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I’m looking for an example or a function block that enables automatic switching between manual and automatic mode without any interference from the PID control. I’ve tried to create such something on my own, but the results weren’t good
As a supplementary note, I used a FB41 module to do this
The background data block is used as a digital switch, with the two buttons on the screen set to 1 and 0 respectively to enable manual/automatic switching. By default, when switching to automatic mode without using any auxiliary programs, the value starts increasing from 0. What I want is for it to start adjusting around the current manual output value, just like in DCS
FB41 already allows for a seamless switch from manual to automatic mode; all you need to do is switch from automatic to manual mode. Define a variable for the MAN_VAL pin named abc; when set to automatic, the output move from FB41 can be assigned to abc.
OP, seamless switching means that when switching manually to automatic mode, the SP value equals the current PV value; with this value being passed along, it constitutes seamless switching.
For PID control, it is generally done manually first, adjusting the value until the desired PV level is reached, after which it is switched to automatic mode. During manual adjustment, as long as the SP value tracks the PV value, a smooth transition can be achieved when switching to automatic mode
In actual use, no matter what manual setting has been set, when switching to automatic mode, the adjustment starts from zero and increases gradually. For example, if my valve has already been manually adjusted to 50%, which is close to the value required by the process, switching to automatic mode doesn’t allow adjustment starting from 50% like in a DCS system; instead, it starts from 0%. What I’m asking is how to achieve adjustment starting from 50%, just like in a DCS system
It’s better to ask these questions on the Siemens technical forum; there are few people here who are experts in PLCs
It’s better to ask these questions on the Siemens technical forum; there are few people here who are experts in PLCs