Half of PCM Not Working?

[Orion.DeYoe]

Sorry, this might be a bit rambly.

We were working on testing the solenoid valves on our practice robot and none of the valves were firing as they should. We decided to test the competition robot before taking something apart on the practice robot to check every little connection.

The competition robot exhibited the same behavior which is as follows:

We have 4 solenoid valves (24vdc, double acting from automation direct) so there are 8 connections and therefore the PCM is filled up. We used these valves last year on our robot and really liked them.

The valves have a plug connector that comes apart to reveal some screw terminals. These are labeled as "DC -" and "+". We used last year's robot as a reference and noticed that the red wire from the PCM was attached to " DC -" and the black to "+" (opposite of what we expected). The valves worked fine last year so we duplicated the wiring on both robots.

When the robot was powered on, code run, and then enabled, the compressor started up just fine and stopped as it should.

We had several pairs of buttons in our code (we use LabVIEW) that switch global variables between true or false. We set the output of the solenoid in a loop in the "periodic tasks" vi based on the value of the global variable.

Each valve is wired to a pair of ports on the PCM that are opposite from each other (I.e one valve is wired to ports 3&4 and one is wired to 2&5 etc).

During testing, the solenoid halves connected to the 0-3 side of the PCM would fire as expected. The red LEDs on the PCM ports would turn on when that side of the valve was active and turn off when it was not. The trouble came when switching the valve to its other side (the side connected to 4-7 on the PCM). In the initial configuration, no LEDs on the 4-7 side would light up.

We tried reversing (correcting) the polarity of the connections in the solenoid connectors but it had no effect. We made sure the PCM jumper was in the 24vdv position. We reconnected wires to the PCM to make sure they were making contact.

The next thing we tried was flipping the "forward" and "reverse" channels of the valve in code. When this change was tested, the solenoid (we were only testing one out of the four at this stage) side connected to the 0-3 ports stayed powered (the PCM LED stayed lit) even as we actuated the solenoid through our joysticks. The side connected to 4-7 turned on and off as we would expect as be pressed the joystick buttons.

This doesn't seem like a bad hardware issue considering we have two PCMs (one of which was used last year with no issues) and 8 brand new valves exhibiting the same behavior. It seems more like a code issue, but the polarity thing on the solenoids has me really confused.

Has anyone encountered a similar issue? Is there something really obvious that I'm missing? Does anyone have screenshots/pictures of their valve/PCM/LabVIEW code setup that they can share?

[Mark McLeod]

Definitely a code problem.
Ignore the solenoids and work to get the PCM solenoid LED lights to behave properly.
Until your code can trip the LEDs correctly, the solenoids and their wiring aren't even involved.

[Orion.DeYoe]

Originally Posted by Mark McLeod

Definitely a code problem.
Ignore the solenoids and work to get the PCM solenoid LED lights to behave properly.
Until your code can trip the LEDs correctly, the solenoids and their wiring aren't even involved.

So the PCM LEDs are not dependant on the valve solenoid circuit being completed (I.e. the valve doesn't have to be plugged in for that LED to turn on)?

[G_rupp]

No, they are indicators that the switch is working. There is a Simple Solenoid.lvproj xxample in the NI Example Finder. You can see this by selecting Help then Find Examples. This allows you to check the solenoids one at a time. The test has to be stopped and started for each solenoid. While it is running, you can toggle the switch and verify the operation.

[Alan Anderson]

The behavior changed when you changed your program. Show us your Periodic Tasks and we'll probably be able to tell you quickly what's wrong with it, and how to fix it.

Also show us Begin so we can verify that the solenoids are being opened as they should be.