RSLogix 500 Question

Hey guys, quick question.

I'm trying to figure out how an old piece of equipment works in our plant so I can make some slight modifications.

Basically, all it does is dispense fluid (transmission fluid) into our product when the operator squeezes the handle.

I believe that it turns on a solenoid which will allow the fluid to flow if the handle is squeezed...as the fluid flows, it counts pulses from a flowmeter...then when the setpoint is reached, it shuts off the solenoid so that no more fluid can be dispensed (even if the operator keeps holding the handle down).

My question is this...I believe they are using the Event Input Interrupt to accomplish this. I have never dealt with this instruction before. In the subroutine that the EII points to is a counter on a rung by itself, no other conditional logic. The "input select" that the EII uses is the input pulse from the flowmeter.

So am I correct in thinking that every time the flow meter pulses, the program scans that ladder and increments the counter by 1? I see no "JSR" to scan this subroutine, so I assume that it ONLY gets scanned when the input goes high from the flowmeter...?

Just wanting to make sure I understand how a EII works! Thanks for any help ahead of time!

Forgot to mention, this is a Micrologix 1100 PLC that I'm referring to!

Your assessment of how the Event Interrupt works is correct.

The EII is configured to execute a specific Program File number when a specific input is triggered. It can use the fast input hardware of the MicroLogix, so it's great for catching short pulses and reacting to them faster than the ordinary program scan could.

It's not perfect for counting fast pulses; the High-Speed Counter feature, which uses the same set of input hardware as the EII can, might be more appropriate because it's dedicated to counting right down in the hardware, rather than relying on a PLC logic file.

But in your case, the pulses might be slow enough that the simple EII with a Counter in it is enough to catch them all.