The 4TM’s patented plug-on feature and our fully automated manufacturing module provide 4TM customers with the minimum total installed cost.

Quality

Sensata Technologies has designed quality into the 4TM product and process to meet a higher quality standard based on Statistical Process Control techniques. Each 4TM production lot is accompanied by a “Certified Quality Report.”
This document certifies, based on statistical methods, the lot’s compliance with temperature, trip time and other specifications. Supplying certified devices eliminates our customer’s need for incoming inspection of the 4TM.

Performance

The basic function of the 4TM is to protect the motor in a refrigeration compressor from overheating, resulting from locked rotor or running overload conditions. The 4TM provides this protection by sensing the current and temperature of the motor. The fundamental actuation principle incorporates a noncurrent carrying snap-acting disc, which is located above the heater element.
In addition to radiant heat generated from the heater, compressor shell, and ambient, the disc senses the heat from the metal pin carrying line current through the hermetic terminals. When the disc snaps, it actuates the spring arm located above the disc, opening the contact circuit - which shuts off the compressor motor. The operating parameters of the 4TM are not affected by contact wear because the contacts are not part of the resistance circuit and are not part of the temperature calibration mechanism. The patented design features of the 4TM have resulted in the following performance and reliability improvements:

• Longer off-times for better matching and compatibility with PTCR starters
• Better repeatability of trip time and ultimate trip
• Minimum temperature drift versus life cycles
• Excellent resistance to physical and thermal shock
• Meet rotary compressor high side pressure requirements
• Application range – 1 to 5 HP