Jerguson's Tri-Magnet Switches replace mercury-based level switches
Plants can now retrofit their mercury-based level switches with the economical and environmentally friendly Jerguson Tri-Magnet Switch from the Clark-Reliance Instrumentation and Controls Group. Replacement kits are available to upgrade a variety of mercury switches, enabling replacement of the switch and enclosure without removal of the existing chamber.
In operation, the float or displacer drives a stainless steel sheathed permanent magnet attached to the float rod in the glandless pressure tube. As the float rises and falls with the changing liquid level, the float assembly moves upward inside the pressure tube. A switch mechanism mounted inside the enclosure adjacent to the pressure tube is activated by the rising or falling magnet.
The vertical movement of the float magnet in the pressure tube simultaneously actuates the secondary magnet and the switch magnet within the switch mechanism to operate the contacts. This three magnet system enables the float magnet to pass the switch and actuate switch mechanisms at other levels. Switch mechanisms that are actuated will not reset until the float magnet actuates the switch mechanism on a falling level.
The switch mechanism is based on a Jerguson three-dimensional magnet design in which the snap action is accomplished by the utilization of magnetic repulsion. The magnet mounted on the float rod causes the secondary magnet to rotate as it passes up and down. The switch magnet is repelled by the secondary magnet and snaps to the opposite side. This causes the cradle to pivot, moving the push rods that operate the switch contacts. The result is positive snap action interlock switching.
Four different switch mechanisms are available. A 10-amp mechanism is designed for general-purpose duties up to 480°F. For high temperature applications up to 750°F and 5 amps, a high-temperature mechanism is offered. Hermetically sealed switch mechanisms are suitable for low-temperature duties, contaminated atmosphere environments and intrinsically safe circuits. All moving parts and contacts are enclosed in an inert gas filled stainless steel enclosure. Low-current mechanisms are gold-plated contact switch mechanisms for use in intrinsically safe or low-power circuits up to 750°F.