Determining If Relays Are Working, Programmatically

Projects General Guidance
1

Maybe I am overcautious, but I would use an Arduino Mini to determine if a set of three relays is operating properly. It would seem logical to use analog inputs on each side of the relays and make a comparison between In and Out. Can anyone see any problems with that, electricity-wise, or Arduino-wise?

2

Hi, you can use a mini to monitor relay operation, but how you do it will depend on the type of relays.

  • Coil Voltage, AC or DC
  • If relay has extra set of unused contacts that can be used to monitor condition

If each relay has a set of unused contacts you can use those as input to the mini to directly indicate if relay ON or OFF, it will also show relay mechanical failure.
If not, then monitor the coil voltage using opto couplers.

Tom..... :slight_smile:

3

What's switching on the contact side of the relays?

4

What voltage is on the contacts ? Doing analog comparisons using current limiting resistors and analog switches or op amp comparators is possible but why would you want to go to the trouble ? (what makes you so cautious ?)

5

analog inputs on each side of the relays and make a comparison between In and Out. Can anyone see any problems with that

Yes, if you are talking about the coil it doesn't tell you much at all, and if you are talking about the contacts you would never read the voltage drop as it will be uV probably.

It will depend on exactly what you are switching, using a spare contact pair is the easiest way but that's still not 100% as the other contacts may have a fault.

What are you switching?

Rob

6

if you are talking about the contacts you would never read the voltage drop as it will be uV probably.

There you go. That means it's working if the two samples match. If one is 12Vdc and the 0V then there's a problem.
If both are high or both are low then your good to go. This is the Exclusive -OR function. If both are high or both are low, output is low. If EITHER input differs from the other , output is high. 12V CMOS 4030 Ic.
http://www.cmos4000.com/functions/exclusive-or.html

7

If one is 12Vdc and the 0V then there's a problem

Doh, don't mind me, I've only had 2 cups of coffee and aren't fully up to speed yet :slight_smile:

In fact I used an XOR gate to do almost this exact function (detect a blown fuse) just recently.

Rob