J
Just curious if anyone has experienced a PID block in a SLC 5/05 freezing. The scenario that this happened to me was when I "calculated" a process variable (basically an average of all sensors) and when the PID was not required (placed in manual) I would clear this temporary calculation. Before putting it back in auto, all in one scan a new average would be calculated, the block placed in auto, and then finally the PID block was scanned at the bottom of the ladder. For the first 5-7 minutes, the PID output would freeze at zero (0%) even as the scaled error continued to grow. After this delay the PID block would work fine as it is expected to. After much headache I discovered that if I didn't clear this temporary average when the PID block was offline the PID block would respond right away no problem. Basically what I have summized is that AB PID blocks do not like a huge change in scaled error that can be attributed to either a drastic/instant change in PV or possible setpoint as well. Even though I put the block in and out of auto using the bit in the control word this still occured. I understood that if it was in manual it shouldn't matter what you do. Anyway any thoughts or insight into this? Anyone else experienced this?
Thanks,
J
Thanks,
J