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ContentPulse Width Modulation (PMW)PID ControflerCtosed Loop Controlled SystemController BufidAdd Cyclic Interrupt OBAdd PID ControllerCompact and Expanded ViewFormal Parameter - InputFormal parameter- OutputFormal Parameter - SlateDefine VariableConfigurationInput ScalingInput MonitoringSet PWM HysteresisOutput LimitsManual PID parameterVariable for Warning LimitsCommissioning - WorkflowCommissioningCommissioning - Kind of CommissioningCommissioning - OnlinePID Exercise ....................................................................................................................................Exercise - PID ControllerExercise 8-1: Add Ne~v Project with HardwareExercise 8-1: Setup PLC tagsExercise 8-1: Add program and OBExercise 8-1: Add P]D ControllerExercise 8-1: Parametefize PID ControllerExercise 8-1: Scale the InputsExercise 8-1: Download whole projectExercise 8-1: Commissioning PID Controfler

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SITRAIN Training for $7-1200 TIA SystemAutomation and Industrial Solutions Page 1 Pulse Width Modulation & PID Controller

PID Controller

Exercise PID

SITRAIN Training for $7-1200 TIA SystemAutomation and Industrial Solutions Page 2 Pulse Width Modulation & PID Controller

Pulse Width Modulation (PWM)

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CTRL_PWM InstructionThe CTRL_PWM Pulse Width Modulation (PWM) instruction provides a fixed cycle time output with avariable duty cycle. The PWM output runs continuously after being started at the specified frequency(cycle time). The pulse width is varied as required to effect the desired control. Duty cycle can beexpressed as a percentage of the cycle time (0 - 100%), as thousandths (0 - 1000), as ten thousandths(0 - 10000), or as $7 analog format. The pulse width can vary from 0 (no pulse, always off) to full scale

(no pulse, always on).Since the PWM output can be varied from 0 to full scale, it provides a digital output that in many ways isthe same as an analog output. For example, the PWM output can be used to control the speed of a motorfrom stop to full speed, or it can be used to control position of a valve from closed to fully opened.

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Pulse Width Modulation (PWM)

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Two pulse generators are available for controlling high-speed pulse output functions: PWM and Pulsetrain output (PTO). PTO is used by the motion contro~ instructions. You can assign each pulse generatorto either PWM or PTO, but not both at the same time.The two pulse generators are mapped to specific digital outputs as shown in the above table. You canuse onboard CPU outputs, oryou can use the optional signal board outputs. The output point numbersare shown in the above table (assuming the default output configuration). If you have changed the outputpoint numbering, then the output point numbers will be those you assigned. Regardless, PTOI/PWM1uses the first two digital outputs, and PTO2/PWM2 uses the next two digital outputs, either on the CPU oron the attached signal board. Note that PWM requires only one output, while PTO can optionally use twooutputs per channel. If an output is not required for a pulse function, it is available for other uses.

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Page 4 Pulse W~dth Modulation & PID Controller

PID Controller

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, Pulse Width Modulation (PWM)

¯ PID Controller

, Exercise PID

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Closed Loop Controlled System

Controller

w e

actuator

Controller PWM

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Controlled(disturbanCe)

z

Fan

High Speed Counter

A block diagram showing a PID closed loop control implementation where the measured feedback iscompared with the setpoint to determine the error. The error is then used by the PID loop algorithm to

adjust the PID output to eliminate the error.

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Closed Loop Controlled System

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actuator(disturbance)

Z

Controlled

Controller PWM Fan

High Speed Counter

The PID controller is implemented in the 1200 CPU by the PID Compact instruction box located in theExtended Instruction Task Card. This PID control loop will use-a PWM instruction and a High SpeedCounter instruction to control the speed of the fan motor on the training simulator.

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Controller Build

PID Loop ControllerThe PID Compact instruction provides the CPU 1200 user with a PID loop control algorithm that hasautomati’~ and manual mode available along with self tuning optimization ¯ The pID_Compact instructionbox has inputs where the setpoint and process variable (actual value) are connected. The inputconnections provide process data for the PID algorithm which then drives the output to the final element.

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Controller Build

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The PiD Compact instruction is programmed in a Cyclic Interrupt OB for execution which executes at aspecifie~-cycle time. The cycle time can be viewed or changed in the prope[ties of the Cyclic InterruptOB. During the programming of the PID_Compact instruction a data block is created and automaticallyplaced in the Technological Object folder.

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SITRAIN Training for Page 9 Pulse Width Modulation & PID ControllerAutomation and Industrial Solutions

Add Cyclic Interrupt OB

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Adding and configuring the Cyclic Interrupt OB through the Add new block prompt in the Program blocksfolder. When the Add new block dialog box opens, the OB button is selected followed by selecting theCyclic interrupt, the program language, the OB number, and cyclic execution time; click OK to complete

the configuration.

