PID Control for S7-300 and S7-400
Contents
1. iiia LMNR SIM LMNR_LS add LMNRS ON 00 0 LMNRSVAL 0 0 QLMNUP QLMNDN PULSE_TM 100 0 BREAK TM LMNS_ON Figure 3 2 Block Diagram of CONT_S Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 3 11 Function Blocks Input Parameters Table 3 3 contains the description of the input parameters for FB42 CONT S Table 3 3 Input Parameters INPUT for FB 42 CONT 5 Parameter Data Range of Default Description Type Values COM_RST BOOL COMPLETE RESTART The block has a complete restart routine that is processed when the input complete restart is set LMNR_HS BOOL HIGH LIMIT OF POSITION FEEDBACK SIGNAL The actuator at upper limit stop signal is connected to the high limit of position feedback signal input LMNR_HS TRUE means the actuator is at upper limit stop LMNR_LS BOOL LOW LIMIT OF POSITION FEEDBACK SIGNAL The actuator at lower limit stop signal is connected to the low limit of position feedback signal input LMNR_LS TRUE means the actuator is at lower limit stop LMNS_ON BOOL MANUAL ACTUATING SIGNALS ON The actuating signal processing is switched to manual at the manual actuating signals on input LMNUP ACTUATING SIGNALS UP With manual actuating value signals the output signal QLMNUP is set at the input actuating signals up LMNDN BOOL ACTUATING SIGNALS DOWN With manual actuating value signals2. 222 Period start iie i T Tm b PER TM EN PER_TM CYCLE of Synchronization PULSEGEN No synchronization of period start required PULSEGEN detects INV has e PULSEGEN detects INV has changed and the call is not in changed to 80 0 or 50 0 and the first or in the last two the call is in the first or in the cycles of a period last two cycles of the period Processing of PULSEGEN Processing of PULSEGEN in the first or in the last two cycles of the period Figure 3 5 Synchronization of the Period Start The automatic synchronization can be disabled at the SYN ON input FALSE Note With the beginning of a new period the old value of INV in other words of LMN is simulated in the pulse signal more or less accurately following the synchronization Standard Software for 57 300 and S7 400 PID Control C79000 G7076 C516 01 3 17 Function Blocks Modes Three Step Control 3 18 Depending on the parameters assigned to the pulse generator PID controllers with a three step output or with a bipolar or monopolar two step output can be configured The following table illustrates the setting of the switch combinations for the possible modes Switch MAN ON STEP3_ON ST2BI ON Mode Three step control FALSE TRUE Any Two step control with bipolar control FALSE FALSE TRUE range 100 to 100 Two step control with monopolar c
3. 100 INITIALIZATION VALUE OF THE INTEGRAL ACTION LITLVAL REAL 0 96 0 0 The output of the integrator can be set at input LITL_ON The or phys initialization value is applied to the input initialization value of value 2 the integral action 100 0 100 0 95 DISTURBANCE VARIABLE DISV REAL ir aie 0 0 For feedforward control the disturbance variable is connected to input disturbance variable value 2 1 Parameters in the setpoint and process variable branches with the same unit 2 Parameters in the manipulated value branch with the same unit Output Table 3 2 contains the description of the output parameters for FB41 Parameters CONT C Table 3 2 Output Parameters OUTPUT for 41 CONT C Data Range of t ME Type Values Default Description 0 0 MANIPULATED VALUE The effective manipulated value is output in floating point format at the manipulated value output LMN PER W 16 0000 MANIPULATED VALUE PERIPHERAL The manipulated value in the I O format is connected to the controller at the manipulated value peripheral output QLMN HLM FALSE HIGH LIMIT OF MANIPULATED VALUE REACHED The manipulated value is always limited to an upper and lower limit The output high limit of manipulated value reached indicates that the upper limit has been exceeded QLMN LLM FALSE LOW LIMIT OF MANIPULATED VALUE REACHED The manipulated value is always limited to an upper and lower limit The outpu
4. the output signal QLMNDN is set at the input actuating signals down PVPER ON PROCESS VARIABLE PERIPHERAL ON If the process variable is read in from the I Os the input PV PER must be connected to the I Os and the input process variable peripheral on must be set CYCLE ims SAMPLING TIME The time between the block calls must be constant The sampling time input specifies the time between block calls SP INT 100 0 100 0 INTERNAL SETPOINT 96 or phys value 1 PV_IN 100 0 100 0 PROCESS VARIABLE IN An initialization value can be set at the process variable in or phys value input or an external process variable in floating point format 1 can be connected The internal setpoint input is used to specify a setpoint PV_PER WORD W 16 0000 PROCESS VARIABLE PERIPHERAL The process variable in the I O format is connected to the controller at the process variable peripheral input Standard Software for S7 300 and S7 400 PID Control 3 12 C79000 G7076 C516 01 Function Blocks Table 3 3 Input Parameters INPUT for FB 42 CONT S Fortsetzung GAIN REAL 2 0 PROPORTIONAL GAIN The proportional gain input sets the controller gain TI TIME T 20s RESET TIME The reset time input determines the time response of the integrator DEADB_W REAL 0 0 100 0 or phys value 1 REAL 0 DEAD BAND W
