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i\t CONFIDENTIAL HM Universitl lUn Hussein Onn Malaysia T]NIVERSITI TUN HUSSEIN ONN MALAYSIA FINAL EXAMINATION SEMESTER sEssroN II 201s12016 COURSENAME PROCESS CONTROL COURSE CODE BNQ 30703 PROGRAMME CODE BNN EXAMINATIONDATE JUNE IJULY 2016 DURATION 3 HOURS INSTRUCTION ANSWERS FOUR (4) QUESTIONS ONLY THrS QUESTTON pApER CONSTSTS OF FOURTEEN (14) PAGES CONFIDENTLq..L CONFIDENTIAL Ql (a) BNQ 30703 List SIX (6) basic components in a feedback control loop system. (3 marks) (b) Briefly describe process gain, K. (3 marks) (c) hopose controllers which fulfills the following requirement and provide relevant explanation. The reactor is a continuous flow stined tank reactor (CSTR), in which the controlled variable is the liquid volume. It is extremely important that the volume is at the set point, the system provides a quick respond to changes in the set point, and large error is not allowed. (3 marks) (d) Figure Ql(d) shows a level confoller in a CSTR. Explain how the liquid level contoller controls the level of the fluid within the CSTR by using the details given in the figure. (6 marks) Controller Error ; Set Point Measured Signal Figure Ql(d) CONFIDENTIAL t | r( CONFIDBNTIAL (e) BNe3o7o3 Consider a continuous flow stined tank reactor (CSTR) with a feedback controller where the controlled variable is the liquid level with the following transfer functions. G" =l(s+l) G"=IG Gp:1(2s+l) G':l(s+l) Go:1 where G is the conffoller ffansfer function G" is the transfer function for final control element Go is the process transfer function G, is the transfer function for measuring element and transmitter Ga is the disturbance transfer function Analyze the range oflGwhich makes the closed loop response stable. Neglect the effect ofdisturbances. (10 marks) Q2 (a) The Proportional-integral-derivative (PID) controller algorithm involves simple calculations. Describe the importance of the calculations during the development of the algorithm and for the practice of process control. (2 marks) (b) Identiff the units of Kc (c) A PID controller must be initialized every time it is "tumed on" (or placed in automatic mode) by the plant personnel. Data when the conftoller is placed in automatic mode are given below. and the sign for stabilizing negative feedback. (4 marks) Data Set point: 100 oC oC Measured controlled variable = 98 Derivative of the controlled variable = 0 Signal to control valve 63.7 Yo open Controller Gairu Kc = 230 o/ol"C Controller integral time 4.50 minutes Controller derivative time: 0.67 minutes : : (i) State the type of transfer (ii) Perform the initialization calculation. (1 mark) (5 marks) CONFIDENTIAL CONFIDENTIAL (d) BNQ 30703 The feedback PID controller has been implemented to control the concenfration of the reactant in the reactor effluent from a CSTR. The system is shown in Figure Q2(d) below. ft*,rg*istrI Solu*nt r{" ,** B ,i *fa '* }r C* ffi,Fs inmcfiffit Sffis filBrt*nt f* mhF* F*#& Figure Q2(d) (i) causes for the feedback dynamics to change in the process in Figure indicated Q2(d). For each causes, examine how the change affects Identiff the the dynamics. (4 marks) (ii) One of the major reasons for feedback control is to compensate for disturbances. Analyze several disturbances that would affect the reactant concentration. (4 marks) (e) Describe the advantages and disadvantages control system. of distributed computing in a digital (3 marks) (0 successful feedback control systems, the objective for the manipulated variable must be fully understand. State the objective forthe manipulated variables and briefly describe the importance. (2 marks) In order to design CONFIDENTIAL CONTIDENTIAL Q3 (a) BNQ 30703 (D Define'block diagram'. (ii) f,haw a block and arrows diagram consists of a single block with one input and one output. (l (l (b) Figure Q3 (b) below shows a tank