C3 – 1 Solution 3
Title Closed control loop synthesis and planning of binary control systems
Solution to part exercise 3-1 Investigate the method of operation of the filling level control loop (closed control loop in manual operation; type of action of sensors and actuators). Develop a strategy for computer-aided measured value acquisition. Determine the static characteristic curve of the ultrasonic sensor, i.e. the correlation between filling level and the respective current or voltage signal. Note: Record a sufficient number of interpolation points. Investigation of the experimental areas Regarding communication between computer and process The first step of the experimental analysis, is the investigation of the available technical resources. These comprise the sensors and actuators of the process to be examined and the auxiliary hardware and software equipment required for data acquisition and evaluation. In the case of computer assisted data acquisition, the communication between the process and computer is effected via PC cards or via a bus system (e. g. PROFIBUS). Here, it should be taken into account that the majority of PC cards can only read an output of 0 to 10 V as analogue signals, which necessitates a signal conversion. The analogue ultrasonic sensor used in this system supplies a current signal of 6 to 20 mA analogue to the measured distance. This can be converted into a voltage signal via a load resistance. From the description of the sensor it can be seen, that the load resistance RL must be less than 400 Ω. For instance, if RL = 390Ω is selected, this creates a voltage signal of 2.34 to 7.80 V, which can then be recorded via a PC-card (fig. C3-1a).
Festo Didactic • Process Control System