Water level control with 2 level sensors


Thread Starter


I have a water reservoir with a pump & 2 level sensors - upper & lower. I want the pump to come on only when the water reaches the upper level sensor (obviously at this time the lower sensor is also made) and remain on until it falls down below the lower sensor level. I'm using 2 separate relays.
You can do that with one relay or two. Simplest way is to have both switch points set at N/C. I can’t draw that here – but what you want is the relay to latch on contact with one switch – then – when the other contact is hit is de-activates the relay coil opening the contact.

You also need a snubber circuit as the contacts will burn the reed switch. WE can help you with that by going to: http://www.almegcontrols.com/manual_level_control.htm and looking at reed switch hookup.

Or – you can buy a solid state latching relay with a 240V8A contact and it powers up the level switch at: http://www.almegcontrols.com/latching_relay.htm

If you need a drawing using a relay – email the company for a drawing.

Bob Hogg

Darell Piper

Route the lower and the upper relays to the pump start circuit. Wire the lower sensor to come on when a low level is reached, this will pull in the lower level relay, seal this in with the an aux contact from the pump motor, then wire the upper level sensor to be made when a high level is reached, wire the normal close contact in series with the pump start coil. When a high level is made the relay will energize and shut off the pump.

You will require one of the relays to be dual pole. Lets call the relays A and B.

Relay A (Dual pole) will be triggered by the top sensor and will control the pump and will energize relay B.
Relay B will hold relay A in until the water level drops below the low level sensor.

Connect as follows:
One end of power (+) to one end of the lower sensor.(Assuming that sensor is NO).
Connect other terminal to one end of the top sensor. Also wire this terminal to the NO contact on relay 2. (C)

Connect the other end of the top sensor to the one end of relay A coil.
Connect the other end of relay B's NO contact to the same coil terminal above.

Connect the other end of relay A coil to other end of power source.(-)
Also connect (C) above to the NO contact of relay A.
Connect the other end of this relay A contact to power (-)

Connect the pump to the NO contact of relay A. - (The second set of contacts)

System works as follows:
No water in tank - nothing happens.
As water rises above the low sensor - nothing happens.
As the water rises above the top sensor the contacts close and relay A energizes.
This starts the pump and relay B is energized.
The NO contacts on relay B are now closed and it will be used to hold relay A in when the level drops below the top sensor.
As the water level drops below the low level sensor, relay B will de-energize, and it will deenergize relay A - stopping the pump.

Bill - (http://www.anadexlabs.com.au) - Easy water tank level display and control systems.