Swichgage® is the registered trademark on FW Murphy's best known line of instrumentation. As the name implies, a patented visible and adjustable wiping electrical contact, or switch, is added which combines monitoring, control and automation all in one simple instrument.
The switch is set to trip when temperatures, pressures, or other variables measure above or below acceptable levels. When the switch trips it activates an alarm and/or a shutdown device, thereby helping you protect your engines and equipment from damage. These electromechanical control devices offer easily adjustable, single-pole contacts or snap-acting SPDT switches.
In 1940 Frank W. (Pat) Murphy started building and distributing the "Guardian Safety Switch", which was originally designed to protect oil pipeline pumps. In the early 1960's the "Safety Switch" was officially renamed the "SWICHGAGE®". Over the years, many minor adjustments were made to original design in order to accommodate different applications and markets.
On a Swichgage®, such as Murphy's 20P-100 pressure gage shown to the right, the gage indicating pointer acts as a pressure indicator and as one switch pole which completes a circuit when it touches the adjustable limit switch contact. The contacts are grounded through the Swichgage® case and have self-cleaning motion to ensure electrical continuity.
Engines have life signs, such as pressure, temperatures, levels, and overspeed conditions. These vital signs can be monitored by a Swichgage® instrument which constantly monitors pressures, levels, vibration, temperatures, and overspeed conditions and activates alarm and/or shutdown when preset limits are reached. These protective instruments override the normal operation, shutdown the engine, and lockout further automatic operation should failures occur in any of the protected functions.