Temperature Sensitive Switches

High accuracy temperature switches for control and warning systems used in the prevention of overheating in engines, ducts and control equipment, de-icing and air conditioning.

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Our high accuracy temperature sensitive switches are used throughout the aerospace industry for control and warning systems to prevent overheating in engines, ducts and control equipment; for windscreen and wing de-icing and air conditioning. They are available in virtually any form: probes, surface sensors or custom housings – they can even be embedded in windscreens.

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The sensors are capillary temperature switches with mercury or mercury eutectic as the contact medium, with two or more platinum contacts which will make or break at specified temperatures. Monitoring range is –54 to +250ºC as standard, although the lower limit can be reduced to –70ºC with the addition of a heater winding around the sensing element. Heating also allows for anticipatory temperature control and for proportional control as the temperature approaches the switching point.

Hermetically sealing the contacts and the switching medium in a glass capsule ensures complete protection from atmospheric contamination, minimising contact wear. Operational life in a correctly designed circuit is exceptionally long and no maintenance is required. The sensing elements are potted in a silastomer compound to protect against shock and vibration. The unit is pressurised to 10 atmospheres and subjected to a drop test of 100g.

HOUSINGS

A wide range of housings are available to meet individual requirements – existing Approved units or housings designed to new specifications. Enclosures are machined from solid billets (usually stainless steel or a high-grade alloy) which is then anodised or plated, and can be manufactured incorporating interface circuits. Most housings are supplied as probes in various forms: Closed - for liquids or inside pressure vessels. Open- ended with side vents - for detecting air temperature. Sprung tip - for slip- ring or contact sensing. Other types of encapsulation are available for surface sensing or for special monitoring applications.

SWITCH TYPES AVAILABLE

SS Sealed end probe, Screw-in fitting
W Wire ends
SF Sealed end probe, Flange fitting
Terminals
OS Open ended probe, Screw- in fitting
P Plug – connect
OF Open-ended probe,Flange fitting
R Proprietary connector
CO Clamp On probe, button sensing
ST Sprung Tip probe

Switches will operate a lamp directly ensuring an instant warning of temperature changes, however, due to the sensitivity of the platinum contacts they can only handle small loads. For control purposes the load should be under 10mA (with suppression in the circuit), or up to 250mA in warning circuits, both at 28V DC. Filament lamps should have a shunt circuit to avoid damage due to inrush currents.