S5 issues

I have a string encoder that gives a signal to a interface board then that gives a signal to my S5 counter card (not sure of the correct terminology)

The values in the plc are showing the correct value, (example) I tell the program to move to position 19000, it will go to 19002...perfect (close enough) but its more then a 25mm off, sometimes 50.

I have tried to trouble shoot it the correct way, also I have done the part-swap thing, check all teminations, Bla, Bla...still not getting far...the bad part is, its not all the time, so now im thinking noise? maybe?

Parts that I’m using
Siemens S5 115 U
Siemens counter? card 6ES5 242-1AA32
Manufacture unknown, it has some Siemens parts RS 422? (I think this is some kind of signal converter)
ASM encoder string encoder

Here’s the real bad part, all that I have and can find is in German, the encoder is obsolete, can’t find much on the Siemens card, I have tried changing all parts, same results…So I’m going for the noise thing, I have 15 SEW Euro drives on this machine as well.

Any suggestions?

Regards,

Mark,
Check if it happens when some of drives is in generator mode (negative energy, hoist going down for example

marinko,

Thanks for the reply, thats what I have been trying to look at today, I changed the PLC program so that all other drives are stoped when the hoist moves...still watching

Is it posible that if the hoist is not 'enabled' but one of the other drives is running that the noise from the running/enabled drive change the value on the hoist?? , just a thought...

damn its a lot easier when it breaks..

I thought I said I hate these problems

It it is noise then the position should move even when not commanded. Tell the motor to go to 19000 and mark the location. A dial indicator would be nice. Now turn on the possible sources of noise one at a time and notice if the motor 'drifts'. The noise will add or subtract counts but the PID will always try to keep the counts at 19000 so the motor will move in response to the noise.

If the motor moves without any noise generating equipment turned on then disconnect the encoder and type the phases to separate resistor. There shouldn't be any noise. If there is then disconnect the wires from the encoder to count converter and short out its inputs. At some point you can divide the problem in to smaller problems.



You need a scope to measure the voltage levels of the encoder. I doubt the system is using differential line drivers like what you would see on a modern system. If the encoder uses differential line drivers you will see an A+ A- B+ B- Z+ Z-. If not then your encoder is not using differential line drivers and the system will be MUCH more susceptible to noise. At this point you need to check the commons and grounds.