Time Based Interrupt

[Bryll 31]

PLC: FX3U Software: GX IEC Developer 7.04 Tried to create a function that creates a short pulse with a fixed pause to open a relief valve when the system pressure reaches a certain level. This to prevent the systems safety valve to open. When doing this in the code was the active time of the pulse not constant. So, I made an interrupt routine (time based) and increments a counter value for pulse output high length, and the same for pulse output low length. When simulating overpressure by the analog pressure register is the function activated. But, the funny thing is that you can hear the variation of the pulse length, thought that the interrupt would cure the variations of the pulse length, but no. Any suggestions ?

[Inntele 60]

Hi Bryll, What number of discreate output do you use (Y0 or Y1 or... Y30)?

[Bryll 31]

Hello Inntele, You got me there Your question made me aware of the fact that the output used is on a distributed I/O unit with Modbus TCP/IP communication. Not strange at all that I get a pulse variation. I have to rewire the output to Y0 - Y7. Thanks a lot

[Inntele 60]

Hi again, Good! Also I'd like to remind you about the existing of REF instruction [FNC 50] to refresh local outputs, that does not support high-speed operations

[Bryll 31]

Hello again, Yes, I will rewire the outputs to the PLC outputs, and of course also use the REF instruction. Didn't think of the delay caused by the Modbus communication until you asked about the outputs. Guess the brain stalled due to other issues (HW) we had at the same time. We actually trashed a flow sensor, a compressor and a dew point sensor. All silly expensive EEX classed items Thanks again for your help

[Inntele 60]

Don't mention it !