Partial Switching Outputs

[stuart464263]

Our customer has a 6527 I/O card running via a SCB100 interface.

One of the outputs is wired to a door interlock solenoid. Using the instructions Port 3:3, HiZ / Port 3:3,LoZ in his sequence we are measuring the voltage to the solenoid as 0 and 12V despite having a 24V supply on the + terminal of that port. We have checked various voltages and can confirm that everything is intact (eg, 0V on the other side of the solenoid is okay.) The solenoid rating is well within the specification of the solid state relays of the 6527.

Another output is correctly driving a solenoid valve 0V/24V.

We have tried moving to another output with the same result. To our understanding, the solid state relays should either be fully off or fully on, so we cannot see how we can be getting a half-output!

Although the door interlock is currently releasing, it is on the limit of its reliability, and we need to advise the customer how to rectify the problem.

[johnsold · Accepted solution]

While I have never used that device, half voltage behavior is often an indication that something is drawing too much current.

1. I do not recall seeing a door interlock solenoid with a current rating below 120 mA. Very small door?

2. Is the 24 V supply AC or DC?

3. Have you measured the resistance of that solenoid? If it is an AC solenoid, measure the current with the plunger in various positions. AC solenoids with the plunger not fully seated (due to mechanical obstruction or misalignment) can draw huge currents.

Lynn

[stuart464263]

Thanks Lynn,

You're quite right. I just tested a spare and found it's 240mA (ohm's law doesn't quite work). The machine's been running for 9 years like that! I'll have to get the customer to fit an interposing relay.