5. BOOL TRUE _ If the input manual value on is set the control loop is interrupted A manual value is set as the manipulated value PROCESS VARIABLE PERIPHERAL ON If the process variable is read from the I Os the input PER must be connected to the I Os and the input process variable peripheral on must be set PROPORTIONAL ACTION ON The PID actions can be activated or deactivated individually in PVPER ON BOOL P_SEL BOOL the PID algorithm The P action is on when the input proportional action on is set INTEGRAL ACTION ON The PID actions can be activated or deactivated individually in SEL BOUE TRUE the PID algorithm The I action is on when the input integral action on is set FALSE TRUE INTEGRAL ACTION HOLD INT_HOLD BOOL FALSE The output of the integrator can be frozen by setting the input I ITL ON BOOL INITIALIZATION OF THE INTEGRAL ACTION The output of the integrator can be connected to the input I ITL VAL by setting the input initialization of the integral action on FALSE integral action hold DERIVATIVE ACTION ON The PID actions can be activated or deactivated individually in D_SEL POOL FALSE the PID algorithm The D action is on when the input derivative action on is set SAMPLING TIME CYCLE TIME gt ims 15 The time between the block calls must be constant The sampling time input specifies the time between block calls SP INT REAL PV IN REA
6. Describes the function blocks FB 41 _ FB 42 CONT S 3 and FB 43 PULSEGEN This manual is designed as a reference work providing you with the information you require about PID Control Depending on your experience you may well need further information that can be found in the manuals 70 100 101 231 232 234 If you have any questions regarding the use or application of PID Control please contact the Siemens representative in your area You will find a list of addresses in the Appendix SIEMENS Worldwide in the S7 400 Programmable Controller Hardware and Installation manual If you have any questions or comments on this manual please fill out the remarks form at the end of the manual and return it to the address shown on the form We would be grateful if you could also take the time to answer the questions giving your personal opinion of the manual Siemens also offers a number of training courses to introduce you to the SIMATIC 57 automation system Please contact your regional training center or the central training center in Nuremberg Germany for details Tel 49 911 985 3154 Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 Contents 1 Introduction 2 Parameter 3 Function Blocks 3 1 Continuous Control with FB41 CONT_C 3 2 Step Contr
7. converts the floating point value LMN to a peripheral value according to the following formula 27648 LMN_PER LMN 100 Feedforward Control A disturbance variable can be fed forward at the DISV input Complete Restart Restart FB41 CONT C has a complete restart routine that is run through when the input parameter COM RST TRUE is set During startup the integrator is set internally to the initialization value I ITVAL When it is called in a cyclic interrupt priority class it then continues to work starting at this value All other outputs are set to their default values The block does not check for errors internally The error output parameter RET VAL is not used Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 3 3 Function Blocks Block Diagram SP INT LMNLIMIT xlv LMN PER LMN HLM LMN FAC LMN LLM LMN OFF Figure 3 1 Block Diagram of CONT_C Standard Software for S7 300 and S7 400 PID Control 3 4 C79000 G7076 C516 01 Function Blocks Input Parameters Table 3 1 contains the description of the input parameters for FB41 CONT C Table 3 1 Input Parameters INPUT for FB 41 CONT C Parameter Data Range of Default Description Type Values COMPLETE RESTART COM RST BOOL FALSE The block has a complete restart routine that is processed when the input complete restart is set MANUAL VALUE ON
8. dead band width value 1 input determines the size of the dead band LMN LLM MANIPULATED VALUE HIGH LIMIT 100 0 96 The manipulated value is always limited by an upper and lower LMN HLM ERE ANS DE 2 or phys limit The manipulated value high limit input specifies the value 2 upper limit 100 0 MANIPULATED VALUE LOW LIMIT LMN HLM ris The manipulated value is always limited by an upper and lower LMN LLM 96 2 PERDE fO os i limit The manipulated value low limit input specifies the TEM lower limit value 2 PROCESS VARIABLE FACTOR PV FAC The process variable factor input is multiplied by the process variable The input is used to adapt the process variable range PROCESS VARIABLE OFFSET PV OFF The process variable offset input is added to the process variable The input is used to adapt the process variable range MANIPULATED VALUE FACTOR LMN FAC The manipulated value factor input is multiplied by the manipulated value The input is used to adapt the manipulated value range MANIPULATED VALUE OFFSET LMN OFF REAL 0 0 The manipulated value offset is added to the manipulated value The input is used to adapt the manipulated value range 3 6 Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 Function Blocks Table 3 1 Input Parameters INPUT for FB 41 CONT continued Parameter Data Default Description Type Values 100 0
9. loop controls as a cascade blending or ratio controller The functions of the controller are based on the PID control algorithm of the sampling controller with an analog signal if necessary extended by including a pulse generator stage to generate pulse duration modulated output signals for two or three step controllers with proportional actuators Description Apart from the functions in the setpoint and process value branches the FB implements a complete PID controller with continuous manipulated variable output and the option of influencing the manipulated value manually In the following you will find a detailed description of the subfunctions Setpoint Branch The setpoint is entered in floating point format at the SP INT input Process Variable Branch The process variable can be input in the peripheral I O or floating point format The IN function converts the PER peripheral value to a floating point format of 100 to 100 according to the following formula 100 Output of IN PV PER 27648 The PV NORM function normalizes the output of IN according to the following formula Output of PV NORM output of IN PV FAC PV OFF PV FAC has a default of and OFF a default of 0 Error Signal The difference between the setpoint and process variable is the error signal To suppress a small constant oscillation due to the manipulated variable quantization for examp
