Unformatted text preview: EXAM #1 review CHE 461 Spring 2010 Remember.... Exam #1 is 10 - 11:50 am Fri. Apr. 16, 2010 .. open SEM2 text, Handouts, class notes
and your own HWs. NEW TOPICS - exam may depend upon previous topics (CHE 361) as well as new ones!
Chaps 8,9,11( block diagrams through 11.3, but not 11.4, 11.5 yet) + KLL handouts/notes
Simple analysis of control problems with specified controller Gc(s), Gp(s),Gd(s) and "other" transfer
functions, for example a valve transfer function or a transfer function for an I/P
transducer. For this you must understand transfer functions in parallel and in series.
Offset and PID-type controller performance: effects of Kc, τI and τD values on controller performance.
Servo versus regulatory performance: value of controller output p'(t) = process input u'(t) required to get
an observed process output y'(t) response.
Devices in control loops: sensors/transducers including I/P transducer, control valve selection, sizing,
installed characteristics. TYPES OF PROBLEMS:
You must be familiar with common technical terms and be able to answer quantitative questions, not just
provide qualitative relationships!
1) Identify type of transfer function from step response data; be able to estimate quantitatively the
parameters of simple transfer functions.
- standard form or factored forms of G(s)
- specification of location of poles and zeros along with gain
- given values of standard parameters ( K, θ, τ = 1st or 2nd, ζ and τz )
- step response data or frequency response data 2) Derive a transfer function model from mass\energy balance(s) for a simple process. 3) Be familiar with feedback control nomenclature.
Derive the closed-loop transfer function between the setpoint Y'sp(s), or disturbance D'(s) and the
controlled output Y'(s) in a standard 3-block diagram or other slightly more complex feedback
block diagrams. Identify a setpoint = "servo" problem versus a disturbance rejection or
"regulatory control" problem objective from a description of control objectives. Solve for time
functions of any variable in the block diagram given a step change in the setpoint or disturbance. 4) Be able to translate process flowsheet or written description of relationships into a block diagram
assuming linear dynamic behavior, including aspects of A-O, (ATO, fail-closed) or A-C, (ATC,
fail-open) control valves. 5) Determine the appropriate sign of the controller gain magnitude and other terminology used to
describe process control equipment. Be able to properly present and apply standard time domain
"rule-of-thumb" descriptions of the effects of P, I, and D "actions" on closed-loop performance.
Be able to identify time response effects of controller changes which follow one of the rules of
thumb by examining plots of process input = controller output or process output. 6) Be familiar with MATLAB\Simulink simulation procedures and control loops and be able to
analyze the results which are obtained using the SIMULINK numerical methods to solve ODEs. One more example – from SEM1 textbook (see also Figure 11.7 pg 263 of SEM2) : Temperature transmitter relationships
For T = 10 o C, then Tm = 4 mA
and for T = 50 o C, then Tm = 20 mA
⎡ 20 − 4 mA ⎤
so Tm (mA) = ⎢
⎥ (T − 10 C ) + 4
⎣ 50 − 10 C ⎦
⎛ mA ⎞
Tm (mA) = 0.4 ⎜ o ⎟ T ( o C )
Design/nominal steady state to heat stream by 10 o C
T = Tsp = TR = 30 o C
Ti = 20 o C
Tm = 12 mA
p = 12 mA = controller "bias"
pt = 9 psig "instrument air" ...
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- Winter '08