PLC 2 instruction

Does anyone know what the Scan counter actually does? It is a SCT. I have one in logic with a preset of 0 and accumulated 0. If it actually counted scans I would expect it to accumulate more then 0. I can't find a reset that would be reseting it to 0. There is a contact in the rung which I have not seen high so that may be keeping it from counting scans. I would have expected it to be higher than 0. The instruction may be exactly what it sounds like but I'm looking for conformation from someone that knows. The sct is 647, is 64700 when it is not done and 64715 when it is done? I don't have a manual and can't find anyone that remembers the instruction. Thanks for your help.

Mike

Plenty of vintage forum members will know this but at present they are all lurking in this thread

From the PLC 2 manual:
"This output instruction is similar to a standard counter instruction. During a true rung condition, the Accumulated Value is incremented once per program scan. Unlike counters, however, the scan counter does not count past the preset and resets when the rung goes false, power is lost or the keyswitch is turned to program mode."

So, if your preset is zero......

Link to the manual: http://literature.rockwellautomation.com/idc/groups/literature/documents/pm/1772-pm003_-en-e.pdf

It might be easier to think of it as a TON with a time base of "scans".

Thanks for the response, so if I understand you correctly, it doesn't count past the preset. With a preset of 0 it will go true as soon as the rung is true? The fact that the rung is not true would explain the accumulation at 0. I'm just trying to wrap my brain around what the programmer was trying to do. This logic is for part of the lube logic on a press, we are getting too much lube so I'm trying to figure out what the oem had in mind.

Thanks,
Mike