Pressure sensor trouble

[iv1777]

Our pressure sensor to cut off the compressor at around 120 psi isn't working.
We've tried another sensor with the same problem. We don't know what is wrong because prior to this day it was working fine. Programming and pneumatics brass parts configuration havent changed, neither has the wiring.
The wire looks fine and we have tried another one, too.
What could be wrong??

[ebarker]

two debug steps, do both,

step 1) disconnect the wire from the pressure switch

step 2 - verify control system) start the machine, enable the robot/cRio, and take the two stripped bare wires that were connected to the pressure switch and touch them together. the compressor should cycle on/off as you close/open the two wires. if it doesn't then you have a control system problem.

step 3 - verify pressure switch) connect an electrical meter in resistance/continuity mode to the pressure switch. start the compressor and watch the pressure gauges and meter. as the pressure passes 115psi the continuity should change on the meter. this will verify the pressure switch. make sure to wear safety equipment, monitor the pressure, and think. the relief valve should relieve at 120 psi. if you go past 125 psi vent the system down, turn it all off, and inspect the relief for safety.

basically you need to decouple the switch and control system and test independently.

[iv1777]

Alright. We tried a different valve, and checked the resistance and that is working right.
Tried a new wire, checked for continuity on all connections, the wire is fine.
Wired it up, still nothing!
The compressor's relay light on the sidecar is always green, so it's not getting that signal at all.
I suppose the connection on the sidecar itself could be bad, I will try a different one...
Meanwhile, any other problems you all can think of?
Oh and I tried touching the wires together and it DID WORK so I guess sidecar shouldn't be a problem

[ebarker]

Oh and I tried touching the wires together and it DID WORK so I guess sidecar shouldn't be a problem

so you are saying touching the wires together / un-together definitely cycles the compressor on/off !?!?!?

[iv1777]

so you are saying touching the wires together / un-together definitely cycles the compressor on/off !?!?!?

Yes. Working 100%

[Fe_Will]

Make sure you are wiring the 5V and signal wires correctly. If you send 5V down the signal input on the side car it will overheat the side car board. This can cause the resin on the board to become a liquid and start to flow. It can even become hot enough to desolder the connections. Depending on the duration and extent of damage the side car can sometimes be repaired. Most of the time it is permanent.

[Speeder]

If touching the (2) wire ends that you removed from the pressure switch toggle the compressor on and off it can only be a defective pressure switch. Essentially, that's all the pressure switch is doing, connecting and breaking the circuit at the low and high pressure setting.

[Al Skierkiewicz]

Iv,
Are you sure you are using a pressure switch and not the pressure transducer? The switch should measure shorted (0 ohms) until the pressure reaches about 125-135 psi. The pressure switch has two screw terminals on opposite sides of the device.

It is possible to get the insulation of the wire under the screw terminal on the pressure switch. That would prevent you from giving the proper input to the Crio.