Hard-wiring

Atom types represen t the chemical environment of an atom. The atom types associated with a given force field could be hard-wired to have specific vahiesand meaning. llyperChem also allows flexible definitions of the atom types and the associated chemical en vironmen Is. Th e ch em ical en viron men t of an atom (a set of rules for defining a type) and the default rules are in a standard ASCII text file, chem.nil. included with llyperChem. You can modify this file and compile it m a binary form that llyperChem... 

Hard wired. A preprocessor that is capable of performing only certain defined tasks and no others without major physical modification. 

Electronic Connectors. The complexity and size of many electronic systems necessitate constmction from relatively small building blocks which ate then assembled with connectors. An electronic connector is a separable electrical connector used in telecommunications apparatus, computers, and in signal transmission and current transmission <5 A. Separable connectors ate favored over permanent or hard-wired connections because the former facilitate the manufacture of electronic systems also, connectors permit assemblies to be easily demounted and reconnected when inspection, replacement, or addition of new parts is called for. 

Being excellent at discrete logic, PLCs are a potential candidate for implementing interlocks. Process interlocks are clearlv acceptable for implementation within a PLC. Implementation of safety interlocks in programmable electronic systems (such as a PLC) is not universally accepted. Many organizations continue to require that all safety interlocks be hard-wired, but implementing safety interlocks in a PLC that is dedicated to safety functions is accepted by some as being equivalent to the hard-wired approach. 

The resolution of the analog I/O channels of the controller vaiy somewhat, with 12-bit and 14-bit conversions quite common. Sample rates for the majority of the constant sample rate controllers range from I to 10 samples/second. Hard-wired single-pole, low-pass filters are installed on the analog inputs to the controller to protect the sampler from aliasing errors. 

The difference in the nature of process controls and safety interlock systems leads to the conclusion that these two should be physically separated (see Fig. 8-89). That is, safety interlocks should not be piggy-backed onto a process-control system. Instead, the safety interlocks should be provided by equipment, either hard-wired or programmable, that is dedicated to the safety functions. As the process controls become more complex, faults are more likely. Separation means that faults within the process controls have no consequences in the safety interlock system. 

Although the traditional point of reference for safety interlock systems is a hard-wired implementation, a programmed implementation is an alternative. The potential for latent defects in software implementation is a definite concern. Another concern is that solid-state components are not guaranteed to fail to the safe state. The former is addressed by extensive testing the latter is addressed by manufacturer-supplied and/or user-supplied diagnostics that are routinely executed by the processor within the safety interlock system. Although issues must be addressed in programmable implementations, the hard-wired implementations are not perfect either. 

The potential that the logic within the interlock could contain a defect or bug is a strong incentive to keep it simple. Within process plants, most interlocks are implemented with discrete logic, which means either hard-wired elec tromechauical devices or programmable logic controllers. 

Diversity can be used to further advantage in redundant configurations. Where redundant measurement devices are required, different technology can be used for each. Where redundant logic is required, one can be programmed and one hard-wired. 

In the event of fire within a building, the controller for each elevator should isolate all manually operated inputs and return automatically to the evacuation level, usually the ground floor. An output from the building fire alarm panel is hard wired to the elevator controller, giving the signal for a fire condition. The elevator remains disabled at the evacuation level and the car doors open. If a fire officer requires control of a elevator a key switch or break-glass unit should be used to re-activate the elevator. 

For potential surveys on offshore platforms it is necessary to locate numerous reference electrodes at all levels on the structure. The hard-wire connections from these electrodes together with, for example, similar connections from specially monitored sacrificial anodes are best terminated and displayed at the surface on mimic display monitoring panels. 

Moreover, behaviors frequently arise that appear to involve some form of intelligent division of red and blue forces to deal with local firestorms and skirmishes, particularly those forces whose personalities have been evolved (via a genetic algorithm sec below) to perform a specific mission, It is important to point out that such behaviors are not hard-wired but rather an emergent property of a decentralized and nonlinear local dynamics, A small sampling of behaviors is shown below. 

The Pc header includes the seven-bit address (ag-o) of the chip. Four of these bits as-a2, can be hard-wired during bonding. Internal pull-downs set the default values for these bits to 0. 

In addition to the basic control loops, all processes have instrumentation that (1) sounds alarms to alert the operator to any abnormal or unsafe condition, and (2) shuts down the process if unsafe conditions are detected or equipment fails. For example, if a compressor motor overloads and the electrical control system on the motor shuts down the motor, the rest of the process will usually have to be shut down immediately. This type of instrumentation is called an interlock. It either shuts a control valve completely or drives the control valve wide open. Other examples of conditions that can interlock a process down include failure of a feed or reflux pump, detection of high pressure or temperature in a vessel, and indication of high or low liquid level in a tank or column base. Interlocks are usually achieved by pressure, mechanical, or electrical switches. They can be included in the computer software in a computer control system, but they are usually hard-wired for reliability and redundancy. 

First, computer circuits are hard-wired at the factory. A computer s circuitry never changes. In contrast, as we noted previously, brain circuitry is constantly adapting through a process of pruning and reestablishing connections. This pruning affords the nervous system a plasticity that enables it to adapt continually to the demands of an ever-changing environment. 

Installation type Temporary, often mobile setup Permanent, hard-wired and integrated... 

Ainslie s theory of discounting can be conceived as a two-tier theory, consisting of hard-wired hyperbolic discount curves and a cognitive element, namely willpower, in the form of personal rules. 

Fig. 14. Contrast of (left) hard-wire aircraft communicaiions and controls and (right) use of fiber optics. (After United Technologies Research Center)...

One important application of pneumatic transmission is in the operation of diaphragm actuators. These are the elements generally employed to drive the spindles of control valves (Section 7.22.3) and, if hard-wired transmission systems are employed, require devices which convert electric current into air pressure or air flowrate, i.e. electropneumatic (E/P) converters. The basic construction of a typical E/P converter is illustrated in Fig. 6.77. A coil is suspended in a magnetic field in such a way that when a current is passed through the coil it rotates. This rotation is sensed by a flapper/nozzle system (Section 7.22.1). The nozzle is supplied with air via a restrictor and its back pressure actuates a pneumatic relay. The output from the latter is applied to the feedback bellows and also acts as output from the E/P converter. Electropneumatic valve positioners employ the same principle of operation. 

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. 

---