Switch Using Multiple Relays

A more complex switching operation may need the use of more than one relay to perform the task.  In this case we will look at using two relays to switch a single item.  Our example will be switching an irrigation system and we have two criteria to meet before we want the water to flow.

For our example we will use a 2-channel ProXR Lite board.  This board has two relay and eight Analog to Digital inputs onboard.  We will connect sensors to the inputs and have them control the relays. 

First we have the basic need that the soil needs to be dry before we switch on the irrigation system.  We will then put a moisture sensor in the ground and connect it to input 1 on the board.  In our programming input 1 will switch relay 1 when the soil is at a certain moisture level (dry).  The second need we have is that we don’t want to irrigate in the heat of the day.  We will connect a light sensor to input 2 of our board and program it to switch relay at dusk. 

As you can see by the diagram, both relays will need to be energized to trigger the light or irrigation in our example.  The electrical signal will come into the common and when the arm of relay 1 swings to the NO side (the moisture sensor activates) it will allow the signal to now flow to the common of the second relay.  When the light sensor in our example says it’s the correct darkness it will swing the arm to the NO position on Relay 2 and allow the signal to activate the light or irrigation.

This example is for irrigation but it can be used in many different applications where your switching is controlled by multiple variants using automatic or manual mechanisms. 

To achieve this we have a couple of options available.  You can purchase a 2-channel computer controlled relay and write the program yourself.  you can find these on our site at: http://www.relaypros.com/Relay/Relay/CAT_RELAY2.  Another alternative is to purchase a Reactor Relay which operates from the sensor inpurts.  You simply configure where the trigger points will be with no programming involves.  You can find the 2-channel Reactor boards at: http://www.relaypros.com/Relay/Relay/CAT_RELAY2_REACTOR.