10. to QPOS P NEGATIVE PULSE ON In the manual mode with three step control the output signal QNEG P can be set at the input parameter negative pulse on In the manual mode with two step control QNEG P is always set inversely to QPOS P Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 Function Blocks Table 3 5 Input Parameters INPUT for FB 43 PULSEGEN continued Dat Type Range of Values Default Description BOOL TRUE SYNCHRONIZATION ON By setting the input parameter synchronization on it is possible to synchronize automatically with the block that updates the input variable INV This ensures that a changing input variable is output as quickly as possible as a pulse COM RST COMPLETE RESTART The block has a complete restart routine that is processed when the complete restart input is set T 10ms SAMPLING TIME The time between block calls must be constant The sampling time input specifies the time between block calls Note The values of the input parameters are not limited in the block There is no parameter check Output Parameters Table 3 6 Output Parameters OUTPUT for FB43 PULSEGEN Parameter Default Description QPOS P BOOL FALSE OUTPUT POSITIVE PULSE The output parameter output positive pulse is set when a pulse is to be output In three step control this is always the positive pulse In two step control QNEG P is a
11. Control continuous control with SEBA1 5 2 step control with FB42 Controller choosing CPU 314 IFM 2 1 41 _ block diagram B 4 FB41 CONT C 3 2 block diagram FB42 CONT_S block diagram 3 11 FB42 CONT 5 FB43 PULSEGEN block diagram 3 16 FB43 PULSEGEN automatic synchronization three step control three step control asymmetrical two step control Standard Software for 57 300 and S7 400 PID Control C79000 G7076 C516 01 Integrated control O Online help Parameter assignment user interface calling pl online help PID Control concept Process analysis Pulse duration modulation 1 1 3 15 PULSEGEN 3 15 S Step control 1 1 Index 1 Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 ox Siemens AG AUT E 146 stliche Rheinbr ckenstr 50 D 76181 Karlsruhe Federal Republic of Germany From Your Name Your Title Company Name Street City Zip Code Country Phone Please check any industry that applies to you Automotive Chemical Electrical Machinery Food Instrument and Control Nonelectrical Machinery 2 2 2 20 0000 Petrochemical Standard Software for 57 300 and S7 400 PID Control C79000 G7076 C516 01 LJ G y Pharmaceutical Plastic Pulp and Paper Textiles Transportation Other Remarks Form Your comments and recommen
12. D Control C79000 G7076 C516 01 Function Blocks Three Step Control Asymmetrical Duration of the Continuously A positive pulse ON PER TM PER TM P B TM 100 96 Continuously OFF Duration of the negative pulse Y Figure 3 6 Symmetrical Characteristic Curve of the Three Step Controller Ratio Factor 1 Using the ratio factor RATIOFAC the ratio of the duration of positive to negative pulses can be changed In a thermal process for example this would allow different system time constants for heating and cooling The ratio factor also influences the minimum pulse or minimum break time A ratio factor lt 1 means that the threshold value for negative pulses is multi plied by the ratio factor Ratio Factor 1 The pulse duration at the negative pulse output calculated from the input variable multiplied by the period time is reduced by the ratio factor see Figure 3 7 INV Duration of the positive pulse po PER TM INV Duration of the negative pulse PER TM RATIOFAC Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 3 19 Function Blocks Two Step Control 3 20 Duration of the positive pulse PER TM PER TM P B TM 0 5 P B TM 0 5 PER TM P B TM 0 5 PER TM Duration of the negative pulse Figure 3 7 Asymmetrical Characteristic Curve of the Three
13. IDTH A dead band is applied to the error The dead band width input determines the size of the dead band PROCESS VARIABLE FACTOR The process variable factor input is multiplied by the process variable The input is used to adapt the process variable range PROCESS VARIABLE OFFSET The process variable offset input is added to the process variable The input is used to adapt the process variable range PV OFF REAL 0 0 PULSE TM TIME 3 CYCLE T 3s BREAK_T TIME TH3s MTR_TM TIME T430s DISV REAL 100 0 100 0 0 0 96 or phys value 2 MINIMUM PULSE TIME A minimum pulse duration can be assigned with the parameter minimum pulse time MINIMUM BREAK TIME A minimum break duration can be assigned with the parameter minimum break time MOTOR ACTUATING TIME The time required by the actuator to move from limit stop to limit stop is entered at the motor actuating time parameter DISTURBANCE VARIABLE For feedforward control the disturbance variable is connected to input disturbance variable 1 Parameters in the setpoint and process variable branches with the same unit 2 Parameters in the manipulated value branch with the same unit Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 3 13 Function Blocks Output Parameters Table 3 4 contains the description of the output parameters for FB42 CONT S Table 3 4 Output Parameters OUTPU
