When Sensors Make no Sense

Thermal switches were originally designed to be reliable, standalone, systems that encompassed both a sensing element, and a switch. At a chosen set-point these thermocouple devices would reliably close or open a contact allowing for critical systems to be protected or activated. They were very accurate, could detect at very high temperatures, could handle a good amount of current in their switches, and did not require intervention by operators or other control computers or systems. They were/are completely standalone control systems.

But the cost of producing and deploying thermal switches, along with evolution of computers and small thermal monitoring devices, inevitably meant that some applications for which thermal switches were the only game in town, would eventually go the way of sensors and remote computer control.

Yet there are still two camps out there on this idea of sensors vs. switches, even within the same applications. Some engineers would not consider using a sensor while others don’t have the reliability concerns and are happy to enjoy the lower cost of pure sensors connected to controls in their application. How does a good engineer sort it all out?

When it Might Be Time to Consider Thermal Switches instead of Sensors

While the value of sensors in many applications comes down to cost and sometimes size, there are still a number of reasons that engineers may prefer standalone thermal switches in their applications.

  1. Temperature RangeTemperature Switches like the CPI Rod & Tube series can reliably switch up to 5A of current at temperatures up to 1750F, long after your sensor has converted its mass into energy. (ie. melted)
  2. Reliability – In applications like aircraft ECS (Environmental Control System) we have seen our thermals deployed as a fail-safe backup to sensors, to insure local thermal limits are not exceeded in the case of sensor or computer failure.
  3. Independent Operation – Thermal Switches do not require controlling electronics or independent monitoring to perform their switching operations. The switches operate reliably as a self contained switching unit making them idea for fail-safe applications.

CPI Thermal Switches

CPI makes three distinct lines of thermal switches, organized around the temperature ranges they serve. All represent hardened thermal implementations cultivated over a 70+ year period of field deployment in every imaginable environment, from jet aircraft, to plastics manufacturing, to submarines.

  1. SNAP STAT – (0F – 300F) Using a precisely engineered bimetal snap disc, we actuate a miniature microswitch through a double snap action. Multiple mounting options available.
  2. PLUG STAT – (0F 650F) Contact movement in the PlugStat is achieved by controlling the different expansion rates of 2 fused metals providing tight tolerances and a small differential.
  3. ROD & TUBE – (0F – 1750F) Ideal for use in galley’s or furnace controls to sense or control combustion. Very high temperature sensing with very rapid response time.

For more information on Thermal switch solutions for your applications, call CPI today.