Help! My system seems to have developed a current leak!

[Mischief55]

I don't actually think my analog input module is the problem but here are the details:
I have an Aromat FP10 analog module 24vDC with 4-20 mA inputs. I read several position transducers and 3 pressure transducers. On Friday, they all flat-lined at their present readings for about 4 hours. After that they all seemed to have an increase of about 7%. Shut the system down and all seemed fine until today when they slowly started increasing back up to that 7-10%. I've checked most of the circuit but haven't found anything yet. Has anyone else ever experienced this and what did you find? This is the only system I've ever worked on so I'm really scratching my head. Any advice would be most appreciated.
Thanks,
Sarah

 

[L D[AR2P#0.0]]

Did you measure the current with a meter ?

 

[Mischief55]

checking current

My partner and I are doing that right now. Will get back to you with results.

 

[Mischief55]

These are the readings from the peripherals without being connected to the PLC:
Input 1: 5.7 mA
Input 2: 0 mA (definately a problem)
Input 3: 3.68 mA (don't know why this is below 4)
Input 4: 6.05 mA
Input 5: 6.06 mA
Input 6: 6.05 mA
Input 7: 3.05 mA
Input 8: 3.73 mA

All are on the same 24 vDC current loop. Can some of the peripherals be dragging the numbers down on the others? Thanks for your help.
Sarah

 

[Lancie1]

All are on the same 24 vDC current loop. Can some of the peripherals be dragging the numbers down on the others?

Sarah,

Do you mean that all thess inputs have the same 24 VDC power supply? Yes, if there is a short-circuit to ground (check the wiring for Input 2, maybe disconnect Input 2 from the Panasonic FP10 module) then that could pull the power supply voltage low and make the currents read high.

Another reason might be that the Panasonic Aromat FP10 analog module is failing (going bad slowly).

 

[Lancie1]

Sarah,

I can not find any details about a Panasonic Aromat FP10 Analog Input Module.

I do find information about the Panasonic Aromat FP-X Add-on Analog Input Cassette, Part number AFPX-AD2. Apparently each cassette has 2 analog inputs. Do you have an older version of the Aromat PLC?

http://pewa.panasonic.com/automation-controls/plc/fpx/expansion-units/

 

[Mischief55]

Hi,
Thanks for the help. We found a loose wire on Input 2. Its got 6.5 mA on it. The three low voltages all come from a long run. We're going to chase that tomorrow. Just in case I found some spare units on Ebay and ordered them. Again thanks for your help.
Sarah

 

[Lancie1]

Great! Success causes good feelings all around!

 

[Mischief55]

Yes, the FP10 is an older model. This was installed in 1999. The modules are also for the FP3. Not complete success yet but closer. This long run has at least 6 junction boxes over a quarter mile run in some challenging terrain, this is going to be a fun day! Thanks once again for all your help.
Sarah

 

[Lancie1]

This long run has at least 6 junction boxes over a quarter mile run in some challenging terrain,

Hmmm...I would check those 6 boxes for problems such as water damage from leaking gaskets, and insect and rodent nests. Wasps, bees, snakes, and mice love unattended junction boxes! Carry gloves and insect spray.