CH617519A5 - Arrangement in a controller for limiting the controlled variable to a fixed simulated measured value and use of the arrangement - Google Patents

Description

617 519

Claims (3)

PATENT CLAIMS 1. Arrangement in a controller to limit the controlled variable (xl, x2) to a fixed simulated measured value (mlf, wlf) if the measured value (ml, m2) of the controlled variable (xl, x2) exceeds or falls below a possible range due to the controlled system. characterized by a measuring device (Ml, M2) for measuring the controlled variable (xl, x2) and a limiter device with switch (Bl, B2) for determining whether the range is exceeded or not reached and for switching either the measured value (ml) of the controlled variable (xl ) in a controller (Rl) without an integral component or the controller output (wl) in a controller (R2) with an integral component to a fixed predetermined value (mlf or wlf). 2. Arrangement according to claim 1, characterized in that a signaling device is present and the limiter device is connected to the same in order to report an overrange or underrange. 3. Use of the arrangement according to claim 1 in cascade control circuits, characterized in that if the controlled variable measuring device (M1 or M2) fails, emergency control can be carried out by switching on one and the same fixed predetermined value of the associated controlled or manipulated variable. The present invention relates to an arrangement in a controller for limiting the controlled variable to a fixed simulated measured value when the measured value of the controlled variable exceeds or falls below a range that is possible due to the controlled system. If a measuring device for recording the controlled variable fails in a control circuit, the output signal of the defective measuring device is compared with the reference variable. This then leads to extreme values of the manipulated variable. It is the object of the invention to incorporate an arrangement into the control loop with which the disadvantage mentioned above is avoided. According to the invention, this is achieved by the features in the independent patent claim. During operation, a kind of emergency control can be maintained with this arrangement in the case of so-called cascade controllers. An exemplary embodiment of the invention is explained in more detail below with reference to the drawing. A cascade controller circuit is shown in the single figure. As can be seen, a control process is a self-contained signal sequence. The disturbance variables have an external effect on this circular process in some form. The control process can thus be represented in a general form, independently of the details of the technical system, in the form of a block diagram, in which the controlled system is a block 5 with an input variable y (actuator change) and an output variable x (change in the controlled variable). A control device R has the system deviation as the input variable and the variable y as the output variable. In the m drawing, this means: Wl = auxiliary command variable W2 = guide size xl = auxiliary controlled variable 15x2 = controlled variable y = manipulated variable e.g — disturbance variable S1,S2 = first and second controlled system RI, R2 = first and second control device M Ml = Measuring device for the auxiliary controlled variable xl M2 = Measuring device for the controlled variable x2 ml = Measured value of the auxiliary controlled variable xl m2 = Measured value of the controlled variable x2 sheet = Limiter for the measured value ml 25 B2 Limiter for the measured value m2 mlf = fixed measurement wlf = fixed auxiliary command variable This shows the cascade control circuit from the two mi control paths S1 and S2, the control devices R1 and R2, the control variable measuring devices M1 and M2 and the proposed limiter devices B1 and B2. If the measuring device Ml for detecting the auxiliary controlled variable xl is defective during operation and the probable -15 range of ml is exceeded, the limiting device B1 switches to the fixed value mlf and the exceeding of the range can be reported via a signaling device (not shown). The control loop remains fully functional, although the dynamics are poorer. 40 If the measuring device M2 for recording the controlled variable x2 is defective and the probable range of m2 is thus exceeded, the limiter device B2 switches to the fixed command variable wlf in this case because of the integral component of the controller device R2, and the range excess can be detected by means of the 45 signaling device be reported The controlled variable x2 then remains uncontrolled; however, the auxiliary control circuit for the auxiliary controlled variable xl remains fully functional. C 1 sheet of drawings