remote sensors and electronics, there is still a place for electromechanical bimetal switches that is cost effective, reliable and in some cases the only solution to complex operational requirements.

Thermal switches are often specified as cut-off switches because they represent a straight-forward approach to shutting down a system if a critical temperature is reached. The simplicity of an electromechanical thermal switch is what makes this approach so desirable to designers, as they are passive devices which require no power, and will reliably change state at the specified set point.

There are some Key attributes to consider when trying to understand whether a bimetal thermal switch is the right choice for your application.

  1. Will a passive sensor handle the temperature range required?  Our Rod & Tube series can go up to 1750F, a temperature that would melt many other kinds of sensors.
  2. Is the operating environment stable?  Sensors tied to control systems may be more sensitive to local factors in the system such as vibration, EMI, current or voltage limitations, response time, etc…
  3. Is your system self contained or does it maintain remote operational control?  Remember that thermal switches actually achieve an open or a closure when a programmable set point is reached. Sensors generally have to have their output calibrated and monitored to determine temperature and then separate commands are sent to other electronics to achieve contact closure.
  4. Are you budget or form factor limited?  CPI thermal cutoff switches come in a wide variety of mounting options including custom designed variations.

In general, the more demanding your environment, the more likely you are to be considering a self-contained bimetal thermal switch.  You would not be alone.  See below for a list of applications that have gone the way of bimetal thermal for a variety of reasons.

  • Plastics extruder barrel overtemp detection.
  • Brake overtemp indication
  • Engine cooling fan control
  • Clutch overtemp in escalators
  • Bleed air overtemp indication on aircraft environmental control systems
  • Window defrost overtemp on military vehicles
  • Overtemp detection in oil refinery processes
  • Avionics overtemp inside the aircraft avionics bay
  • Gas shut-off  flame detection on railroad switch de-icing
  • Flame detection in aircraft engine

CPI Is a World Recognized Expert in the Design and Manufacturing of Thermal Limit Switches

CPI produced its first thermal switches for the military in 1946 and has continued to provide these switches into military and commercial markets where only the toughest parts need apply. If you have an application tough enough for our parts, do give us all, we’d love to hear about it.