14. L be connected W 16 00 PROCESS VARIABLE PERIPHERAL PV_PER WORD 00 The process variable in the I O format is connected to the controller at the process variable peripheral input 100 0 100 0 96 or phys INTERNAL SETPOINT The internal setpoint input is used to specify a setpoint value 1 100 0 100 0 PROCESS VARIABLE IN An initialization value can be set at the process variable in input or an external process variable in floating point format can or phys value 1 Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 3 5 Function Blocks Table 3 1 Input Parameters INPUT for FB 41 CONT continued Parameter Range of Default Description Values 100 0 100 0 96 MANUAL VALUE MAN BE The manual value input is used to set a manual value using the PS operator interface functions value 2 PROPORTIONAL GAIN GAIN B yis p The proportional value input specifies the controller gain RESET TIME TI The reset time input determines the time response of the integrator DERIVATIVE TIME TD The derivative time input determines the time response of the derivative unit TIME LAG OF THE DERIVATIVE ACTION TM LAG gt CYCLE The algorithm of the D action includes a time lag that can be assigned at the time lag of the derivative action input gt 0 0 96 DEAD BAND WIDTH DEADB W or phys A dead band is applied to the error The
15. OS output in steps of 10 The accuracy is increased as the number of FB PULSEGEN calls per CONT C call is increased If PULSEGEN is called for example 100 times more often than CONT C a resolution of 1 of the manipulated value range is achieved Note The call frequency must be programmed by the user It is possible to synchronize the pulse output with the block that updates the input variable INV for example CONT C This ensures that a change in the input variable is output as quickly as possible as a pulse The pulse generator evaluates the input value INV at intervals corresponding to the period PER TM and converts the value into a pulse signal of corresponding length Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 Function Blocks Since however INV is usually calculated in a slower cyclic interrupt class the pulse generator should start the conversion of the discrete value into a pulse signal as soon as possible after the updating of INV To allow this the block can synchronize the start of the period using the following procedure If INV changes and if the block call is not in the first or last two call cycles of a period the synchronization is performed The pulse duration is recalcu lated and in the next cycle is output with a new period see Figure 3 5 LMN INV 30 0 LMN INV 80 0 LMN INV 50 0 Processing of CONT_C CYCLEofCONTC
16. SIEMENS SIMATIC Standard Software for S7 300 and S7 400 PID Control User Manual C79000 G7076 C516 01 Preface Introduction Parameter Assignment Function Blocks References Glossary lindex Safety Guidelines AX Ax Qualified Personnel Correct Usage Trademarks This manual contains notices which you should observe to ensure your own personal safety as well as to protect the product and connected equipment These notices are highlighted in the manual by a warning triangle and are marked as follows according to the level of danger Danger indicates thatdeath severe personal injury orsubstantial property damage will resultif proper precautions are not taken Warning indicates thatdeath severe personal injury orsubstantial property damage can resultifproper precautions are not taken Caution indicates that minor personal injury or property damage can result if proper precautions are not taken Note draws yourattention to particularly importantinformation on the product handling the product orto a particular part of the documentation The device system may only be set up and operated in conjunction with this manual Only qualified personnel should be allowed to install and work on this equipment Qualified persons are defined as persons who are authorized to commission to ground and to tag circuits equipment and sys tems in accordance with establis
17. Step Controller Ratio Factor 0 5 Ratio Factor gt 1 The pulse duration at the positive pulse output calculated from the input variable multiplied by the period time is reduced by the ratio factor INV Duration of the negative pulse 100 x PER TM INV PER TM Durati f thi iti lse uration of the positive pulse 100 RATIOFAC In two step control only the positive pulse output QPOS P of PULSEGEN is connected to the on off actuator Depending on the manipulated value range being used the two step controller has a bipolar or a monopolar manipulated value range see Figures 3 8 and 3 9 Two Step Control with Bipolar Manipulated Variable Range 100 to 100 Duration of the pos pulse Continuously On PER_TM PER TM P B TM Continuously Off P B TM 100 0 0 0 100 0 Figure 3 8 Characteristic Curve with Bipolar Manipulated Value Range 100 96 to 100 96 Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 Function Blocks Manual Mode in Two Three Step Control Modes Error Information Two Step Control with Monopolar Manipulated Variable Range 0 to 100 Duration of the positive pulse PER_TM PER TM P B TM gt 0 0 96 100 0 Figure 3 9 Characteristic Curve with Monopolar Manipulated Value Range 0 96 to 100 96 The negated output signal is available at QNEG P
18. T for FB42 CONT S Parameter Data Range of Default Description Type Values QLMNUP BOOL FALSE ACTUATING SIGNAL UP If the output actuating signal up is set the actuating valve is opened QLMNDN BOOL FALSE ACTUATING SIGNAL DOWN If the output actuating signal down is set the actuating valve is opened PV REAL PROCESS VARIABLE The effective process variable is output at the process variable output ER REAL 0 0 ERROR SIGNAL The effective error is output at the error signal output 8 14 Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 Function Blocks 3 3 Pulse Generation with FB43 PULSEGEN Introduction Application Description FB43 PULSEGEN is used to structure a PID controller with pulse output for proportional actuators Using FB43 PULSEGEN PID two or three step controllers with pulse duration modulation can be configured The function is normally used in conjunction with the continuous controller CONT C CONT C PULSEGEN roe cce era mE ET m LATET The PULSEGEN function transforms the input variable INV manipulated value of the PID controller by modulating the pulse duration into a pulse train with a constant period corresponding to the cycle time at which the input variable is updated and which must be assigned in PER_TM The duration of a pulse per period is propo
