1 / 54

Lecture 8

Lecture 8. Clock-Mode Sequential Machines Gas burner start up (application example). Clock-Mode Sequential Machines. 8.1 Introduction 8.2 Mealy and Moore machine 8.3 State table 8.4 State diagram. Gas burner start up (application example). 8.5 Introduction 8.6 Technological conditions

oliver
Download Presentation

Lecture 8

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 8 Clock-Mode Sequential Machines Gas burner start up (application example)

  2. Clock-Mode Sequential Machines • 8.1 Introduction • 8.2 Mealy and Moore machine • 8.3 State table • 8.4 State diagram

  3. Gas burner start up (application example) • 8.5 Introduction • 8.6 Technological conditions • 8.7 Variable list • 8.8 Block diagram of the whole system • 8.9 Minimal HW configurationof a PLC • 8.10 State diagram

  4. 8.1 Introduction The various flip-flops, counters and shift registers are all examples of sequential machines (automatons). All these circuits contain memory elements. The flip-flops are the elementary memory elements. The counters and shift registers are composed of more than one such element.

  5. Introduction -2 All the circuit are capable of assuming more than one state. Their outputs do not depend only on the inputs but also on the state in which the circuit is at the time when the input is acting on it. If we note carefully the circuits of all these elements, they have a feedback from the output to the input.

  6. 8.2 Mealy and Moore machine In general, a sequential machine will have the following: 1. A set S containing a finite number, say p, of internal states, so that S={S1, S2,……Sp} 2. A set X having a finite number, say n, of inputs, so that X={X1, X2,……Xn} 3. A set Z containing a finite number, say m, of outputs, so that Z={Z1, Z2,……Zm}

  7. Mealy and Moore machine-2 • A characterizing function f that uniquely defines the next state St+1 as a function of the present state St and the present input Xt , so that St+1 = f(St , Xt )

  8. Mealy and Moore machine-3 5.A Mealy machine A characterizing function gthat uniquely defines the output Zt as a function of the present input Xt and the present internal state St , so that Zt = g(St , Xt )

  9. Mealy and Moore machine-4 5.B Moore machine A characterizing function gthat uniquely defines the output Zt as a function of the present internal state St , so that Zt = g(St )

  10. Mealy and Moore machine-5 A sequential machine can therefore formally be defined as follows: Definition: A sequential machine is a quintuple, M=(X,Z,S,f,g), where X, Z and S are the finite and nonempty sets of inputs, outputs, and states respectively.

  11. Mealy and Moore machine-6 f is the next-state function, such that St+1 = f(St , Xt ) and the g is the output function such that Zt = g(St , Xt ) for a Mealy machine Zt = g(St ) for a Moore machine To describe a sequential machine, either a state table or a state diagram is used.

  12. 8.3 State table Table1 is a state table describing an example sequential machine M1. It can be seen that machine M1 has a set of four internal states A,B,C and D, a set of two inputs I1 and I2 and a set of outputs O1 ,O2 The characterizing functions f and g are depicted in tabular form, which is the state table.

  13. State table-2 • State table of a Mealy machine M1

  14. State table-3 For example, for the present state B when the input is I1, the next state is D and the output is O2. If the input is I2, the next state is A and the output is O1. Thus the table shows the next state and the output for each combination of the present state and the input. Since the output of the machine M1 depends on both the present state and the input, it is a Mealy machine.

  15. State table-4 Table2 shows the state table of a Moore machine. Here the output is independent of the input and depends only on the present state of the machine. Therefore, this table has a separate column defining the outputs, and two input columns defining the next state without having any output associated with it.

  16. State table-5 • State table of a Moore machine M2

  17. State table-6 Another interesting property of of the machines M1, M2 which we have depicted in the two state tables is that for all combinations of present state and input, the next state and the output are completely specified. Such machines are therefore called completely specified sequential machines (CSSMs).

  18. State table-7 There is another clas of sequential machines, where sometimes the next state or the output or both may remain unspecified. Such machines are known as incompetely specified sequential machines (ISSMs).

