The PID Control Loop Function is designed for practical process applications. The
complete design incorporates the linking of tags on the
WinCC
mimic,
with the display of the PID control and monitoring variables.
It also includes a pop-up template, with detailed display of
the analog input, setpoint,
and analog output.
The Step7 function is easily
incorporated into an existing or new PLC project. With the use of the Step7
function and the WinCC
mimic, template,
and structured tag that is supplied, implementation and tuning of a PID Control
Loop no longer has to be a daunting task.
MIMICS :
Mimic Display : Analog Input values are displayed on-screen using the
available Analog Input Function. The controlled device, e.g. Flow Control,
VSD, Temperature Control is linked to the template via a tag on the mimic.
Alarms and warnings are linked to the Analog Input, not the PID.
TEMPLATES :
Further information of PID values and parameters will be made available when the operator
clicks on the tag of the controlled device, thereby opening
the PID template
(example) as shown below :
1. PID control can be switched ON / OFF by the operator, or can be overriden in
the software
2. Status indication shows whether PID is switched on by operator or PLC, and
shows status ON or OFF
3. Scaling of Setpoint and Process Variable is displayed here e.g. 0-100
4. Graphic representation of SV = Setpoint Value as scaled to its full-scale
value
5. Graphic representation of PV = Process Value as scaled to its full-scale
value
6. Graphic representation of Output Value as scaled to its full-scale value
7. Numeric value of SV = Setpoint Value. Can be modified by operator with
correct access level
8. Numeric value of PV = Process Value. Engineering units can be displayed
9. Numeric value of Output Value
10. PID Control can be overridden with a fixed Output Value. Forced Output Value to be used if "OP" is on
11. Toggle "OP / CONT" to switch control of output value between
operator and PID
12. "P", "I", "D" for Proportional, Integral, Derivative are shown in these
fields. Can be edited (access level protected)
13. In the PLC DB extra lines of information can be entered for each PID
14. A tag name can be assigned to the PID and displayed
Use the ActiveX control below to find out more about the features of this
module :
FEATURES :
VISUAL :
- Graphical and numeric representation of measured value, setpoint, and
output value
- Visual confirmation of tag name on display
- Displays whether control is on/off or forced on
- Operators can modify setpoints (access level protected)
- Technical staff can modify PID parameters for loop tuning (higher access
level protected)
- PID can be forced to a fixed output in case measurement fails or PID
becomes unstable
PLC :
- PV (Process Value) and min-max scaling is read directly from Analog
Input Function
- P,I,D values can be edited
- PID Function can be interlocked to stop under certain conditions
- On/Off control can be done via PLC code, or operator control from
template
- Ability to "reset" PID for a clean restart each time
- P,I,D Set values are fed to display on template direct from datablocks
- Additional devices e.g. pumps, valves can be switched on/off when
activating the PID
- Addressing of output is done directly to controlled variable e.g. QW224
WHAT IS INCLUDED :
The PID Control package includes the following :
WinCC :
Full step-by-step configuration and instruction manual.
Example mimic with PID Control implementation
Usable Mimic display items. (copy/paste from example)
Structure tags in WinCC
Pop-up template (as WinCC .pdl files)
Step7 :
Full step-by-step instruction manual.
Example function and datablock with PID Control implementation
Structured tag (UDT) for creating new datablocks
PID Control Function (FC) for use in programming.
