Modicon Trouble

[dussery]

Hi everyone,
I have a quantum plc with modicon i/o drops. I am a running modbus plus network. Right now I have several problems.

1. One of my 140 DDI 353 input modules has a constant 20 volts on all terminals.

2. Two of my control panels, from Automation Displays Inc., have no indicator lights. The switches open and close doors but the indicator lights do not work.

Any suggestions??

Thanks
Dussery

 

[Jim Dungar]

What troubleshooting steps have you performed?

for example, you say you have a constant 20V on all of the terminals of your input module. how are you measuring this? What terminal are you using as a reference? What voltages do you read on other input modules?

 

[dussery]

Modicon troubleshoting

I am using the chasis ground as a reference.
All of the terminals have 20 vdc.
On a known good terminal there is 0 volts when the point is off and 20- 24 volts when the terminal is on.
I have swapped the remote I/O module and the problem persists.
I have changed the DDI 353 module and the problem persists.

Thanks,

Dussery

 

[Jim Dungar]

The DDI is an input card, if you have voltage on the inputs could it be coming from your field devices/power supply?

 

[Bstubby1]

I have run into problems with input cards if the "common" is not connected properly. Have you checked that?

 

[dussery]

I have checked voltages and wires several times. Today my system lost partial communications. I had some doors that would open and close normally and other doors in the same area that would not respond. I have a Modicon 140 NOM 211 00 " Network Option Module" that seemed to lose communications. The Modbus + LED did not blink at 6 times per second. I disconnected the Modbus tap and reconnected the wire. This seemed to work and the NOM started working normally and all of the doors started working properly. Is there something that might cause a system to lose partial communications

 

[Jim Dungar]

Among other problems these could cause intermittement/incomplete communications.

not following manufacturer bonding (grounding)requirements - these problems usually take a few years to become apparent.

not installing MB+ connectors correctly especially in high virabtion areas.

having a comms device on the network that is in a questionable operation condition

 

[dussery]

Recently I had two panels with no operating LEDs. All other controls worked properly. Just no LEDs to indicate open doors. Suddenly all of the lights blinked and all of the LEDs started working properly. The LEDs worked for a day. As I was troubleshooting a totally unrelated circuit the panel lights went out again. This was puzzling because the circuits used different I/O modules and had nothing in common other than the CPU and Modbus Plus network.

Baffled again,
Dussery

 

[Sliver]

I would try to monitor your power quality to see if it is stable.
Do you have a large load on the same feed that could be drawing down the voltage?

 

[dussery]

Power is sourced from more than 20 supplies. i would not be so confused if nothing worked. But it is hard to place when all the doors work buth the LEDs do not work. The I/O modules wore swapped for know good and the proble still persists. Is it possible for a system to have partial communications on a Modbus Plus network.

 

[Jim Dungar]

I am not sure what you mean by "partial communications".

Modbus Plus does not have any firewalls or filtering. These functions are handled by the communicating devices themselves, MB+ is just a medium for standard MODBUS commands. It is possible to have two devices with the same MB+ address. Duplicate addressing would result in unpredicable communications.

 

[PeterW]

Power sourced from more than 20 supplies????

That sounds ominous.

(Back feeds anyone)

 

[dussery]

opps, let me clarify. I have one power supply for my plc and Quantum I/O units. I have additional supplies for the momentum I/Os, input, and output devices.