help OSR with micrologix 1100

So I have micrologix 1100 program that controls sonic welding system. The ladder logic currently sents output to welder to allow cycle to start after certain inputs are met. One of those inputs is a part present input. This input is an laser switch that detects part on the welding fixture. The operators have taped this sensor in such a way that welder will run without a part in fixture.... which can cause some damage. I need to make a condition that the part was actually removed from the fixture. sensor must go low then high before next welder cycle. can I use the OSR instruction? any help?? thanks

Hello and welcome!

You might need a OSR (One-Shot) instruction, but it seems that Timer (TON or RTO) would be more appropriate. Add logic where a "Machine Running" bit being ON AND the "Part Present" Input going False (or OFF or open) both starts the new timer. Set the Timer Preset Time Value to however long you want to see this switch off (probably 2 or more seconds, depending on the normal gap between parts). If the timer ever reaches its time setting (Timer enables its DONE bit), you know that the switch is taped up, so you display a warning or error and disable the machine, or whatever other action is appropriate.

To make sure that your machine only makes good parts you could also add logic so it detectes when the part was loaded on the fixture and then removed before it was actually welded.
We call it a part load fault.

The other thing you could do is measure duration of the weld and compare to preset. If measured time is shorter than preset then fault.

Tom

The other half of this is "WHY" they are taping off the laser? If we can assume for a moment that randomly taping off sensors for the pure joy of it then it is likely that

a) The sensor has not been working properly or is causing nuisance faults.
b) Taping off the sensor provides them with a significant cycle time speed advantage.
c) There is some reason that faking a part present every now and then provides some sort of maintenance function.

Simply preventing them from taping off the sensor without addressing WHY they are doing it may solve the damage issue, but may also result in a more frustrated and unhappy operator or a slower less effiecient machine.

I agree with Damian, it sounds as if you have a timer in the cct to confirm the lases is hit correctly (debounce) check this setting - it may be set to 1 second - hance the operator is taping it out.
as has been sugested simply make sure it is off before the cycle can start.
(an Anti-repeat cct) will prevent the operator from taping it.
be wary of bits of string after that.
(first hand experiance - took 3 months to find though.

thanks all, for your responses. doing some investigation on why its happening, then put some of your ideas to work. I like the part load fault logic, no experience with doing that type of detection logic, but will make an effort. thanks again!