19. _TM COM_RST CYCLE 5 P BE 3 26 Network 1 COM_RST M001 0 sCount CYCLE RED_FAC tCycCtr sCount 1 sCount 0 M002 CONT C COM_RST tCycCtr SP_INT _ RED_FAC sCount DI_CONT_C LMN DI_PULSEGEN INV DI_PULSEGEN tCycCtr COM_RST CYCLE QPOS_P Description Complete restart routine Calculate controller sampling time Decrement counter and compare with zero Conditional block call and set counter Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 References 70 100 101 231 232 234 350 Manual 57 300 Programmable Controller Hardware and Installation Reference Manual 7 300 M7 300 Programmable Controllers Module Specifications Manual 7 400 M7 400 Programmable Controllers Hardware and Installation Reference Manual 7 400 M7 400 Programmable Controllers Module Specifications User Manual Standard Software for 7 and M7 STEP 7 Manual Statement List STL for 57 300 and 57 400 Programming Programming Manual System Software for 57 300 and 57 400 Program Design User Manual SIMATIC S7 Standard Control Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 A 1 Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 Index A Applications C CONT C CONT 5 Continuous control 1 1
20. acy of the pulse duration modulation MINIMUM PULSE BREAK TIME A minimum pulse or minimum break time can be assigned at the input parameters minimum pulse or minimum break time RATIOFAC STEP3_ON ST2BI_ON MAN_ON TIME REAL BOOL BOOL RATIO FACTOR The input parameter ratio factor can be used to change the ratio of the duration of negative to positive pulses In a thermal process this would for example allow different time constants for heating and cooling to be compensated for example in a process with electrical heating and water cooling THREE STEP CONTROL ON The three step control on input parameter activates this mode In three step control both output signals are active TWO STEP CONTROL FOR BIPOLAR MANIPULATED VALUE RANGE ON With the input parameter two step control for bipolar manipulated value range on you can select between the modes two step control for bipolar manipulated value and two step control for monopolar manipulated value range The parameter STEP3_ON FALSE must be set MANUAL MODE ON By setting the input parameter manual mode on the output signals can be set manually POS_P_ON NEG_P_ON 3 22 BOOL BOOL BOOL POSITIVE PULSE ON In the manual mode with three step control the output signal QPOS_P can be set at the input parameter positive pulse on In the manual mode with two step control QNEG P is always set inversely
21. d resolution of the manipulated value by the actuator valve a dead band is applied to the error signal DEADBAND If DEADB W 0 the dead band is switched off Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 3 9 Function Blocks PI Step Algorithm The FB operates without a position feedback signal The I action of the PI algorithm and the assumed position feedback signal are calculated in one integrator INT and compared with the remaining P action as a feedback value The difference is applied to a three step element THREE ST and a pulse generator PULSEOUT that creates the pulses for the actuator The switching frequency of the controller can be reduced by adapting the threshold on of the three step element Feedforward Control A disturbance variable can be fed forward at the DISV input Modes Complete Restart Restart FB42 CONT 5 has a complete restart routine that is run through when the input parameter COM RST TRUE is set All other outputs are set to their default values Error The block does not check for errors internally The error output parameter Information RET VAL is not used Standard Software for S7 300 and S7 400 PID Control 3 10 C79000 G7076 C516 01 Function Blocks Block Diagram SP INT PVPER ON 1 PV IN CRP IN PV_PER DEADB W LMNLIMIT
22. dations will help us to improve the quality and usefulness of our publications Please take the first available opportunity to fill out this questionnaire and return it to Siemens Please give each of the following questions your own personal mark within the range from 1 very good to 5 poor Do the contents meet your requirements Is the information you need easy to find Is the text easy to understand Does the level of technical detail meet your requirements UP DET rA ba es Please rate the quality of the graphics tables Additional comments Standard Software for S7 300 and S7 400 PID Control 2 C79000 G7076 C516 01
23. e DBs that you assign to SFB41 or SFB42 Online help is available in the parameter assignment user interface to support you when you assign parameters to the controller blocks You can call the online help in three ways e Using the menu option Help Contents By pressing the F1 key Byclicking the Help button in the parameter assignment dialogs Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 2 1 Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 Function Blocks Chapter Overview Note The function blocks described in this chapter FB41 to FB43 have only been released for 57 C7 CPUs with cyclic interrupt levels Section Description Page 3 1 Continuous Control with FB41 CONT C 32 Step Control with FB42 5 3 9 3 3 Pulse Generation with FB43 PULSEGEN 3 4 Example of Using PULSEGEN 3 24 Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 3 1 Function Blocks 3 1 Continuous Control with FB41 C Introduction FB CONT is used on SIMATIC 7 programmable controllers to control technical processes with continuous input and output variables During parameter assignment you can activate or deactivate subfunctions of the PID controller to adapt the controller to the process Application You can use the controller as a PID fixed setpoint controller or in multi
