All in a (1/2) Day’s Work
We wanted to share a ‘day in the life’ anecdote from one of our staff engineers, Gene Gallagher. Gene’s process for creating the best and most affordable outcome for our client is a great example of how you don’t always need expensive new machines when something goes wrong. Take it away, Gene!
I received a phone call informing me that a machine that has been running for the past 5 years was no longer running in production.
I know that something must have changed.
The Process: A sensor detects the arrival of a bottle and triggers a cylinder that is forced downward by an air solenoid and places a cap on the bottle. The solenoid then forces air into the cylinder and causes the cylinder to retract and the bottle is released. This is a very high volume system: approximately 1 part per second.
The Problem: 1 out of 10 times, the cylinder would stay in the down position.
- I inspect all of the sensors involved:
- All of the sensors passed the test.
- I observed the outputs involved:
- I saw that the output was changing states (the light on the PLC was turning on and off with the ladder logic).
- I inspected the wires looking for breaks from the output to the solenoid:
- I did not find any breaks.
- I was a bit puzzled and had to go back to basics:
- I know that the solenoid was working.
- I know that the inputs were working.
- I know that the output was working.
- I know that the system was not working.
- I know that the system had been running for 5 years non-stop.
- I pulled out my multi-meter and tested all of my facts:
- I connected the solenoid directly to 24VDC 15 times and the cylinder actuated each time.
- An assistant flagged the inputs and I measured 24VDC from each input.
- I isolated the output and forced a changed in state from my laptop and measured a change of 24VDC. I did this 15 times in a row without fail.
- I reconnected the rest of the circuit and tested everything again. I found that sometimes when the PLC output changed state the voltage did not change.
- I added my new fact to the list:
- The output was a relay output that must be near the limit of its maximum number of cycles, and is suffering from intermittent failure.
- I changed the solenoid output to a spare output and put the system into auto mode.
- I observed 500 parts run in a row without fault.
- I got lunch.
Gene’s department supervisor and company president Shawn Mott was very pleased to hear this account and thought it would be great to share more widely. Our records indicate that Gene did indeed return from lunch and got back to work fixing more stuff!