Hardwiring

Fig. 3. Hardwired system having a PLC backup with lockout where the reset button must be pushed once the switch trips. CR = contact relay and LSHH = level switch high-high alarm "or" and "and" gates are designated as boxes.

Cascade control strategies are among the most popular and usehil process control strategies. Modem control systems have made thek implementation and operation both easier from the standpoint of operations personnel, and cost effective as they are implemented in software rather than hardwiring the connections. 

Programmable Logic Controllers The programmable logic controller (PLC) originated as a solid-state replacement for the hardwired relay control panel and was first used in the automotive indus-tiy for discrete manufacturing control. Today, PLCs are used to implement Boolean logic functions, timers, counters, and some math functions and PID control. PLCs are often used with on/off process control valves. 

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. 

The purpose of the logic within the safety interlock system is veiy different from the logic within the process controls. Fortunately, the logic within the safety interlock system is normally much simpler than the logic within the process controls. This simplicity means that a hardwired implementation of the safety interlock system is usually an option. Should a programmable implementation be chosen, this simplicity means that latent defects in the software are less likely to be present. Most safety systems only have to do simple things, but they must do them very, very well. 

Install separate (independent) hardwired safety systems... 

Using the influence coefficient technique for multiplane balancing is simply an extension of the logic, which is hardwired into the standard balancing machine. This extension has been made possible by the availability of better electronics and easier access to computers. 

Process control and safety shutdowns must be provided during all modes of operation, not only in the RUN mode. Other modes will require a BPCS configured for the mode operating algorithm and very likely a different set of safety interlocks must provide appropriate protection. Hardwire devices, like timers or software logic, can be used to actuate the SIS pertinent to the operating mode. 

The view is therefore growing that we should try to design plants so that they are safe even if there is a fault in the software. This can be done by adding on independent safety systems, such as relief valves and hardwired trips and interlocks, or by designing inherently safer plants that remove the hazards instead of controlling them (see Chapter 21). 

Sections 9.1.6 (c) and 9.2.1 (h) drew attention to the hazards of using old equipment. Similar remarks apply to old software except that, unfortunately, it never wears out. I do not know of any incidents in the process industries due to this cause, but it was responsible for the loss of the European space rocket Ariane 5. A function that no longer served any purpose was left in for commonality reasons, and the decision to do so was not analyzed or fully understood [14]. In another incident, cancer patients received excessive doses of radiation because operators were able to enter data faster than the computer could process them. This had always been the case, but originally a hardwired interlock had prevented... 

The high-high probe is completely independent of the other probes and is hardwired to shut down the system completely, independent of the computer. (In the preliminary safety review, the hazards associated with HF overfeed were identified as important thus the independent high-high shutdown probe system was installed.) All systems are designed to fail into safe conditions. The HF control valves are air operated and of a design that makes it impossible for HF to contaminate the air supply. 

The ARC is controlled by its own hardwired control module. The temperature is monitored by a set of seven thermocouples connected in series which measure the difference between the temperature of the sample and that of its surroundings. The temperature is maintained by heaters which receive their inputs from the control module. A pressure transducer is attached to the sample container, giving both an analog readout on a pressure gauge and a digital readout on the control module panel. It should be noted that pressure is monitored but it is not part of the control loop. 

Why bother with all the neurobiology of the human brain, when trying to understand stress Because the old dogma that our brain remains a stable, unchanging, hardwired black box has to be revised. 

Manned control rooms should always be provided with hardwired ESD activation points located on the main control console easily accessible to the operators. 

The hardwired ESD activation means is usually a push in knob or button. Confirmed action of the push button should be always be required to manually activate the ESD system in order to prevent accidental activations. Most commonly a protective cover is fitted over any of the push button or manual activation devices. All devices should only be manually resettable. 

In the initial stages utilities ran wires, also known as hardwire or land lines, from the central computer (MTU) to the remote computers (RTUs). Since remote locations can be located hundreds of miles from the central location, utilities began to use public phone lines and modems, leased telephone company lines, and radio and microwave communication. More recently, they have also begun to use satellite links, the Internet, and newly developed wireless technologies. 

Telephone number(s) (hardwire, cell phones, faxes, e-mail)... 

Once a sensor in an alarm system detects an event, it must communicate an alarm signal. The two basic types of alarm communication systems are hardwired and wireless. Hardwired systems rely on wire that is run from the control panel to each of the detection devices and annunciators. Wireless systems transmit signals from a transmitter to a receiver through the air—primarily using radio or other waves. Hardwired... 

Computer clusters contain a number of processors put together on a motherboard into a unit known as a node. The nodes are then hooked together with other boards via high-speed communications networks. Nodes can be hardwired into supercomputers produced by companies like IBM and Compaq or... 

While the protocol described above has proven very useful in its own right, it often serves as the first step in designing custom protocols for a team. Once a user is satisfied with the results returned by the ad hoc query, the next step is often to hardwire these queries into a protocol that provides one-button access to all the pertinent data for a project. Figure 5 shows such a protocol used to retrieve data for several assays in a Neuroscience project. This protocol highlights an additional filtering option that we make use of in many of our protocols. The text box ( selected cmpds from list ) (7) supports the input of a list of identification numbers (in our case either jnjnumber or batchid ). This allows data to be retrieved on select compounds as opposed to all those tested in the assays. This feature is very popular and involves the use of Perl within the Pipeline Pilot protocol. All this work is done on the server and the results are written to a SD file that can be downloaded to the desktop. At this stage either DIVA or Accord for Excel is typically used to view the files. 

Vilayanur S. Ramachandran has suggested that some laws of aesthetics have been hardwired into the visual areas of our brains to defeat camouflage and discover hidden objects. According to Ramachandran, universal laws of aesthetics cut across not only cultural boundaries, but species boundaries as well. For example, we find peacocks and giant... 

One of the major themes of this book jelled as I toured the cliff-side town of Positano on the Amalfi coast near Naples, where buildings grow like barnacles—from the tops of hills and down the sheer slope to the Gulf of Salerno. It suddenly hit me that behind every society was a hidden, elflike voice that whispered Build Create Build Create Moreover, some of the intricate structures I had seen during my journey were reminiscent of the sparkling, ornate palaces revealed to people under the influence of the psychoactive compound DMT (dimethyltryptamine). It seems as if DMT frees the mind to see the blueprint—hardwired by the whispering elves—instructing us to create, create, create. 

Why do many students shun math-related studies Is it because their minds are not hardwired to do math easily Or is it because the math they ve encountered is not applied to interesting concepts. Is it a bit of both What might be done to help these students overcome their fear of math ... 

An important feature of the distributed control system chosen is that the PCMs can communicate over a microwave link, thus allowing the well pad manifold modules to be included in the GC control system the hardwire data highway is limited to a distance of 5000 ft. (1524m) from the Host. The well chokes and manifold controls will remain on the SCAOA system, but the well pad will require continuous process control of the test separator, water injection flow control, and artificial lift gas flow control. 

The DCS also realizes similar advantages in regards to the GCs, i.e. the reduction in the number of personnel required, reduction in installation costs over conventional hardwired centralized systems, and expansion flexibility. 

Provision of system hardware, software, and associated instrumentation that are part of the contracted supply Application software development, including development testing System assembly Hardwiring of components Documentation preparation... 

Color constancy algorithms can be derived by looking at the underlying physics of color image formation. An interesting question is whether color constancy algorithms are an acquired capability of the visual system, i.e. if they are learnt, or whether these algorithms are hardwired, i.e. evolved. 

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