WorldWide Drilling Resource

40 JUNE 2018 WorldWide Drilling Resource ® Monitoring Temperature with Thermal Switches Adapted from Information by Control Products, Inc. Almost every large commercial machine with an engine or motor has a system for monitoring temperature. System fail- ure, or the need to deliver cooling fluids to critical systems can be prevented by using thermal control switches, which are designed to shut down or throttle operation. These switches are trusted to prevent compromised safety situations which can harm machines or workers. Thermal switches are completely self-contained temperature detection and switching devices capable of precise operation at high temperatures. They can han- dle high current switching applications without requiring an external control system. Since thermal switches offer a straight-forward approach to shutting down a system if a critical temperature is reached, they are specified as cut-off switches. Designers are drawn to the concept of an electromechanical temperature switch because of the device’s simplicity, which requires no power to operate. Since these switches have many unique applications, an uncompromising approach in the design process is needed. Thermal switch products are specifically designed to withstand extremes of heat, dust, moisture, wind, sand, and vibration to allow them to be reliable safety controls in a wide variety of oil- field, mining, and construction equipment. Some thermal switches achieve contact movement by using a bimetallic snap disc. Snap action provides shock and vibration immunity, as well as a broader temperature differen- tial. Switch configurations include surface mount without probe, surface mount with probe, thread mount, clamp mount, hermeti- cally sealed, and dual set- point. The vari- o u s sw i t c h appl icat ions include over- temperature on a i r com- pressors, distilling machines, food extruders, escalators, engine coolant, and elevators. Bimetal device switches are slow make-and-break devices, which provide tight tolerance temperature sensing over a small range. They come in a wide variety of forms such as solder ter- minals, glass-sealed connectors, with integral wire leads, and with dual setpoints. They are used extensively in wind tur- bines, aircraft, plastic extruders, and various military vehicle systems. The rod and tube switch operates by utilizing differences in the expansions of two materials - the rod and tube. The external tube is the high expanding element, so these products offer outstanding response times. Applications include aircraft engine over-temperature, refinery process control, railroad switch flame detection, stack scrubber temperature monitor- ing, turbine exhaust monitoring, and brake over-temperature indication on large construction equipment. Bimetallic snap disc, bimetal device, and rod and tube. Thermal switches. C&G