Interlock, interlocking control

The NORIT Porta-Powdered Activated Carbon (Porta-PAC) dry injection system pneumatically conveys an adjustable amount of powdered activated carbon (PAC) from bulk bags into the flue gas streams of incinerators for mercury and dioxin emission reductions. PAC is metered using a volumetric feeder into a pneumatic eductor where moving air transfers the carbon to the injection point. A series of interlocks control the operation of the unit and allow local or remote operation and monitoring of the unit. This technology is commercially available. All information is from the vendor and has not been independently verified. 

ATP and ADP concentrations set the rate of electron transfer through the respiratory chain via a series of interlocking controls on respiration, glycolysis, and the citric acid cycle. 

Preliminary interlock,control, 8 instrument wirinq specs. ... 

A safety interlock control function must be separate from the BPCS. Its function is not on-spec product but the prevention of a catastrophic event that would result in human injury or death or damage to equipment. Safety interlocks are usually hardwired to make it difficult to bypass or defeat them. This is done because there have been past occurrences of a unit engineer or a process technician jumping to the conclusion that an alarm was faulty and there was no problem. They tried to go around the interlock to shut off the alarm or prevent process interference. Safety interlocks must not be bypassed without written approval. 

CC Consistency Controller, CT Consistency Transmitter, CV Control Valve DCV Dilution Control Valve, FC Flow Controller, FT Flow Transmitter GM Refiner Gear Motor, 1C Interlock Controller, M Refiner Drive Motor... 

Here we only focus on the interlock control mechanism. So certain components are ignored, such as Alul, Alul, Memadd and Memory. We also assume that the functional operations in each component are correctly implemented. We also ignore the cache loading mechanism, i.e., we assume that the complete instruction tree is already in the Cache. 

A permissive is a special type of interlock that controls a set of conditions that must be satisfied before a piece of equipment can be started. Permissives deal with start-up items, whereas hardwire interlocks deal with shutdown items. A permissive is an interlock controlled by the distributive control system (DCS). This type of interlock will not necessarily shut down the equipment if one or more of its conditions are not met. It will, however, keep the equipment from starting up. 

In a cement works the sequence and interlock control of the numerous motors and associated machinery is of major importance. As distinct from automatic process control, these plant motor control functions are basically performed on the open-loop principle and play an important part in ensuring reliable and economic operation of the production lines. 

Electronic motor (sequence and interlock) control systems have come into widespread use in the cement industry in recent years. The real breakthrough came with the introduction of programmable controllers. The systems now employed are robust, reliable and easy to handle. In contrast with relay technology, there are no moving parts that suffer wear. 

EN ISO 12100 provides guidance on undertaking general risk assessments associated with a machine and, if it is found necessary to provide risk reduction using an active interlock/ control mechanism, the evaluation of both the requirements and design of this interlock/ control mechanism can be undertaken by using either EN ISO 13849 or EN 62061 as illustrated in Figure 9.1. 

A safety interlock is a design safety arrangement whereby the operation of one control or mechanism allows, or prevents, the operation of another function. The safety interlock is a special safety device used in a system design to increase the level of safety of a specific function it is a DSF. The primary purpose of an interlock is to provide a mechanism to make or break an SR function, based upon a set of predetermined safety criteria. It should be noted that interlocks are absolutely not necessary for the operational functionality of a system. An interlock is a device added to the design in order to achieve the needed safety required of the system, not for the operational effectiveness of the system. Interlocks control state transitions in an attempt to prevent the system from entering an unsafe state or to assist in exiting from an unsafe state. 

Figure 7-16 indicates several key control loops (a) The pressure of the core system is controlled from sensed pressure by the proportioning of power to the pressurizer electric heaters the blanket pressure is similarly controlled by a core-to-blanket differential-pressure signal. (b) The liquid levels in the pressurizers are controlled from sensed levels by pneumatic control of the letdown valves. Pneumatic control actions are derived from transducers which receive signals from electric transmitters. Electric interlock control of the pneumatic signals to final control elements is achieved by the use of solenoid-actuated pilot valves. 

This approach leads to the identification of hardware or software improvements that address the specific requirements of the installation under consideration. Software improvements cover such issues as safety management systems, incident response procedures, training, quality, maintenance practices, alarm and trip testing, etc. Hardware improvements cover such issues as ventilation, gas detection, interlocks, control system, fuel system, protection systems, etc. 

The next step is to apply a number of loss control credit factors such as process control (emergency power, cooling, explosion control, emergency shutdown, computer control, inert gas, operating procedures, reactive chemical reviews), material isolation (remote control valves, blowdown, drainage, interlocks) and fire protection (leak detection, buried tanks, fire water supply, sprinkler systems, water curtains, foam, cable protection). The credit factors are combined and appHed to the fire and explosion index value to result in a net index. 

Normal Operation. The designer of a chemical plant must provide an adequate interface between the process and the operating employees. This is usually accompHshed by providing instmments to sense pressures, temperatures, flows, etc, and automatic or remote-operated valves to control the process and utility streams. Alarms and interlock systems provide warnings of process upsets and automatic shutdown for excessive deviations from the desired ranges of control, respectively. Periodic intermption of operations is necessary to ensure that instmments are properly caUbrated and that emergency devices would operate if needed (see Flow measurement Temperaturemeasurement). 

Many of these features are interrelated. Finely divided soHds such as talc [14807-96-6] are excellent barriers to mechanical interlocking and interdiffusion. They also reduce the area of contact over which short-range intermolecular forces can interact. Because compatibiUty of different polymers is the exception rather than the rule, preformed sheets of a different polymer usually prevent interdiffusion and are an effective way of controlling adhesion, provided no new strong interfacial interactions are thereby introduced. Surface tension and thermodynamic work of adhesion are interrelated, as shown in equations 1, 2, and 3, and are a direct consequence of the intermolecular forces that also control adsorption and chemical reactivity. 

In continuous processes, most process control applications rely on continuous measurements. In batch processes, many of the process control applications will utihze discrete as well as continuous measurements. In both types of processes, the safety interlocks and process interlocks rely largely on discrete measurements. 

By attempting to maintain process conditions at or near their design values, the process controls so attempt to prevent abnormal conditions from developing within the process. Although process controls can be viewed as a protective layer, this is really a by-product and not the primaiy func tion. Where the objective of a function is specifically to reduce risk, the implementation is normally not within the process controls. Instead, the implementation is within a separate system specifically provided to reduce risk. This system is generally referred to as the safety interlock system. 

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