24. ections can be seen in Figure 3 11 During a complete restart the block PULS is called in OB100 and input COM RST is set to TRUE Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 Function Blocks OB 100 Complete restart OB 35 10ms PULS CTR DPULS TRUE 100 FB 50 DB 50 FALSE OB35 T 10ms CYCLE 200 RED FAC PULS CTR DPULS CTR FB 50 DB 50 COM RST RED FAC X CONTE PULSEGE SP_INT Poari COM RST QPOS P QPOS P SPINT CYCLE PV_PER PV_PER EMN TM L INV CONT C call reduced by RED FAC Figure 3 11 Block Call and Interconnection STL Program for FB PULS CTR Table 3 7 FB PULS CTR Address Declaration Name Type Comment REAL Sepo Process variable in periph format INT Call reducing factor BOOL Complete restart 4 0 TIME Sampling time BOOL Actuating signal 16 0 FB CONT_C Counter 142 0 FB PULSEGEN Counter 176 0 INT Counter TIME Controller sampling time ALSO w Standard Software for 57 300 57 400 PID Control C79000 G7076 C516 01 3 25 Function Blocks Table 3 8 STL JCN CALL COM RST CYCLE SP INT PV PER L T M002 L T CALL PER
25. hed safety practices and standards Note the following Warning This device and its components may only be used forthe applications described in the catalog orthe technical description and only in connection with devices or components from other manufacturers which have been approved or recommended by Siemens This productcan only function correctly and safely if itis transported stored setup and installed correctly and operated and maintained as recommended SIMATIC amp and SINEC O are registered trademarks of SIEMENS Third parties using for their own purposes any other names in this document which refer to trademarks might infringe upon the rights of the trademark owners Copyright Siemens AG 1996 All rights reserved The reproduction transmission oruse ofthis documentor its contents is not permitted withoutexpress written authority Offenders will be liable for damages Allrights including rights created by patentgrantorregistration of a utility model or design are reserved Siemens AG Automation Group Industrial Automation S ystems Postfach 4848 D 90327 N rnberg Disclaimer of Liability We have checked the contents of this manual for agreement with the hardware and software described S ince deviations cannotbe precluded entirely we cannot guarantee full agreement However the data in this manualare reviewed regularly and any necessary corrections included in subsequent editions Suggestions for i
26. if the connection of the two step controller in the control loop requires a logically inverted binary signal for the actuating pulses Actuator Off Pulse QPOS P TRUE FALSE QNEG P FALSE TRUE In the manual mode MAN_ON TRUE the binary outputs of the three step or two step controller can be set using the signals POS_P_ON and NEG_P_ON regardless of INV wear on Three step control FALSE FALSE TRUE FALSE FALSE TRUE FALSE FALSE Two step control FALSE Any FALSE TRUE TRUE Any TRUE FALSE Complete Restart Restart During a complete restart all the signal outputs are set to 0 The block does not check for errors internally The error output parameter RET_VAL is not used Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 3 21 Function Blocks Input parameters Table 3 5 Parameter INV PER TM B TM Input Parameters INPUT for FB 43 PULSEGEN Range of Values Default Description Type 100 0 100 0 REAL TIME gt 20 CY CLE T 50ms INPUT VARIABLE An analog manipulated value is connected to the input parameter input variable PERIOD TIME The constant period of pulse duration modulation is input with the period time input parameter This corresponds to the sampling time of the controller The ratio between the sampling time of the pulse generator and the sampling time of the controller determines the accur
27. le in pulse duration modulation with PULSEGEN a dead band is applied to the error signal DEADBAND If DEADB_W 0 the dead band is switched off PID Algorithm The PID algorithm operates as a position algorithm The proportional integral INT and derivative DIF actions are connected in parallel and can be activated or deactivated individually This allows P PI PD and PID controllers to be configured Pure I and D controllers are also possible Standard Software for S7 300 and S7 400 PID Control 3 2 C79000 G7076 C516 01 Function Blocks Modes Error Information Manual Value It is possible to switch over between a manual and an automatic mode In the manual mode the manipulated variable is corrected to a manually selected value The integrator INT is set internally to LMN LMN P DISV and the derivative unit DIF to 0 and matched internally This means that a switchover to the automatic mode does not cause any sudden change in the manipulated value Manipulated Value The manipulated value can be limited to a selected value using the LMNLIMIT function Signaling bits indicate when a limit is exceeded by the input variable The LMN NORM function normalizes the output of LMNLIMIT according to the following formula LMN output of LMNLIMIT LMN FAC LMN OFF LMN FAC has the default 1 and OFF the default 0 The manipulated value is also available in the peripheral format The CRP OUT function
