Closed loop gain

The response time is equal to the ZC product, where Cis the diode capacitance, or when using an integrating amplifier, the response time is determined by the closed loop gain. 

The speed of the controller is adjusted by the proportional band and reset rate (proportional and integral gains). These parameters also influence the stability of the control loop. All control loops are limited to a gain of less than one at their critical frequency. Higher closed-loop gain will make the loop unstable. 

The current-mode controlled forward converter has one additional consideration there is a double pole at one-half the operating switching frequency. The compensation bandwidth normally does not go this high, but it may cause problems if the closed-loop gain is not sufficiently low enough to attenuate its effects. Its influence on the control-to-output characteristic can be seen in Figure B-14. 

The closed-loop gain at dc should be as high as possible. This has a direct bearing on the output load regulation of the supply. 

The resulting average slope of the closed-loop gain curve should be an average of -20dB/decade. 

Next find the closed-loop gain cross-over frequency by deciding how much phase margin you desire in your system. A good value is 45 degrees. Ignoring any effect of the Q of the T-C filter, the gain cross-over point is found from... 

Next, the maximum closed-loop gain cross-over frequency (/(o) is determined and is, once again, no more than one-fifth the minimum switching of the switching power supply ... 

Requires K12K21 = 0. Open-loop gain is the same as the closed-loop gain. The controlled variable (or loop) / is not subject to interaction from other manipulated variables (or other loops). Of course, we know nothing about whether other manipulated variables may interact and affect other controlled variables. Nevertheless, pairing the i-th controlled variable to they-th manipulated variable is desirable. 

We can infer using (10-36) that the open-loop and closed-loop gains have different signs or opposing effects. The overall influence of the... 

Find the closed-loop gain graphically Draw the damping and natural frequency lines... 

MATLAB will wait for us to click on a point (the chosen closed-loop pole) in the root locus plot and then returns the closed-loop gain (ck) and the corresponding closed-loop poles (cpole). MATLAB does the calculation with the root locus magnitude rule, which is explained on our Web Support. 

Once a root locus plot is generated, we can interactively change the locations of the closed-loop poles and the tool will compute the closed-loop gain K for us. 

For a given system and closed-loop gain displayed in the root locus plot, we can generate its corresponding time response (step and impulse) and frequency response (Bode, Nyquist, and Nichols) plots. 

The plot with default settings is quite useless unless we use ngrid to superimpose the closed-loop gain and phase grid lines. Instead of zooming in, we can reset the axes with ... 

In this section we will use PSpice to determine the bandwidth of an op-amp circuit with varying amounts of negative feedback. For an op-amp circuit, the closed-loop gain times the bandwidth is approximately constant. To observe this property, we will run a simulation that creates a Bode plot for several different closed-loop gains. We will use the circuit below ... 

Closed loop gain and measures of gain during masking conditions IV 0.1 mg/kg/1 min 12 4 closed loop gain, eye acceleration and mean mask gain predictive pursuit in response. Weiler et al. (2000)... 

The quantity Rq/ a is called the closed-loop gain. The requirement for operation within the linear regime for the inverting amplifier is that... 

The closed-loop gain A" is the gain in the i-j loop when all the other loops are closed, that is, their controlled variables are held at their set points ... 

The relative gains are defined as the ratios of the open-loop to closed-loop gains ... 

The relative gains may be evaluated from open-loop gains obtained from a steady-state simulator, and from derived closed-loop gains. To determine the open-loop gains from the simulator, the manipulated variables are perturbed one at a time, and the variation in each controlled variable is recorded. If a manipulated variable Mj is perturbed by AMj, resulting in a variation AQ in controlled variable Cj, the gain is approximated as... 

The closed-loop gains can be derived mathematically from the open-loop gains. For a two by two process, the variations AC, and ACj resulting from changes in both manipulated variables are given by the equations... 

The other closed-loop gains may be obtained in a similar manner, and the relative gains follow from their definition by Equation 16.4 ... 

Final elements must provide the desired capacity with the required precision of flow throttling over the desired range, usually 10% to 95% of maximum flow. The valve characteristic should provide a linear closed-loop gain, except choose linear or quick-opening characteristics for valves that are normally closed but must open quickly. Select the valve failure position for safety. The valve body should satisfy such requirements as required flow at 0% stem position, plugging, pressure drop, or flashing. The nonideal final element behavior, such as friction and deadband, should be small, as required by each application. Control valves should have manual bypass and block valves to allow temporary valve maintenance when short process interruptions are not acceptable. However, the bypass should never compromise safety interlock systems. 

Therefore, the ratio of the output to the input, that is, the transfer function of the cascaded G and H blocks, is equal to GH — which is simply the open-loop gain. Therefore, even with the loop closed, as we go around, we are always going to get the open-loop gain GH. Note that the phrase closed-loop gain actually refers to the change in the output, if we change... 

IV.35 A first-order process is controlled with a PI controller. Find the values of the controller gain Kc and reset time t/ so that (a) the closed-loop gain to load changes is 10 and (b) the decay ratio of the closed-loop response is 1/4. The following information is given ... 

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