1. A Tutorial Overview
Proportional
Integral
Derivative

2. PID Applications Typical Examples Automotive Cruise Control
Temperature Control
Room
Ovens
Glue Applicators
Flow Control
Air Delivery
Liquids
Chemicals
Level Control in Tanks
VFD and Motor Speed Control

3. What does the PID do?
A PID loop Automates what an Operator with a gauge and a control adjustment knob would do.
He would;
Read the gauge to determine the current state of the process
Adjust the knob to bring the process state to the correct condition
Continue to monitor and adjust the knob to maintain the condition

4. PID Terms Common terms used for both methods.
The desired value to where the gauge is adjusted to by the knob is the “Set Point”
Any difference between where the gauges needle is and the desired value is referred to as “Error”
Manipulated Variable or the output level adjusted to drive the process variable to the correct set point.
The position of the needle on the gauge is the “Process Variable”
The amount of time used to collect data from the system is the “Sampling Period”.
The duration of the control output that is turned on and off according to the manipulated variable is the “Control Period”.

5. Typical PID Application
Temperature Control is a common example of how
a controller is used to automatically
Adjust a variable to meet a set temperature point
Hold the variable at that set point
Respond to changes in the set point
Respond to changes in the variable
Respond to changes in the environment
A Control Loop consist of three parts
Measurement by a sensor connected to the process (Thermocouple)
Decisions made in a Computerized controller with set conditions (PLC)
Action through an output device (such as a gas control value)

6. ON/OFF Temperature Control
When the input value is lower than the setting, the output is OFF
If the input value is higher than the setting, the output is ON
Overshoot, Undershoot and Hunting are present

7. MicroSmart PID Control
FC4A has manual PID control
FC5A has New Auto Tuning
FC5A has New Tuning Formula

8. P = Proportional Band To handle the present The Basic Formula is
The error is multiplied by a negative value
Then its added to the controlled quantity (subtracting the error)
The controller output is proportional to the error or a change in measurement (depending on the controller)
Sometimes referred to as the GAIN of the feed back loop
The Basic Formula is
(control output) = (error) X 100 / (proportional gain)

9. Typical Proportional Operation
The outputs Manipulated Variable is in proportion to the deviation between the input value and the setting value in the band
Usually the output is turned on until process temperature reaches Point “A”
Once it is inside the band it will operate quite like the ON/OFF action but is restricted to the band

10. Proportional Gain When proportional Band or Gain is widened
large process swings
Offset from set point is larger
Overshooting
Undershooting
Error grows faster
Unstable, hunting is more pronounced
When proportional band or Gain is Narrowed
The controlled output is turned ON and OFF very close to the set point
Drift away from the set point is easily noticeable
Setting a proportional Gain that minimizes all of the above issues gives the most stable operation.

11. Integral
A simple proportional system oscillates, moving back and forth around the set point
There is nothing to remove the error when it overshoots, it just keeps accumulating
The error shows as a drift up or down of the proportional oscillation
This error is Integrated (added up over time) and then averaged and then subtracted from the Process variable
This corrective action, may best described, as a reset like function
Similar to a person pressing a reset button to a predetermined time cycle

12. What does Integral do ?
The chart below shows an easy to understand representation of the ERROR corrected by the Integral function

13. Integral PI Formula t = Time e = Error d = delta (change in time)
PI or (Proportional + Integral)
Integral action automatically corrects the OFFSET caused in the Proportional action.
The control is performed at, or very near the setting value.
The mathematical formula for the Integral is below
CONTROLLER OUTPUT = (1 / INTEGRAL) [INTEGRAL of e (t) d (t)]
t = Time
e = Error
d = delta (change in time)

14. Limitations of PI Control
It may take some time for the controlled output to stabilize if there is a disturbance in the process variable or the set point
If the integral action time is to shortened, correction becomes strong and the OFFSET is corrected for in a shorter time but hunting is likely to occur
If Integral action time is to long, correction becomes weaker, and it will take more time to correct for the OFFSET
PI correction is best suited for control, in which
slow change is required

15. PID TUNING Manual Tuning, operator performed & calculated
Closed versus Open Loop Tuning
Controller tuning techniques are classified as closed or open. Closed loops are more often used and typically give the advantage of giving more realistic results, because the process and controller operate together normally. Open loops are very seldom used for other then Batch process systems.
Auto Tuning or a shelf tuning calculation
Samples are taken by the control device for a short period just after start-up, which are then processed through a tuning formula and applied to the process

16. THE IDEAL PID TUNING
When the PID is tuned properly the result should look like this
As the process variable settles in around the Set point, it should oscillate as shown
Each subsequent hump in the oscillation should be ¼ the size of the previous one

17. MANUAL PID TUNING
The Ziegler-Nichols Closed-Loop Method: This manual tuning method is used for best results
Remove both the reset (Integral) and error reduction (derivative) actions. Set the controller to PID and place the set point at the most often used level.
Generate an upset in the loop and adjust the gain (proportional) until the loop cycles with a constant amplitude to both sides of the set point. Typically gain settings are between 60 to 80% of process.
Use of a chart recorder may be helpful.
An upset in the process can be produced by increasing or decreasing the set point by some arbitrary amount (about 10 to 20%), waiting until the process begins to respond, then returning the set point to its previous value.
Record this Proportional value as Ku

18. MANUAL PID TUNING Record the period of the oscillations (Pu)
Determine the settings from the equations on the next slide
Program the settings into the controller thru the WindLDR
software.

