Typical Open Loop Responses

The process gain, Kp, of the system is the value that the response will go to at steady state after a unit step change in the input, i.e. it relates the input to the output at steady state. 

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In the following text, important aspects in the study of process dynamics are outlined. An example of a dynamic process is given first. Stability of a process is defined next, followed by a discussion of typical uncontrolled, or open loop, responses. 

Figure 4 Typical open-loop unit step responses, (a) First order, (b) Second (or higher)...

A computer simulation of a process with a dead time, DT, of 2 min and a first-order capacitance lag, 7, of 22 min gave an open-loop response shown in Figure 10.2. This was compared with an open-loop response with DT = 2, 7 = 20, and 7 = 2 min. Adding the second capacitance lag, 7, caused the process variable response to be rounded a little after the dead time, which is typical of a plant process response. 

Sampling period and model horizon N. The sampling period Ar and model horizon N (in Eq. 20-6) should be chosen so that N t = tg where tg is the settling time for the open-loop response. This choice ensures that the model reflects the full effect of a change in an input variable over the time required to reach steady state. Typically, 30 A < 120. If the output variables respond on different time scales, a different value of N can be used for each output, as noted earher. Also, different model horizons can be used for the MVs and DVs, as illustrated in Eq. 20-33. 

A typical response for an operational amplifier is given in Figure 6.1(b). The output potential Vb must have a value between Vg+ and Vs-. For an ideal operational amplifier, the open-loop gain Aop is very large (ideally infinite), such that... 

Figures D.3 and D.6 show the responses of frequency in the first one second. Both machines respond in much the same way in the first half second. This is dne to the fact that this part of the response is open loop and is mainly determined by the mechanical inertia and the size of the disturbance, as discussed in Chapter 21 of Reference 1 see also snb-section 2.5 herein. Also shown in these two figures are typical setting levels for underfrequency (81) multi-stage relays. In addition to the setting levels the relays shonld also have time delay settings, so that coordination with other power system equipment can be achieved, e.g. automatic voltage regulators of generators, automatic re-acceleration of induction motors, see also sub-section 7.6 herein. For the settings shown the relays would respond in the range of about 70 to 150 milliseconds, which is typically about half the response...

A related approach to estimating the time delay is to determine the impulse response coefficients, h, for the model. Similar to the cross-correlation plot, the first nonzero value would be assumed to be equal to the time delay. A typical impulse response plot is shown in Fig. 6.5 (right). In this plot, the time delay would be estimated as being four, since that is the last nonzero value before the significant peak. This method requires that the data be obtained from an open-loop experiment. 

Sensor 1 In multiple-loop SNPP ardiitectures with 2 or more Brayton machines, valves are used to direct coolant flow appropriately. Sensing of valve position is necessary for monitoring and control of these valves. For each valve a discrete fixed position sensor is required to be active (asserted) when the valve is in its OPEN position. Othenvise it is inactive (deasserted). Photo, proximity, and microswitch technologies are typically applied as discrete position sensors. /Vocuracy and resolution values for the sensor of 0.1% of point and 0.01 % of point and a response of 0.001 seconds are typical of these tedinologies... 

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