28. lways set inversely to QPOS P QNEG P BOOL FALSE OUTPUT NEGATIVE PULSE The output parameter output negative pulse is set when a pulse is to be output In three step control this is always the negative pulse In two step control QNEG is always set inversely to QPOS Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 3 23 Function Blocks 3 4 Example of Using PULSEGEN Control Loop Using the continuous controller CONT C and the pulse generator PULSEGEN you can implement of fixed setpoint controller with a switching output for proportional actuators Figure 3 10 illustrates the basic signal sequence in the control loop CONT C PULSEGEN LMN INV nana QPOS_P H QNEG P JuuuL 1PV PER Loop with switching output Figure 3 10 Control Loop Block call and Connection 3 24 The continuous controller CONT forms the manipulated value LMN that is converted to pulse break signals QPOS_P or QNEG P by the pulse generator PULSEGEN The fixed setpoint controller with a switching output for proportional actuators PULS CTR consists of the blocks CONT C and PULSEGEN The block call is implemented so that CONT C is called every 2 seconds CYCLE RED FAC PULSEGEN every 10 ms CYCLE The cycle time of OB35 is set to 10 ms The conn
29. mprovement are welcomed Technical data subject to change Siemens AG 1996 Siemens Aktiengesellschaft C79000 G7076 C516 Preface Purpose Audience Structure of PID Control This manual supports you when working with the controller blocks of PID Control The manual introduces you to the functions of the controller blocks and familiarizes you with the user interface for assigning parameters to the blocks This user interface includes online help that further supports you when assigning parameters to the blocks This manual is intended for the following readers 57 programmers Programmers of closed loop control systems Operators Service personnel PID Control 57 300 and 57 400 Function Parameter blocks assignment user PID Control interface PID Control PID Control The PID Control software package includes the following components The function blocks CONT C CONT 5 and PULSEGEN The parameter assignment user interface for configuring the controller blocks The manual consisting mainly of a description of the function blocks Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 Preface Content of the Manual Further Information Additional Assistance Chapter Provides you with an overview of PID Control IN Chapter Explains how to call the parameter assignment user interface 2 A Chapter
30. ol with FB42 CONT_S 3 3 Pulse Generation with FB43 PULSEGEN 3 4 Example of Using PULSEGEN HRACE 348 0 000 meer z Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 Standard Software for 57 300 and S7 400 PID Control C79000 G7076 C516 01 Introduction The Concept of PID Control Basic Functions Applications Process Analysis The function blocks FBs of the PID Control package consist of controller blocks for continuous control CONT C for step control CONT S and the FB for pulse duration modulation PULSEGEN The controller blocks implement a purely software controller with the block providing the entire functionality of the controller The data required for cyclic calculation is stored in data blocks assigned to the FB This allows the FBs to be called as often as necessary FB PULSEGEN is used in conjunction with FB CONT to implement a controller with a pulse output for proportional actuators A controller created with the FBs consists of a series of subfunctions that you can activate or deactivate In addition to the actual controller with its PID algorithm integrated functions are also available for processing the setpoint and process variable and for adapting the calculated manipulated variable A controller implemented with the two controller blocks is not restricted to any particular application The performance of the controller and its proces
31. oller or in secondary control loops in cascade blending or ratio controllers however not as the primary controller The functions of the controller are based on the PI control algorithm of the sampling controller supplemented by the functions for generating the binary output signal from the analog actuating signal Apart from the functions in the process value branch the FB implements a complete PI controller with a digital manipulated value output and the option of influencing the manipulated value manually The step controller operates without a position feedback signal In the following you will find the description of the partial functions Setpoint Branch The setpoint is entered in floating point format at the SP INT input Process Variable Branch The process variable can be input in the peripheral I O or floating point format The IN function converts the PV PER peripheral value to a floating point format of 100 to 100 according to the following formula 100 Output of IN PV PER 27648 The PV_NORM function normalizes the output of CRP_IN according to the following formula Output of PV NORM output of CRP_IN PV FAC PV OFF PV FAC has a default of and OFF a default of 0 Error Signal The difference between the setpoint and process variable is the error signal To suppress a small constant oscillation due to the manipulated variable quantization for example due to a limite
32. ontrol FALSE FALSE FALSE range 0 100 Manual mode TRUE Any Any In the three step control mode the actuating signal can adopt three states The values of the binary output signals QPOS_P and QNEG P are assigned to the statuses of the actuator The table shows the example of a temperature control Actuator Heat Off Cool Output signal QPOS P TRUE FALSE FALSE FALSE QNEG P FALSE TRUE Based on the input variable a characteristic curve is used to calculate a pulse duration The form of the characteristic curve is defined by the minimum pulse or minimum break time and the ratio factor see Figure 3 6 The normal value for the ratio factor is 1 The doglegs in the curves are caused by the minimum pulse or minimum break times Minimum Pulse or Minimum Break Time A correctly assigned minimum pulse or minimum break time P B TM can prevent short on off times that reduce the working life of switching elements and actuators Note Small absolute values at the input variable LMN that could otherwise generate a pulse duration shorter than P B TM are suppressed Large input values that would generate a pulse duration longer than PER TM P B TM are set to 100 96 or 100 96 The positive and negative pulse duration is calculated by multiplying the input variable in 96 with the period time INV x PER TM 100 Pulse duration Standard Software for S7 300 and S7 400 PI
