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2.2.23 Functions StartPID , PID , SetOutPID

Functions StartPID, PID and SetOutPID enables control of a process by

means of PID algorithm (proportional, integral, derivative).

Function StartPID starts the relevant control block and sets parameters as

required. Function can be activated once at the starting or it may be

recalled later to modify quickly control parameters. PID integral action is

initialized only calling this function and setting integral time to 0, otherwise

even in case of switch-off the system will start control action keeping the

same percentage of integral action and consequently limiting the transient

times. Parameters required by function StartPID are the following:

• Proportional band

• Integral time

• Derivative time

• Dead band

Parameters can be entered with numeric format or referring to internal

variables. Integral time is expressed in time unit used for PID function (ex.

PID function recalled every 1 sec., integral time expressed in seconds).

Derivative time is expressed with one decimal digit more than integral time.

Proportional band and dead band are expressed with a numeric value as

setpoint and process.

PID function requires following parameters:

• Setpoint

• Process

• Output value

• Type of control action

• Type of output

After acquisition of necessary parameters values, PID function will enter

the value obtained by control algorithm in the variable “Output value”. This

value will have been obtained rescheduling the percentage value 0 – 10000

(0.00% ÷100.00%) between minimum and maximum value of PID output as

entered using the function RANGE.

For optimal results, PID function should be recalled at regular intervals. A

timer can be used or even an internal Interrupt, to get shorter intervals.

Function SetOutPID is used for control actions which foresee both

automatical and manual functions. The function allows to avoid process

oscillations when changing from manual to automatical PID control.

Following parameters are required:

• Output value

Pixsys PL260 User Manual

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