mark) mark) with two inlet flows. Figure Q3 (b) The liquid level ofthe tank is to be confrolled by manipulating (controlling) flow A. It is assumed that flow A is much larger than flow B. The ratio between flow B and A is specified ag FnlFt = fr, where f is a given ratio. Assume that it is necessary to have local flow contnol loops around each valve. Illustate a process diagram ofa control system for this process. (4 marks) CONFIDENTIAL CONFIDENTIAL (c) BNQ 30703 A block diagram is shown in Figure Q3(c) below. Figure Q3(c) IrA. (i) Develop a single tansfer function from input Ytpzto output Yz, assuming (2 marks) (ii) If the inner loop has proportional-only controller for Gcz, and G, : 3, and Gp2(s):6 | (2s+1), calculate a oonstraint (inequaltty) for the value of .Kcso that the inner loop still has stable behaviour. (4 marks) CONFIDENTIAL CONFIDENTIAL (d) BNQ 30703 Figure Q3(d) below shows a heated liquid tank where the temperature T shall be controlled using feedback with PID controller in combination with feedforward control. P,,..fffiffi's};i' .,f'[ffi.,.,, ffiffi:'fi--" S :::irts::,:+ii,iijiii#i:j+#' ,ffin.eo ,ll-,.T.[ffi.,;[,€l #ry Figure Q3(d) We assume the following process model, which is based on energy balance: cpt't(t1 = gy1} * cre 1l',{fi - ?'{t)i = r [&{t) - r(t)} P ofthe liquid in the tank, fn[Kl is the inlet temperature, fe lK)is environmental temperature, c [y(kg K)] is specific heat capacity, w [kg/s] is mass flow (same in as out), V lm3l is the liquid volume, p Ikglm3l is the liquid density, U t(J/s)/Kl is the total heat transfer coeflicient, P: Knu [J/min] is supplied power via heating element where Knis aparameter (gain) and u [%] is the control signal applied to the heating element. cpV T is the (temperature dependent) energy of the liquid in the tank. Consider Tin and ?e as disturbances, but the derivation of the feedforward function F/is not dependent of such a classification. Where T (D [K] is the temperature Derive the feedforward function from the process model above. (6 marks) (ii) Distinguish which parameters and variables must have known values to implement the feedforward control. (2 marks) COI{FIDENTIAL CONFIDBNTIAL (e) BNQ 30703 Given a system with the following equatiotr, Mx: F-dx-lu where ? is the position is the speed is the acceleration x x Fis the force (control signal, z) d and k are constants Develop a block diagram for the system. (3 marks) (D Recommend the correct equivalent ofthe block diagram given in Figure Q3(f) below. (2 Q4 (a) (i) (iD Define 'cascade control'. State when cascade control marks) (l will give improved performance mark) than conventional feedback control. (1 mark) (b) In a neutralization section of a fertilizer production plant intermediate mother liquor flows into and out of a tank. In the tank the pH value of the liquid is controlled by adjusting the inflow of ammonia gas to the tank. The ammonia flow is controlled using a control valve. (D Illustrate the instrumentation diagram ofthis process. (3 marks) (ii) Explain the purpose of the ammonia flow control loop. (1 mark) CONFIDENTIAL CONFIDENTIAL (c) BNQ 30703 Consider the following liquid storage tank shown in Figure Q4(c) with a orosssectional area of 3 ft2. The valve characteristios is given by Fo - grlh. Figure Q4(c) (i) show that the linearized process has a first order characteristics. (5 marks) (ii) (d) Calculate the time constant of the system at an operating level of 9 ft. (l mark) Consider two tanks in series as shown in Figure Q4(d). F, h andA represent the liquid flow rate, height of liquid and cross sectional area of tank respectively. Assume that the flow rate of an effluent sfieam from a tank is proportional to the cubic root of the liquid height. g F n'-. --' [*, -{; -, z6 * I ? /fi 4 t I Vft" a *-|' ..'L7 Figure Q4(d) Establish a Laplace transfer function based model relating input-output variables which is