Bi-Metal Thermal Switches

Product Announcement from Control Products, Inc.

Bi-Metal Thermal Switches-Image

These small, lightweight thermal switches are ruggedly constructed to maintain stability of calibration even under extreme shock, vibration, and other severe environmental conditions. They can be used as temperature controllers, safety cutoffs for equipment protection and indicators of overheat conditions.


· All welded stainless construction

· Glass hermetically sealed connector (Types M and R)

· Specific bimetals can be selected for maximum sensitivity

· Inconel X springs insure high temperature repeatability

· Platinum Iridium contacts provide excellent arc erosion protection and constant contact resistance

· Special glass insulators are used for thermal and electrical isolation

· M-1 and M-2 switches use calibration screws, which have a special helicoil insert for extra vibration resistance

Factory calibrated. CPI bimetal thermal switches are factory calibrated at any temperature within the range of 0°F to 650°F (depending on type). They can operate in ambient temperatures from -65°F to +700°F and show excellent resistance to momentary overshoots. Drift free performance is assured throughout their long life.

Immune to problem environments. Hermetically sealed (Types L-1 and L-2 are environmentally sealed) for total protection against the effects of moisture, sand and dirt, these bimetal thermal switches are also designed to withstand severe shock and vibration with no shift in calibration. They meet or exceed the requirements of MIL Std. 810.


Bimetal switches are based on a two layer alloy leaf, which deflects with changes in temperature. The heat producing the thermal action works through the bimetal leaf mounting in the top of the probe, and enables CPI to design relatively short probe switches with a high degree of accuracy. The outline drawing shows a close-on-rise unit below the closing temperature. This unit has the bimetal so installed that deflection caused by a rise in temperature goes in an upward direction. This deflection causes the insulating glass ball to release the spring and close the contacts at the predetermined temperature. The temperature has been set by turning the calibration screw to ensure contact closure at the desired temperature. Bimetals are available to produce sensitivity in the desired calibration range while still permitting extreme temperature overshoots and undershoots.


CPI bimetal thermal switches perform reliably in demanding aircraft applications such as: environmental control systems, hydraulic systems, helicopter gear boxes, generators and bearings. Industrial equipment applications include sterilization equipment, plastic extruders, medical equipment, heavy duty air conditioning units, hydraulic activator overtemp, journal boxes, gear boxes, truck drive trains, piped liquids, solders and vehicle coolant temperature control.