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Add PID Controller

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Open the Cyclic Interrupt OB to view the LAD networks, then open the Extended Instructions and dragand drop the PID Compact instruction on to the open LAD network. A dialog box will open where aninstance data bloc-k will be configured and be attached to the pID_Compact instruction box.

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Compact and Expanded View

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PID Compact instruction box can be expanded or collapsed by clicking on the little arrow head at thebottom of the PID_Compact instruction box. tn the expanded state, additional inputs/outputs are exposedand connections can be made then the instruction box can be collapsed to conserve space.

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input:"Automatic Mode"

.= from the user programAnalog Input

:= "Manual mode"

~dable for °Manuat Mode"restart counter

:= "inactive Mode"

The PID Compact instruction inputs not only provide connection points for the controlled processsetpoint-~nd measured feedback, it also provides an input connection to change the state of the

controller mode. 1he PID controller can be in manual mode, which is the default mode, or auto mode.When the PID controller is in auto mode, the P[D controller automatically adjusts the loop output tomaintains the loop’s setpoint value, such as a desired temperature.

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The PID Compact instruction outputs not only provides a connection point for the controlled process finalelement-~ut it also provides different types of output connections to match what it is driving, such as anoutput for pWM or an output as a Real number data type. Limit and warning alarm bits can beconfigured along with locations that record the mode of the controller and displays error codes in theevent of an error condition which makes troubleshooting easier.

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Formal Parameter - State

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The chart above shows the numerical codes that are displayed in the State output which describes theStatus of the PID controller. A memory location must be configured to State output in order for the

numerical codes to be displayed.

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Define Variable

Symbolic programming provides an advantage, you will find the program much clearer and easier to readif you use symbols (for example fan) instead of the absolute addresses. To allow the use of symbols, youcan enter a name, the absolute address, the data type and a comment for every address used. Onceyou have defined a symbol, it can be used throughout the entire user program of a programmablemodule; symbolic names are entered in the PLC tags folder.

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Clicking on the Configuration button in the upper right hand corner of the pID_Compact instruction boxopens to the configuration topics such as Basic parameters, Input scaling, and Advanced settings whichstores the loop tuning parameters for the pID_Compact box instruction.

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Input Scaling

Configuring the Input/Output fields in the dialog box is made easier by the following special features,

The Intellisence feature aids in configuration by providing a list ofIntellisense and automatic connection, slideonly valid possible connection variables (symbolic names) like the Input value input shown in theabove. The automatically connection feature then connects that symbolic variable to the correct input oroutput of the pID_Compact box instruction.

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Input Scaling

The input scaling takes the raw data value from the analog input signal such as 0 to 27648 or -27648 to+27648 and assigns the desired engineering units. So that the value entered at the upper limit is now

associated with the max raw data value of 27648 and the value entered at the lower limit is nowassociated with the minimum raw data value of 0 or -27648. This is dependent on the type of analogsignal entering the analog card.

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Input Monitoring

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Numerical alarm warning points are entered into the input monitoring menu prompt and will be used toset alarm bits that can be configured on the pID_Compact instruction box.

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Set PWM Hysteresis

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Edit the PWM limits menu prompt to enter the minimum on time and the minimum off time of the outputsignal of the piD_Compact instruction. PID_Compact instruction will not change the signal Time-on orthe signal Time-off past these limits.

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Edit the Output limit menu prompt to enter an upper limit and a low limit for the PID_Compact instruction

to use in the function calculation.

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If the PID tuning parameters are known, the PID tuning parameters values can be set manually throughthis configuration dialog box and then the check box should be checked in order to utilize thoseparameters, as shown in the slide. The PID tuning parameters can be determined by using the auto-tune

feature.

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Optional warning alarm bit variable can be configured in the piD_Compact instruction box to provideinputs to logic operation and/or drive animation on the HML

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Commissioning - Workflow

¯Download Projected controller +technological object

¯ start commissioning

¯start scope

, Run "Startup Tuning"(turn-over tangent method)

¯ Run "Tuning in Run"(Step response)

¯ Upload PiD-parameterto project

¯ activate automatic modeSet [oPID_compact-DB°’sRet’i-M°de] to mode 3

After the PID Compact instruction box has been configured and compiled, the program can be downloadto the 1200 C-PU then tested through the Commissioning function as listed in the slide.

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SlTRAIN Training for Page 25 Pulse Width ModuLation & PID ControllerAutomation and Indus~a! Solutions

Invoke the Commissioning function by clicking the Commissioning button in the upper right hand corner

of pID_Compact instruction box,

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SlTRAIN Training for Page 26 Pulse Width Modulation & PID ControllerAutomation and In6ustda~ Solutions

The Scope has buttons where you can start/stop the measurement and the ability to select the sampletime in ms through the provided sample time field.