intended to control height of liquid in the second tank. (8 marks) CONFIDENTIAL CONFIDENTIAT (e) BNQ 30703 Figure Q4(e) below shows a ship. The control variable is the position of the ship. Assume that it is beneficial for the positional contnol system that the rotational speed of the propeller is also controlled. Based on the given information" propose the purposes ofthe contol loops forthe ship (3 marks) Rn*rtimnl ssed sF[rH]r R$n$snaf *pecd mafisllsr Figure Q4(e) (f) Given a temperature sensor which represents temperatures, 1', in the range of 15 55oC, with a measupment signal (current), M, rnthe range of 4 - 20 mA, with a linear relation between these ranges. Determine the scaling function with C as input and T as output on the following form: T= alll + b (2 rnarks) 10 CONFIDENTIAL CONFIDENTIAL BNQ 30703 Q5 (a) (i) Define 'acceptable stability' (ii) Define'controller tunning'. (i) Explain the term 'overide controlo. (b) (l mark) (l mark) (2 marks) (ii) (c) Describe whether there any processes for which open loop excitation should not be used. (2 marks) Figure Q5(c) below shows a simple drilling machine. Csntr:ol-cafi {UplOowrd5tcady} Ccntrol*dftll {odCIfn F*sitton p-hlgh ContmLstart tilrd0ff) fu{easured pasitinn h{eas-p C$ntfirl-clantp {OnlOffi Fusttl*n p*lrw Ierc pasltlcn Wo*plece Figure Qs(c) Sketch a Sequential Function Chart (SFC) with steps, actions and transitions solving the control task given above. The operation of the machine is described below. tlv control signal pressed, it pops up has been Control;tart to value On. Just afier the the button (his reset is not a automatically qnd Controlistart is automatically set back to Off part of tlrc control task inthis exercise). When the driUing operationhas been started, the clamps are activated by setting tlrc control signol Control-clamp to On, tlrc drill starts rotating with Control_drill set to On, and the cart is moved dowtwards with Control_cart set to Down until the measured drill position Measl becomes p-low. Then, the cart is automatically moved upwards with Control-cart set to Up. When the Measlt has become p_high, the cart is stopped with Control-cart set to Steady, the clamp is released with Control_clamp set to Off, and the drill is stopped with Control_drill set to Ofi, Then tlp drill is idle, waiting until the Start button is again The drilling operation is started with the Start button which sets pressed. (6 marks) ll CONFIDENTIAL CONFIDENTIAL (d) BNQ 30703 The circuit in Figure Q5(d) below is the basis of a temperature controller. Study the diagram answer the questions below. sin *r{T*.T*} Figure Qs(d) (i) Examine the circuit function and how does it work. (3 marks) (ii) Determine the type of additional circuit needed between the output and the heater. (2 marks) (iii) (iv) Explain why there is a diode in series at the output. (l mark) Summ arize on how you would improve the circuit. (2 marks) (e) Given a controller with analog output (control sigrral) in the range 0 -20 mA. Suppose the controller is to be used to control a device (e.g. a pump) that only takes voltage in the range 0 - l0 V. Convert the current control signal to a corresponding voltage control signal. (3 marks) t2 CONFIDENTIAL " CONFIDENTIAL (0 BNe 30703 Given the following transfer function: rf{s}- e,+3s+2 = "13 ' (i) (iD Determine the order of the above equation. (l mark) (l mark) Propose the characteristic equation. .EI\ID OF QUESTIONS. l3 CONFIDENTIAL "t I CONFIDENTIAL BNQ 30703 FINAL DGMINATION SEMESTER/SESSION COURSE PROGRAMME : 3BNN :PROCESSCONTROL COURSECODE :8NQ30703 :SEMII/20lsnOrc Formula -, 4EH* - fud*+ihJil,ff*{r}*, ffr* ffifS Lrrtt3 4 c*fs#*t ' fr{r} Jf -cr} -,Irwa +=F{c;o rtT E't*)=SP(rl-Cl"(tl a -:_T gS * r st#l . + f strldr-r' -r *ffit = ttl*f*'n' & Fr t I J fr{t}'=EI*i(s} f ZlZi:fI/(t+ IIe) ,dh dEf=Ft-4-lS ,4t*l ndti) ,= .F(*) ts - ry{{l- Ifrft) *sX* +..s) T4 CONFIDENTIAL