Alternative Correct Indicator Wiring

There is no requirement for a fully-closed indicator to light up when a gate is CLOSED. It is just as reasonable for it to light up when the gate is OPEN. In the 3-dimensional model to the right, the "CLOSED" indicators for the diverter gates are replaced by "OPEN" indicators (OP), which light up green as soon as the gates crack open. The icon next to the model behaves the same way as it did when the model used "closed" indicator lights This model functions the same as the previous model in all other respects. Try operating it.

For an indicator to light up when its gate opens, it must be wired to the NORMALLY CLOSED (NC) contacts of the limit switch, which break the circuit when the gate hits the switch's actuator arm, instead of the NORMALLY OPEN (NO) contacts. A type of limit switch with normally closed contacts is used on your refrigerator door to turn out the light inside when the door is closed.

The normally closed contacts are important for safety reasons when a gate is driven by an electric motor. They remove power from the motor when the gate reaches its limits of travel in either direction, so the motor doesn't burn up trying to drive the gate through a piece of steel or throw the gate out onto the floor. When a gate is driven by a pneumatic cylinder there is no need to cut power. In fact, if power to the air compressor is lost, the system will lose pressure and the gate can drift out of position.

The placement of a fully-closed limit switch is critical. If it is too far in, the gate will hit the side of the chute before it hits the switch, so it can pop circuit breakers or overheat. If the switch is too far out, the gate will never close completely, and grain can leak into the wrong chute.

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