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The Commissioning scope has several very useful features such as fix scale.

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The Commissioning scope has several very useful features such as the tool to Zoom in.

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SITRAIN Training for Page 29 Pulse W~dth Modulation & PID ControllerAulornalJon and Industrial Solutions

The Commissioning scope has several ve~ useful features such as the too[ to Zoom out.

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The Commissioning scope has several very useful features such as a window that displays the current

values.

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Commissioning

The Commissioning Scope has several features such as the auto tuner function which calculates the PiDloop tuning parameter then uploads them to the PID loop controller, Clicking the button in theoptimization window begins the process.

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SITRAIN Training for Page 32 Pulse Width Modulation & PID ControllerAutomation and Industrial Solutions

Commissioning - Kind of Commissioning

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]he auto tuner creates a step change in the process them monitors the response of the process todetermine to determine the PID loop tuning parameters. The step change causes the process to oscillateas illustrated in the graphic above and illustrated in the slides that follow.

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’ The auto tuner creates a step change in the process them monitors the response of the process todetermine the PID loop tuning parameters. After looking at the setpoint, input, and output, in the graphyou notice that the PID setpoint was changed and the PID input and PID output react to the change. Aprogress bar displays the progress time until the function is completed.

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"The step change causes the process to oscillate as illustrated in the graphic above.

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Commissioning - Online

The auto tuner calculates the PID tuning parameters then it stores them in PID_Compact data block that

has been associated with PID instruction.

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PID Exercise

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, Pulse Width Modulation (PWM)

,, PID Controller

¯ Exercise PID

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Page 37 Pulse W~dth Modulation & PID Controller

Exercise - PID Controller

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Hands-on

Let’s just do it ..... the lab for you

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Task

Process

Add new project

2.

3.4.5.

Click in the Task menu Project > New

Name the project ,,Project_exemise_PID_loop"Start "Add new device"Add "Unspecific CPU"Detect (upload) "hardware configuration"

S7-’1200 TIA SystemSITRAIN Training for Page 39 Pulse Width Modulation & PID ControllerAutomation and Industrial Solutions

Task

ProceSs

Define variable

6.Start Tag-Editor with a double click

7, Set up the displayed tags.

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Hands-on

Task

Process

Implement program code n Ma’n and add ’cycl’c OB’

9,10.

11.12,

13.14.15.

Open "Main" (OB1)Add program code like displayed

Add new block out of the project treeSelect "cyclic interrupt OB"

Type in the name "cyclic interrupt._PID controlleF’Give the OB the manual block number "300"Define the scan time with "lOOms"

Hit the Checkbox "Add new and open"

SITRAIN Training for $7-1200 TIA SystemAutomatlon and Industrial Solutions Page 41 Pulse Width Modulation & PID Controller

Task

Process

Add PID Controller

16.

17.18.

Add "PID_Compact" block out of the extended instructions

in the "cyclic interrupt_PID controller’ (OB300).Give the "InstanceDB / Technological object" a name.Add "Instance DB/Technological object" by hitting OK Button.

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Task

Process

Parameterize the PID Controller

19.20.21.22.23.24.25.

26.

Mark the "PID_Compact" blockSelect the point §basic settings"Select as controller type "Temperature"Select as unit "C°".Activate the checkbox "Invert PID-Controller output."Set the Set-point to "85."Select "Input_PER" for the Input value andtype in the variable "heat_sensor" (IW66),Select "OutpuLPER" for the Output value andtype in the variable "fan" (QWS0) an.

SITRAIN Training for $7-1200 TIA SystemAutomation and Industrial Solullons Page 43 Pulse Width Modulation & PID Controller

Exercise 8-1: Scale the InputsSIEMENS

Task Input scaling

Process 27.28.29.

30.

Select the point "input scaling".

Select for the Scaled upper value "100°C.’’

Select for the Scaled lower value "0°C."

Select for the analog/d{gital converter the values"0" for the lower limit and "27648" for the upper limit.

SITRAIN Training for $7-1200 T]A SystemAutomation and Industrial Solutions Page 44 Pulse Width Modulation & PID Controller

SIEMENSExercise 8-1: Download whole project

Hands-o~}

Task Download the whole project

Process 31.32.

"Save" the project.Download "All" to the PLC

SITRAIN Training for S7-1200 TIA SystemAutomation and Industrial Solutions Page 45 Pulse Width Modulation & PID Controller

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Task Commissioning the PID Controller

Process 33.34.

35.36.

Start the "Commissioning"Start the scope.Select "Tuning in run" and hit the "Start tuning" buttonAfter successful commissioning hit the button"Upload PID parameters to project" and save the project.

SITRAIN Training for $7-1200 TIA SystemAutomation and industrial Solutions Page 46 Pulse Width Modulation & PID Controller