  19. 8.4 State diagram The information contained in the state table can also be shown in a graphical manner with the help of nodes conected by directed graphs. Such diagrams are called state diagrams. Folowing figures show the state diagrams of machines M1 and M2 respectively.

  20. State diagram-2 State diagram of the Mealy machine M1

  21. State diagram-3 State diagram of the Moore machine M2

  22. Literature • Nripendra N. Biswas: Logic Design Theory,Prentice Hall International,1993,ISBN 0-13-010695-X

  23. Gas burner start up (application example)

  24. 8.5 Introduction • Both startup and shut down of a gas burner is rather complicated by safety reason • There is a risk of explosion for example at gas escape, premature ignition (firing), lighting out of the flame when the gas valve is open etc. • The right startup sequence given by standards • Simplified in our example • Moore machine application

  25. 8.6 Technological conditions At the beginning waiting for Start signal from thermostat Initial checking: • Air pressure sensor checking • (there must not be the air overpressure) • Gas pressure sensor checking • (there must be sufficient gas pressure)

  26. Technological conditions-2 After the initial checking: Startup of the combustion air compressor and after it the delay τ2=3 s (air compressor is running with sufficient performance) Ventilating of the combustion chamber during τ1=30 s (to prevent creating of detonating mixture from the rest of gas and the air) Checking of sufficient ventilating of the combustion chamber(sufficient high value at the air pressure sensor)

  27. Technological conditions-3 After the sufficient ventilating the burner firing startup: • Gas valve opening • Firing signal generation (e.g. pulses) • Continuing with these conditions during τ3=4 s • After this delay expiration standard operating checking starts

  28. Technological conditions-4 Standard operating checking sequence Gas pressure sensor checking -(there must be sufficient gas pressure) Air pressure sensor checking -(there must be sufficient air overpressure) Flame presence sensor checking -(the flame must not disappear when gas valve is open) Thermostat checking -(is there a need for heating, that is for running the burner?)

  29. Technological conditions-5 Shut down of the gas burner • Similar sequence as with start up • Here not in detail, only one macro state „shut down“ Errors • When any error occures during start up,standard operating or shut down, then it is necessary to assure properly transition to the error state (shut down and the error message)

  30. 8.7 Variable list Inputs of PLC • Sta…..thermostat (there is a need for heating: Sta=1) • Vzd …air pressure sensor (sufficient pressure : Vzd=1) • Ply … gas pressure sensor (sufficient pressure : Ply=1) • Pla …. flame presence sensor (flame is burning: Pla=1)

  31. Variable list-2 Outputs of PLC • Sdv ……air compressor (Sdv=1: air compressor start up!) • Opp ….. gas valve (Opp =1: gas valveopen!) • Zps …. firing signal (Zps=1: firing signal generation!)

  32. Variable list-3 Internal variables – technological parameters • τ1 …delay for ventilating of the combustion chamber (τ1=30s ) • τ2…delayfor combustion air compressor starting (τ2=3s ) • τ3… delayforfiring signal generation (τ3=4s )

  33. PLC I O 8.8 Block diagram of the whole system Pla TP Ply Sta Vzd TP ……technological process ( gas burner )

  34. PLC I O Block diagram of the whole system-2 Pla TP Ply Sta Vzd

  35. PLC I O Block diagram of the whole system-3 Sdv Pla ŘS TP Ply Opp Sta Zps Vzd

  36. PLC I O Block diagram of the whole system-4 Sdv Pla ŘS TP Ply Opp Sta Zps Vzd τ1, τ2, τ3

  37. PLC I O Block diagram of the whole system-5 OP OP Operator panel Rest Err Sdv Pla ŘS TP Ply Opp Sta Zps Vzd τ1, τ2, τ3

  38. Variable list- inputs and outputs of PLC Inputs of PLC • Sta…..thermostat (there is a need for heating: Sta=1) • Vzd …air pressure sensor (sufficient pressure : Vzd=1) • Ply … gas pressure sensor (sufficient pressure : Ply=1) • Pla …. flame presence sensor (flame is burning: Pla=1) • Rest …..OP – restarting command (command for restarting from operator panel: Rest=1)

  39. Variable list- inputs and outputs Outputs of PLC • Sdv ……air compressor (Sdv=1: air compressor start up!) • Opp ….. gas valve (Opp =1: gas valveopen!) • Zps …. firing signal (Zps=1: firing signal generation!) • Err …..OP – error indication lamp (Err=1: lamp is on!)

