Electronic Digital Controllers

Sample rates for the majority of digital controllers are adjustable and range from 1 sample every 5 s to 10 samples per second. Some controller designs have fixed sample rates that fall within the same range. Hardwired low-pass filters are usually installed on the analog inputs to the controller to help protect the sampler from aliasing errors. 

Some digital controller designs allow the execution rates of control strategy elements to be set independently of each other and indepen- 

The PC can also be interfaced to a DCS to perform advanced control or optimization functions that are not available within the standard DCS function library. 

When one is tuning a controller, the form of the PID algorithm must be known. The three common forms of the PID algorithm are parallel 

Differences in the PID algorithm, controller parameters, units, and other fundamental control functions highlight the importance of understanding the structure of the controller and the requirement of sufficiently detailed documentation. This is especially important for the controller but is also important for the field instruments, final control elements, and device tnat have the potential to affect the signal characteristics. 

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Figure 4.21 shows a screenshot from a modem DCS. Simply put, a DCS is an electronic digital control system where computers spread functionality over multiple processes in large-scale plants. The advantage of a DCS is that it allows operators to monitor and control entire plants from a central control room. 

Figure 4.20 Electronic digital controller Fisher DPR series (reproduced by permission of Emerson Process Management)...

Mossbauer spectra are usually recorded in transmission geometry, whereby the sample, representing the absorber, contains the stable Mossbauer isotope, i.e., it is not radioactive. A scheme of a typical spectrometer setup is depicted in Fig. 3.1. The radioactive Mossbauer source is attached to the electro-mechanical velocity transducer, or Mossbauer drive, which is moved in a controlled manner for the modulation of the emitted y-radiation by the Doppler effect. The Mossbauer drive is powered by the electronic drive control unit according to a reference voltage (Fr), provided by the digital function generator. Most Mossbauer spectrometers are operated in constant-acceleration mode, in which the drive velocity is linearly swept up and down, either in a saw-tooth or in a triangular mode. In either case. 

One industrial facility that has done exhaust system retrofit is the Eldec Corporation, an aerospace electronic manufacturer. With the help of the local utility, Eldec implemented a control project to reduce exhaust air by up to 30% for the first shift and 60% for the rest of the time and achieved great savings with one year simple payback. The project closed the exhaust inlets with dampers and controlled the exhaust fan speeds with variable frequency drives (VFD). The exhaust fans are now monitored and controlled by the building direct digital controls (DDC) system to ensure proper operation and save energy. 

Standard domestic microwave oven rated at 700-1000 W, with turntable for constant temperature and electronic digital timer control. 

Fig. 20 Schematic of the electronics module controlling the CWBP. DA -darlington amplifiers, DAC -digital to analog converter, ADC - analog to digital converter, Amp-disc -amplifier discriminator for the photomultiplier (PMT), PS -pulse stretcher, OSC -oscillator, Zero pos - zero position sensor, Top pos -dip probe position sensor, RM - carousel rotary stepper motor, UPM - linear actuator for the dip probe of the carousel, RT - resistance thermistor, TEC -thermoelectric heat exchanger, Tset - set temperature. (Reprinted from Dhadwal et al. [2], with permission of Elsevier)...

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