Reverse Tunning in Micrologix
- Thread starter Rehu09
- Start date
OkiePC
Lifetime Supporting Member
What model is your Micrologix?
It should support the SCP instruction which can let you take the raw analog values and rescale and invert the slope all in one easy to understand instruction.
For use with a PID, I normally will use multiple SCP instructions. I will scale the raw signals to engineering units first, then SCP the engineering value to numbers scaled for PID in separate instructions. The range for PID values in a Micrologix is normally 0 to 16383 for the process variable, setpoint, and control variable. SO, the setpoint will be entered in engineering units and also scaled for PID with the SCP instruction and the control variable will be scaled from PID units to engineering units before being sent to another SCP block which scales it once again to match the requirements of an analog output card. This might seem like a lot of extra steps, and it is, but it is almost always useful (or necessary) to have the values available in the PLC in engineering units for other logic or for visualization.
It should support the SCP instruction which can let you take the raw analog values and rescale and invert the slope all in one easy to understand instruction.
For use with a PID, I normally will use multiple SCP instructions. I will scale the raw signals to engineering units first, then SCP the engineering value to numbers scaled for PID in separate instructions. The range for PID values in a Micrologix is normally 0 to 16383 for the process variable, setpoint, and control variable. SO, the setpoint will be entered in engineering units and also scaled for PID with the SCP instruction and the control variable will be scaled from PID units to engineering units before being sent to another SCP block which scales it once again to match the requirements of an analog output card. This might seem like a lot of extra steps, and it is, but it is almost always useful (or necessary) to have the values available in the PLC in engineering units for other logic or for visualization.
Last edited:
Thanks for quick response, Im using micrologix 1400
I understood the process of SCP insturction which we do basicallly 4-20ma to 0-16383 and then use the same as processs variable in p&id block. CV of p&id block needs to again scaled to 0-16383 then SCP 0-16383 to 4000 to 20000 basically for the actuator
my question is how can I tune the P&ID block to get reverse tuning
example for 4ma I need to get the valve completely closed 100% closed and for 20ma it needs to open completely which means 0%
Is there any option to change the control mode
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