Using a Logic Relay as an Irrigation Controller

Basic Requirements for a simple irrigation controller.

The Logic relay is required to monitor the start input, a low pressure switch, a high pressure switch and a low water switch.

When a start is called, the logic relay checks the low water switch, Low pressure switch and high pressure switch.

For a period or time after the start, the low pressure switch is bypassed (ignored) to allow the pipe line to fill.

If the low water swithc indicates a low water state, the start is inhibited and a low water trip occurs.

If the High pressure switch indicates a high pressure, the start is inhibited and a high ressure trip results.

Once the low pressure bypass has timed out, a low pressure state causes a low pressure trip.

All trip inputs have a programmable time response delay to prevent trips caused by pressure transients.

The start input is normally open. A closed circuit on the start input causes the pump to start and run.

The protection inputs, (pressure and low water) are closed for normal operation and open for a trip state. If a wire gets broken, the starter trips.