ML1500 Output Stage Problem

Hello to the community.

I am facing a weird problem with an output on a ML1500.
An output (O:0/3) that control the main motor of doser should be ON until the sensor that position the doser on a "X" position goes ON, then after a few milsecs (310) that output (O:0/3) goes ON again.(infinity Cicle).

The problem is that after while sometimes a few minutes, the output on the PLC status stay ON but there is no voltage crossing through the relay (Outputs Relays), so the doser doesn't move and stop the process. I have to stop for couple minutes and then start again in order to make the output work again

I know is not a programming issue. (more than 4 year with that program)
I'm think it could be a issue with "VAC/VDC".
Note: I do not have power lose or fase lose

Please Help

gmondrax said:

Hello to the community.

I am facing a weird problem with an output on a ML1500.
An output (O:0/3) that control the main motor of doser should be ON until the sensor that position the doser on a "X" position goes ON, then after a few milsecs (310) that output (O:0/3) goes ON again.(infinity Cicle).

The problem is that after while sometimes a few minutes, the output on the PLC status stay ON but there is no voltage crossing through the relay (Outputs Relays), so the doser doesn't move and stop the process. I have to stop for couple minutes and then start again in order to make the output work again

I know is not a programming issue. (more than 4 year with that program)
I'm think it could be a issue with "VAC/VDC".
Note: I do not have power lose or fase lose

Please Help

Click to expand...

If a relay output has been operating continuously for over 4 years then it has most probably reached the end of its operating lifetime. You didn't say how frequently the relay output is driven off, but even if it is once per hour, it will have done 35000 cycles (assuming the machine ran continuously). That is a lot for a relay switching even a light load. From your description, I would guess that the relay contacts are worn-out, or burnt-out, and not making good contact when the relay is energised. Also, is there any suppression on the output driving the motor ?

Is there an unused output you could change to ? That might buy you time to consider future options.

If not, you will most likely have to replace the base unit 1764-24BWA, or you could consider adding a Compact I/O expansion output module, giving you solid-state outputs, such as the 1762-OA8 (AC 120/240V), or the 1762-OB8 (DC 24V).

You will, of course, have to change the program to address the new output if you change to an existing unused one, or you add an expansion output module.

More information on what the output is driving will be required to inform better.

Thanks daba. We changed the base unit of ML1500 and everything is working again now.