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Fluid pressure acting against the diaphragm causes the cantilevered (moving) contact blade to deflect. The amount of deflection is a function of contact thickness and pressure. The moving blade deflects until it contacts the points of the adjustment (fixed) blade, completing the circuit. The relative position of the blades can be changed with an adjustment screw.
In a pressure switch, the medium is connected to the side of the diaphragm opposite the contacts (see drawing at right). As pressure rises, the diaphragm is pushed against the moving contact blade. In a vacuum switch, the medium is connected to the same side of the diaphragm as the contacts. As vacuum increases, the diaphragm is drawn against the moving contact blade. In a differential pressure switch, the medium is connected to both sides of the switch. The diaphragm is either pushed or drawn, depending on the changing differential between the two pressure (or vacuum) sources. Because there are no sliding or levering parts, as with a snap-action switch, the MPL 500 Series switches have virtually no "deadband", or on-to-off mechanical differential. |
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Fluid pressure acting against the diaphragm causes a guide disk to push against the actuator button of a snap-action switch. The disk has a stop to prevent overtravel of the actuator. Adjustment of the setpoint is provided by an adjustment screw and compression spring, acting against the force of the diaphragm. Because of the action of the snap switch, the MPL 600 Series switches do have a "deadband", which many designers utilize in their circuit logic. |
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Mechanically, the MPL 9370 is similar to the MPL 600. However, the snap action switch is built into a specialized housing, which allows pressure, vacuum, and differential configurations around an oversized, more sensitive diaphragm.
The above switch is shown in a vacuum configuration, with one diaphragm. By adding another diaphragm above the switch contacts, the switch can operate in pressure or differential mode. |
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