33. rtional to the input variable The cycle assigned to PER_TM is not identical to the processing cycle of the FB PULSEGEN The PER_TM cycle is made up of several processing cycles of FB PULSEGEN whereby the number of FB PULSEGEN calls per PER TM cycle is the yardstick for the accuracy of the pulse duration modulation INV 100 4 LMN ol 50 50 30 0 gt QPOS P 0 gt t PULSEGEN cycle lt PER TM gt CONT C cycle Figure 3 3 Pulse Duration Modulation Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 3 15 Function Blocks Block Diagram Accuracy of the Manipulated Value Automatic Synchronization 3 16 An input variable of 30 and 10 PULSEGEN calls per PER TM means the following One at the QPOS output for the first three calls of FB PULSEGEN 30 of 10 calls Zero at the QPOS output for seven further calls of FB PULSEGEN 7096 of 10 calls POS P ON NEG P ON STEP3 ON SYN_ON i ST2BI_ON PER TM P RATIOFAC Figure 3 4 Block Diagram of PULSEGEN With a sampling ratio of 1 10 CONT_C calls to PULSEGEN calls the accuracy of the manipulated value in this example is restricted 010 in other words set input values INV can only be simulated by a pulse duration at the QP
34. sing speed is only dependent on the performance of the CPU being used With any given CPU a compromise must be made between the number of controllers and the frequency at which the individual controllers are processed The speed at which the control loops must be processed in other words the more often the manipulated variables must be calculated per unit of time determines the number of controllers that can be installed faster loops mean less controllers There are no restrictions in terms of the type of process that can be controlled Both slow processes temperatures tank levels etc and very fast processes flow rate motor speed etc can be controlled Note The static behavior gain and the dynamic characteristics time lag dead time reset time etc of the process to be controlled have a significant influence on the structuring and design of the controller and on the selection of the dimensions of its static P component and its dynamic I and D components parameters Precise knowledge of the type and characteristic data of the process to be controlled is essential Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 Introduction Choice of Controller Note The characteristics of control loops are decided by the given physical characteristics of the process or machine being controlled and can only be modified in minor ways Good control quality is only possible if you choose
35. t low limit of manipulated value reached indicates that the lower limit has been exceeded LMN P 0 0 PROPORTIONAL COMPONENT The proportional component output contains the proportional component of the manipulated variable LMN I REAL 0 0 INTEGRAL COMPONENT The integral component output contains the integral component of the manipulated value LMN D REAL 0 0 DERIVATIVE COMPONENT The derivative component output contains the derivative component of the manipulated value Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 3 7 Function Blocks Table 3 2 Parameter PV ER Output Parameters OUTPUT for FB 41 continued PROCESS VARIABLE The effective process variable is output at the process variable output ERROR SIGNAL The effective error is output at the error signal output 3 8 Standard Software for S7 300 and S7 400 PID Control C79000 G7076 C516 01 Function Blocks 3 2 Step Control with FB42 S Introduction Application Description FB42 CONT 5 is used on SIMATIC 57 programmable logic controllers to control technical processes with digital manipulated value output signals for integrating actuators During parameter assignment you can activate or deactivate subfunctions of the PI step controller to adapt the controller to the process You can use the controller as a PI fixed setpoint contr
36. the controller type most suited to your situation and adapt it to the time response of the process Creating the You can create a controller structuring parameter assignment and call in Controller the system program largely without programming Knowledge of STEP 7 is however necessary Online Help The STEP 7 online help also provides you with information about the various FBs Further PID Control is a subset of Standard Control For further information about Information the standard controller refer to 350 Standard Software for S7 300 and S7 400 PID Control 1 2 C79000 G7076 C516 01 Parameter Assignment Calling the Parameter Assignment User Interface Online Help You call the parameter assignment user interface of PID Control under Windows 95 using the following menu options Start SIMATIC STEP 7 PID Control Parameter Assignment In the first dialog you can either open an existing instance data block DB for an FB41 CONT C or FB42 S or create new data block as the instance data block If you create a new instance data block you will be prompted to assign the instance DB to an FB FB43 PULSEGEN does not have a parameter assignment user interface You must set its parameters with STEP 7 tools Note Using the parameter assignment user interface of PID Control you can also assign parameters for the integrated control of the CPU 314 IFM In this case you create instanc
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