  40. 8.9 Minimal HW configuration of a PLC • 5 binaryinputs +20% reserve…6 DI • 4 binaryoutputs +20% reserve..5 DO • DI ..Digital Input • DI ..Digital Output • real configuration: 8/8 IO [ajou] • binaryinputs and outputs of PLC often organised in groups of 4, 8, 16 • specific addresses are HW dependend, (IEC 1131: inputs - I, outputs – Q)

  41. Tau1 Tau2 8.10 State diagram Opp, Sdv En? Sta Start up: CNS to ZAP CNS K01 ODS Vzd Sta Vzd Ordinary operation: K04 až K07 Rest K07 K07 K02 Ply ERR 1 Pla Ply 2 Shut down: „makrostate“ ODS Pla K06 K06 6 Sdv C1 C1 5 Vzd 3 4 Vzd Vzd K05 K05 Ply Tau2 Errors: „macrostate“ ERR C2 C2 Tau1 Tau3 Sta K04 Ply ZAP Tau3 Opp,Zps Zps

  42. State diagram-2 Sta CNS State names: K01 CNS..waiting for start K01..first checking

  43. State diagram-3 Sta CNS CNS State names: K01 K01 Vzd K02..second checking Vzd K02 ERR..error ERR Vzd ... direct variable (=1) Vzd ...inverse variable (=0)

  44. State diagram-4 Sta CNS CNS State names : K01 K01 Vzd C1…first waiting loop Vzd K02 K02 Ply ERR Ply Sdv C1 blue ..outputs, only when changing

  45. Sta CNS CNS CNS K01 K01 K01 Vzd Vzd K02 K02 Ply ERR ERR Ply Sdv C1 C1 Tau2 Tau2 C2 State diagram-5 State names: C2…second waiting loop green auxiliary binary variables (with the relation to the technological parametres) t< τ2: Tau2=0 …. Tau2 t τ2: Tau2=1 …. Tau2 Implementation in PLC with „timers“

  46. Tau1 Tau2 State diagram-6 Sta CNS State names: K01 Vzd Vzd ZAP...burner firing K02 Ply ERR Ply Sdv C1 Vzd Tau2 C2 Tau1 ZAP Opp,Zps

  47. Tau1 Tau2 State diagram-7 Sta CNS State names: K01 Vzd K04…fourth checking Vzd K02 Ply ERR Ply Sdv C1 Vzd Tau2 C2 Tau1 K04 Tau3 ZAP Opp,Zps Zps Tau3

  48. Tau1 Tau2 K04 State diagram-8 Sta CNS State names: K01 Vzd Vzd K05…fifth checking K02 Ply ERR Ply Sdv C1 C1 Vzd K05 Ply Tau2 C2 C2 Tau1 Tau3 Ply ZAP Opp,Zps Tau3 Zps

  49. Tau1 Tau2 K04 State diagram-9 Sta CNS State names: K01 Vzd K06…sixth checking Vzd K02 Ply ERR Ply K06 Sdv C1 C1 Vzd Vzd Vzd K05 K05 Ply Tau2 C2 C2 Tau1 Tau3 Ply ZAP Zps Opp,Zps Tau3

  50. Tau1 Tau2 K04 State diagram-10 Sta CNS State names: K01 Vzd K07…seventh checking Vzd K07 K02 Ply ERR Pla Ply Pla K06 K06 Sdv C1 C1 Vzd Vzd Vzd K05 K05 Ply Tau2 C2 C2 Tau1 Tau3 Ply ZAP Zps Opp,Zps Tau3

More Related