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R
Hello. I have a PID block in a control logix 5555 that is not functioning. The processor is acting like it is very bogged down, as it changes ladders etc very slowly. We have a PID block that simply will not work. The output is a constant 100% when the block is enabled. The process variable display only line at the bottom of the PID block shows us an input of -327.0000. However, when we highlight the tag for the process variable above in the PID block and monitor it, it shows us that we are at about 290, which is correct. This is a temp application. I have looked at the input, and it is correct. After going thru the scaling process, it shows the 290 degrees just fine. I am baffled as to why I can monitor the actual process variable tag used in the PID and see a value of 290, and yet the PID block will not update it and set the output value accordingly. Be advised that the rung is true, and the enable bit for the PID is set. I have looked at other blocks that are functioning ok, and the value of both process variable display and by monitoring the PV tag are the same. Also, if the rung is not true, I can change the process varialbe display at the bottom of the PID block to whatever I want and that value stays. However, as soon as the rung goes true, the -328.lakd is written in again. Anyone have any ideas? Thanks in advance.
Russ
Russ