Microprocessor-based control

As microprocessor-based controls displaced hardwired electronic and pneumatic controls, the impac t on plant safety has definitely been positive. When automated procedures replace manual procedures for routine operations, the probability of human errors leading to hazardous situations is lowered. The enhanced capability for presenting information to the process operators in a timely manner and in the most meaningful form increases the operator s awareness of the current conditions in the process. Process operators are expected to exercise due diligence in the supervision of the process, and timely recognition of an abnormal situation reduces the likelihood that the situation will progress to the hazardous state. Figure 8-88 depicts the layers of safety protection in a typical chemical jdant. 

With this technology it is now possible to achieve extremely accurate speed control of the order of 0.01 % to 0.001 %. To achieve such high accuracy in speed control, closed-loop feedback control systems and microprocessor-based control logistics can be introduced into the inverter control scheme to sense, monitor and control the variable parameters of the motor to very precise limits. 

Moderate to precise controls as for a.c. drives possible with the use of microprocessor-based control systems... 

All control scheirres shown with auxiliary contactors and timers can be easily replaced with PLCs and microprocessor-based controls. Refer to Section 13.2.3 for mote details. 

Digital control A control loop in which a microprocessor-based controller directly controls equipment by means of sensors. Its operation depends on a series of on-off pulses arranged to convey information. 

Microprocessor-based control systems are being increasingly used in place of traditional instrumentation. Some accidents that have occurred on these systems are described in Chapter 20. 

Manufacturers now offer as standard microprocessor-based control systems as part of their gas turbine generator set. The set can therefore be controlled and monitored from panels adjacent to the machine or, if required, remotely from a central control room. In combined-cycle installations, the system would be linked into the... 

Multistep batch processes are amenable to microprocessor-based control systems. Porte et al. (1982) have shown that the seven-step process for making (1-ethyl-2-pyrrolidinyl) (2-... 

All controllers, be they 30-year-old pneumatic controllers or modern distributed microprocessor-based controllers, have these features. 

The sterilization process is controlled by the microprocessor-based control system. Temperatures and pressures are measured from the chamber... 

Microprocessor-based control systems are marketed under a variety of acronyms and not all will be true DCCSs. Of particular note are the Supervisory Control and Data Acquisition (SCADA) systems which form an increasingly central part of the operations of many industries (e.g. offshore oil and gas platforms, petrochemical complexes, pulp and paper works). SCADA describes a communications system whose principal function is to join instrumentation and control into a cohesive package(57) and, particularly, the supervision and management of remote ... 

Electronic modules are the industry standard for controllers employing a wide range of control strategies. Although, more recently, there has been rapid development of microprocessor-based controllers (see Sections 7.20 and 7.21) where control actions are simulated using software, hard wired systems based upon the integrated circuit (IQ and operational amplifier (op-amp) are still much in evidence. 

IDEX Corporation. PULSAtrol Microprocessor Based Controllers and Monitors Reference Guide. Promotional literature, Pulsafeeder IDEX Corp., USA. 

HPLC systems operate on a master-slave arrangement in setting up for automation. One module sets the timing and initiates the process, and the remaining modules accept a signal and follow the leader. In a gradient HPLC system, the master module can be a microprocessor-based controller, a computer software-based controller, an autosampler, or an integrator. 

Since the 1970s, process controls have evolved from pneumatic analog technology to electronic analog technology to microprocessor-based controls. Electronic and pneumatic controllers have now virtually disappeared from process control systems, which are dominated by programmable electronic systems based on microprocessor technology. 

The first two approaches appear to be the most suitable for chemical process applications the robust controller is particularly attractive for microprocessor-based control. The second... 

Recently all of the temperature, pressure, and time controls have been replaced with a single microprocessor-based controller. A number of these are available and they allow for complex pressure and temperature curves to be programmed with multiple soaking levels and variables that can be chosen. Built-in memories recall previous programs and cassettes can store them on the shelf. Interfaces can connect with a central host computer for data collection or actual machine setup and supervision. The result is more flexible, more exacting, and easier to control modern molding equipment (Chapter 3). 

The lamps are covered with a high U V transparent barrier to protect the lamps and lamp intensities are monitored with a variable height control sensor of custom design. Lamp intensity is maintained constant by a microprocessor-based controller and a photodiode sensor to provide a fully automated closed-loop control system. LUWA also makes custom, large-scale units. 

By employing a single, off-the-shelf, microprocessor-based controller that incorporates a second algorithm (representing the control criteria for the entire process), control is much simpler, and more versatile, accurate and reliable, than conventional, auto/manual, single-loop BID (proportional-integral-derivative) controllers and the accompanying process hardware. 

Microprocessor-based control strategies like this one generally include a selectable temperature-setpoint profile that is based on product grade. In other words, the operator can push a button or select from the keyboard the desired temperature profile. A setpoint-generator algorithm then continuously calculates the setpoint as a function of time and feeds it to the controller. The controller, then, controls to this setpoint. 

All these operations take place in a single reactor instead of two as in the conventional AS process (Figure 15). These operations have been made simple by the advent of reliable and inexpensive microprocessor-based controllers. The process has been found to be very efficient in the treatment of a variety of wastewaters. 

The Camag AMD system consists of two main components the AMD developing unit (Fig. Ic) and the microprocessor-based controller. This system provides an AMD under reproducible conditions. For the AMD microprocessor-based controller, the following parameters may be chosen the eluent composition, by selecting the number of solvent reservoir the number of developing steps the developing time for each step the number of preconditions the option of emptying the mixer after a selected step. 

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