When to use a Real Thermal Switch not a Sensor

When CPI started making thermal switches for the Military in the 40’s, there really wasn’t any other choice. Thermocouple based switches with variable set-points and various temperature ranges of operation were made using the thermocouple materials of the day, mostly copper, aluminum, and chrome. The concept of a thermocouple had been around for over 100 years but CPI switches of that time stood out because they provided reliable operation over an extended temperature range, in an environmentally hardened package suitable for battlefield conditions.

Temperature switch technology has evolved over the last 75 years however, and depending on what you’re trying to do, alternate thermal switching technologies abound. For instance, in applications where smaller temperature differences need to be measured with high accuracy (like from 0-100C at 0.01%), technologies like thermistors, temperature sensors tied to external control systems, or simple resistance thermometers may be more suitable and cost effective.

CPI Rod & Tube Thermal Switches

CPI Rod & Tube Thermal Switches

Still, traditional thermal switches have evolved too. The variety of types, and use of metal alloy’s has been informed by discovery, experimentation, and improvements in manufacturing processes. Today’s CPI thermal switches come in three basic types, covering a thermal range from 0 to 1750 degrees Celsius. And as always, CPI switches maintain their hardened design making them unique in the world for their electromechanical endurance, and their survivability.

Thermal Switch Applications

Perhaps one of the best ways to understand the applications that are better suited for thermal switches vs. sensors is to look at common applications for these switches.

Galley Temperature Sensors – Prevention of galley fires is critical on both Navy Ships and around any high temperature professional cooking stations. With flash points over 1000 degrees, these systems usually do not have a controller and so local switching to turn of gas supply or raise an alarm is appropriate.

Steel Manufacturing – Thermal Switches are used extensively in the steel and iron industries to monitor temperatures and chemistry throughout the steel making process. Disposable, immersible, type S thermocouples are regularly used in the electric arc furnace process to accurately measure the temperature of steel before tapping. The cooling curve of a small steel sample can be analyzed and used to estimate the carbon content of molten steel.

Engine Cooling Fan Control – Thermal Switches are commonly used to locally control cooling fans which prevent engine overheat on everything from generators to jet engines.

Gas Shut-Off – In systems using pilot lights, a thermal switch will often sense the presence of the pilot and shut off gas flow if the pilot should go out for any reason.

Oil Refining – Control of temperature in the oil refinery requires accurate and hardened thermal sensing for many fail-safe systems in the refining process.

Avionics Bay Over-Temp – In both commercial and military aircraft, ambient temperature in the avionics bay can reach well over 100 degrees C as components heat up, contributing to early system failure.  Thermal switches are used here to economically activate cooling systems.

CPI Thermal Switches

Our three lines of thermal switches include the following.

  1. Snapstat (0 – 300C)
  2. Plugstat (0-600C)
  3. Rod & Tube (0-1750C)

All switches are characterized by flexible mounting options, highly accurate and programmable set points, and hardened construction for extreme environments.

For more information on CPI thermal switches, please contact our engineering team today.