Monitoring doors opening with a Sensatronics E4

So you thought that the Sensatronics E4 could only be used for monitoring temperatures ? Think again. With a relatively simple hardware addition the unit can monitor the opening and closure of doors with a standard magnetic door closure switch.

 Interested ?

 Well first the technical info

If you simply plug in the door closure switch to the terminals where you would normally plug a temperature probe – you won’t get the results you are looking for. In order to do that we need to bring the max and min values reported by the E4 into a range that doesn’t think you are reading a faulty temperature probe. We achieve this by using a pair of resistors – one in series and one in parallel to ensure that the E4 always “sees” an appropriate value when the door switch is open or closed.


And now for the practical

You need the following items –

 a piece of terminal block – with two sets of screw terminals

two resistors rated 47K Ohm and 10K Ohm

 a piece of insulated wire and

of course an E4. 


I used a terminal block with two sets of two terminals cut from a full run of terminal block – a single insulated wire and a 47K ohm res in parallel and a 10K ohm res in series. The yellow lead from the door switch is connected to terminal one with the 47K crossed on the terminal block. On the other side a simple wire connects to terminal one of the probe connection you are using on the E4.

The red wire is connected to the other terminal of the terminal block and then the 10K res is connected to the other side of this terminal on the terminal block and thus into the E4. (obviously the colours of the wires in your door switch cable will vary – try one way and if nothing swap them over at the terminal block)

Now for testing  – close the door switch – put an elastic band or tape to hold it closed. Open the status page from the web interface on your E4. If you are not getting a value which was higher than when nothing was connected to the probe terminals – check your wiring. However if you are getting a value – note it and then open the switch. Note the new value.

In my case this gives values of 40.8 degrees open and 50 degrees C closed. – A simple temptrax monitor on my Intellipool software picks up that signal and alerts. The min / max values for the probe are 48.0 and 52.0 (obviously the upper limit will never be exceeded so it will always show okay) – the  “open” value of 48 degrees is just an arbitary figure i.e anything less than 50 approx should do.