We have described a set point as a setting that is entered as a constant value, representing the desired value of the controlled variable.
The system is defined as the combination of hardware and software that is carrying out the manufacturing and control process. Fig. 17.3 shows a block diagram which describes a general closed-loop system. In this case, the resultant control model would be an intermittent (manual) closed-loop control as shown in Fig. 17.2.Ĭlosed-loop controls: While open-loop control systems for heaters are still used in some situations, virtually all molding machines and extruders have utilized closed-loop controllers for barrel temperature control. The technician might also measure the melt directly with a pyrometer, to make the decision on how much to change the voltage level (amount of voltage provided to the heater band). In practice, the actual temperature of the nozzle body might be measured by a separate thermocouple (TC) probe and be monitored by the technician who would make adjustments as necessary, based on his experience. Since there is no feedback loop included, this would be an example of open-loop control as illustrated in Fig. 17.1. The output of the controller is constant at any given setting. For instance, earlier machines often managed nozzle temperature with a variable voltage transformer which provides power to a resistance heater, delivering from 0% to 100% of the available voltage. Open-loop controls: Process control technologies have been incorporated into plastics machinery as they became available to industry. However, neither the speed nor position can be controlled accurately without feedback. Any of these inputs could be used to set the duty cycle of the drive waveform.
Analogue control is possible from a manual input (RV1) or from a remote voltage source.
Alternatively, the speed could be set at the binary inputs to port B, either manually at the DIP switches, or with an 8-bit digital input code supplied from a master controller. The push-button inputs could be programmed to run the motor in either direction, or to increment and decrement the speed in one direction by modifying the delay in a PWM program. Open loop speed control can therefore be implemented by outputting a PWM signal at either RA4 or RA5. They must not be high together this would switch on both transistors, resulting in no current through the motor, and possible damage to the power transistors. In the MOT2 circuit ( Figure 11.3), the motor can be driven in either direction by setting RA4 or RA5 high, with both set low to turn the motor off. Open loop control of a dc motor (MOT1) has been described in Chapter 8 and a program developed which allows the speed to be controlled manually. Martin Bates, in PIC Microcontrollers (Third Edition), 2011 11.3.1 Open Loop Control As for software, the open-loop control is required to carry out the complex positioning control of the motor, and the complexity of the program is relatively high. In terms of hardware, the open-loop control system generally uses a limit switch, with the collocation of a stepper motor, a servomotor, or an encoder motor to achieve the positioning function of the condenser.
At the same time, it is also required that the limit switch is set to achieve the desired reduction of the device. The premise of accurate tracking is to ensure the accurate positioning of the sun tracking device and the algorithm of the sun's motion. The tracking position at any time is determined by the time and space functions of the tracking device. This method is not affected by weather conditions, but the sun's trajectory changes with the location of the tracking device, the latitude, and seasonal variations. When the actual angle of solar concentrator is equal to the target angle, open-loop control is completed.
Calculate angles of the sun through the time and latitude and longitude information, and then calculate the target angle of tracking solar concentrator, and then program control driving solar concentrator from present position to the target angle. The open-loop control method determines the location of the sun by using the location and running time information in the collector. All data are stored in the computer, according to the sun's designated position at the time, to control the motor rotation driven by the tracking device to track the sun. According to astronomical formulas, the sun's azimuth and height angle real-time data can be calculated from sunrise to sunset every day and every year. Open-loop control is the same as sun position tracking. Chang, in Advances in Solar Heating and Cooling, 2016 5.3.3 Principle of open-loop control