Monitoring solenoid health 4

[CGSmith]

We have several electro-mechanical actuators with fail safe brakes which release using the solenoid. If the solenoid doesn’t release the brake, the actuator won’t work and hatches/doors won’t open. I’d like to find a way to monitor the solenoid coil when the actuators are not in use....they sit for a long time. It is important that they work when commanded. Anyone have experience with techniques or products that monitor solenoid coils? Thanks!

 

[BrianE22]

A little off the wall, can you add some extra stroke to your solenoids? - position them so there is dead space before they actually do what they are supposed to do. Then move them (with small current) through the dead space and record the inductance change. If they appear to be moving through the dead space then at least they are probably not mechanically frozen.

 

[crshears]

Nice, Brian E22! Perhaps what you suggest, performed, say, once every hour, combined with constant "circuit closed" monitoring [ à la breaker trip circuit monitoring ] might serve.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[CGSmith]

Thanks everyone! Update...I've gotten back some information from the company referenced earlier (PRETECH). This looks like the easiest solution....basically turn key. The engineer explained that their Solenoid Coil Monitor works by sending a small ac current through the wire and solenoid at all times. By doing this, it can pick up differences in inductance/resistance even if the resistance of the coil is very low. Then, it has an internal relay that switches over to power the solenoid with whatever voltage you provide. I looked at the Productivity 2000 as well but the output ratings were too low (0.25A) and I don't think this one detects for short circuits.

We've worked it into our design and so far the customer is happy....meets their requirements. This was the wiring diagram of the unit used. The only down side is you have to provide 12Vac. Thanks for all of the help and interesting discussion!

 

[zappedagain]

VEIBLL - Early in my career I designed a cute little diagnostic circuit that could multiplex about 8 different power supplies and verify they were okay. My systems engineer saw it and asked "can't you just make the supplies more reliable?". Sometimes yes, sometimes no. He was a smart cookie. VP for another company now.

Z

 

[VEBill]

Military systems are often required to provide CBIT (Continuous Built-In Test), perhaps with extremely high fault coverage. Needless to say, circuit complexity increases.

Monitoring power supplies can be relatively straightforward. As a more extreme example, signal processing systems might need to time-slice in test signals for end-to-end test, without interrupting normal use at the same time.