Output's high in Simatic, but not electrical

I deal with a strange problem.
A Customer his machine did nothing all of a sudden.

So, after searching a while, we found that no outputs are high, not a single one. PLC in Run, when I check with monitor in de HWConfig on the output cards, I can see a lot of outputs high, especially when we push on the button lamptest. All 24V on every output group is okay. We placed another output card, made the outputs high, this card works. We did not have spares for the cards used in that machine. We will buy the right spares...

Is it possible that all outputs are blew up ? In the HWConfig, the outputs that are high are not high electrical...
The power supply's of the cards are all connected together and some cables have 230V and 24V together... I'm thinking in the direction of 230V that came on the power supply of the outputcards... The CPU is in Run and says that all cards are in good condition...
In my 10 years carreer I've never seen this.

All input cards are okay...

Suggestions ?

Thanks,
Regards,
Gerry

Sounds as if there is a power problem. Did you check all power connections at the card level? One error often made is to measure the power with reference to a known common level. If the common is not connected to the cards this can lead to faulty signals and/or measurements. The problem can also be related to loose power terminal screws...

Just helping to think about possible solutions.

Kind regards,

hi

Hi,

Thanks for your help.

I measured with the common on the card. 24V measured. Output 6.0 had to be high, I disconnected the wire on that output, led remains off. I also have 2 outputs that give us 2,6V... When I disconnect the connector, 2,6V is off.
I understand that we think that this is a power failure. Strange situation here. It's unpossible that all cards are broke to me... the problem yesterday was that I hadn't spares to replace 1/1.
I also tried to disconnect all connectors and replace 1 by 1. Really annoying problem.

Kind Regards,
Gerry

jvdcande said:

Sounds as if there is a power problem. Did you check all power connections at the card level? One error often made is to measure the power with reference to a known common level. If the common is not connected to the cards this can lead to faulty signals and/or measurements. The problem can also be related to loose power terminal screws...

Just helping to think about possible solutions.

Kind regards,

Click to expand...

I measured with the common on the card. 24V measured.

Click to expand...

Measure the voltage between the earth (PE) and L+, and between PE and M of the cards. What reading does this give you?

The CPU is in Run and says that all cards are in good condition...

Click to expand...

This is not really reliable. I've had problems before where mister Siemens gave me the message "module is available and ok" when the card was broken.

I agree with Jobbe, check the different potentials in the circuit.
Bad grounding can create alot of weird faults.

Results

Hi all,

I measured everything I could, all normal, but no outputs. I connected an extra outputcard and took +24V and M of one of the groups that don't give any output. I made the outputs high and these worked.

We bought new cards, replaced all cards. Outputs okay. Lamptest okay. We added fuses in front of each I/O output-group. We started-up the machine. It's a cascade of many conveyers... all of a sudden all power was down. Circuit breaker of 24V had worked. Fuses all worked... CPU broke + TP177B now. They receive 24V and don't do anything. There has worked a motorprotection too now. We checked that motor with a Megger, it was not okay. We checked the switch(box) in front of the motor, there are helpcontacts in there on 24V + the 3x380Volts of the motor, there was the problem, wires were naked (burned). After fixing this we placed a new CPU and new panel. All okay now.

The problem was that, when that certain motor had to start in the cascade startup, the 24V and motorvoltage made contact, while there wasn't much protection in the closet to protect electronic modules.

We placed a Sitop with fuses for the CPU and TP177B.

We also connected M to PE, this was not done.

The whole installation should be protected a little better now.

Everything runs now.

Thanks guys,

Gerry

This is why you use interface relays on both inputs and outputs

I agree

I agree !!

ojz0r said:

this is why you use interface relays on both inputs and outputs

Click to expand...