19. MANUAL TUNING FORMULA
Basic Tuning equations for calculating PID settings using the Ziegler-Nichols Closed-Loop method
Proportional is 0.6 Ku
Integral is 0.5 Pu
Derivative is Pu / 8

20. The PID Function Block The PID Operands S1 = Control Register
S2 = Control Relay
S3 = Process Set point
S4 = Process variable (actual state of the process)
D1 = Manipulated variable ( PID correction output)

21. The PID Function block
Double Clicking on the PID Function Block brings up the Set up Dialog Box tool.
Fill in the boxes with valid Operands.
For help please use the guide lines listed in Chapter 21 of the Users Manual.

22. The PID Function block The Module type
for the End refresh type of Analog Card
for the ladder refresh type of Analog Card
The Data type
Select Word (W) or Integer (I) when using the Ladder refresh analog module type.

23. The PIDST Function Block Macro
This Dialog Box MACRO makes it easy to set the Operands for the PID Function Control Block.
Set the Module type
Set the Data Type
Set the first three Operands (S1, S2 and S3) for the PID Control Function Block that this MACRO will set up the parameters for.
This ties the two Function Blocks together.

24. For our example it should look like this

25. Set the PID Parameters Operation Mode Control Action Integral Action
Proportional type

26. PID Action Operation Mode Parameters Set By PID Action User
Auto tuning and PID Action User
Auto Tuning User
Advanced Auto Tuning and PID Action Fully Automatic
Advanced Auto Tuning Semi Automatic

27. Control Action When tuning Manually the Control action must be chosen.
Direct Control Action
Reverse control Action
When Auto Tuning is chosen then this is set for you when it auto Tunes.

28. Direct Control Action
Is used for cooling temperature control

29. Reverse Control Action
Is used for Heating temperature control

30. Integral Action
Disable sets the Integral to start at the beginning of the PID action
Enable sets the Integral to start when the process variable gets to a percentage of the proportional term.

31. Proportional Action Proportional Term
Gain: The Output Manipulated Variable is calculated from the deviation between the Set Point and the Process variable.
Band: The Output Manipulated Variable is calculated the same way but the Integral action is only on while the process variable is between the set Point and the limit set by the Band.

32. PID Action Parameters Set Point This must be set by the operator
This is the point in the process that you wish the process variable to operate at.
The Set point may be changed at any time by entering a new value into S3 of the PID Control Function Block

33. PID Action Parameters Sampling Period
The sampling period determines a time interval between PID executions
PID executions are in relation to the beginning of each PLC SCAN.
The sampling period may be longer then one SCAN time.

34. PID Action Parameters Control period
The Control Period is the duration of the ON/OFF cycle of the control output.
The ON pulse duration is set by the combined product of the control period (S1+13) and the output manipulated variable (S1+1).
PID Control Operand is (Control relay S2+6).

35. PID Action Parameters Proportional Gain
This sets the amplitude of the swing of the process variable above and below the set point.
Only used during the manual setting of the PID
A good starting point would be 60%
For maximum performance Gain must be set using a trend chart recorder.

36. PID Action Parameters Integral time
This must be set by the operator during manual PID tuning.
This is the time interval in the process that you wish the Integral reset action to operate at.

37. PID Action Parameters Derivative Time
This must be set by the operator during manual PID tuning.
This is the time interval in the control period that you wish the derivative ERROR to be removed from the process.
Derivative Gain
This is a value usually set between 20 to 30 % to help eliminate noise or fluctuations in the process variable.

38. Input settings Linear conversion Disabled
The process variable is stored in the PID Function without Scaling or conversion
Enabled
When enabled the conversion function is useful for scaling the process variable to an actual engineering value.

39. Input settings Input Filter
Used to smooth out fluctuations in the process variable.
Helps stabilize the reading of the process variable, such as temperature readings when the value changes faster then the sampling rate.
In effect during Auto Tuning and PID action.

40. Input settings High Alarm
When the process variable is higher then or equal to the set value then the S2+4 control relay will activate
Low Alarm
When the process variable is lower then or equal to the set value then the S2+5 control relay will activate
These settings have nothing to do with Auto Tuning or the PID action and must be set independently

41. AT Parameters The AT parameters tool box is used for Manually setting
The Set point is the point at which the Auto Tuning stops and the PID action starts
Usually set to the same value used for the process set point.
The sampling period sets the rate at which data is collected from the process during Auto Tuning only.
The control period sets the ON/OFF cycle of the control output (S2+6)
The AT parameters tool box
is used for Manually setting
the Auto Tuning by user
The output manipulated variable
Limits the amount of output during
Auto Tuning only

42. Output settings This is not used for analog output values from the PID
PID Control Function Block destination operand (D1)
The manipulated variable is displayed as a range from
0 -100
Disabled
The range is set to 0 – 100
Enabled
The range can be limited to upper and lower limits.
Such as 26 and 49
This is not used for analog output values from the PID
Use Data register represented by
S1+24