The programmable controller

Benefits ascribed to the use of PLCs in comparison to the older stand-alone analog controller are 5,)  

The input/output units of the programmable controller constitute the interface between the PLC and the outside world. Hence, they are provided with the necessary signal conditioning functions which enable the PLC to be connected directly to the process actuators and transducers as desired. For this purpose the 

Signal level Description Signal level Description 

5V (usually DC TTL level) Switched1 Typically up to 240V AC or DC Relay output 

24V (usually DC but sometimes AC) Switched Typically up to 240V AC only SSR (solid-state relay or triac) 

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The instruction list of the programmable controller is stored in an EEPROM 3800 instructions, with ... 

In the calculation of the gas consumption, it is assumed that this is regulated by a modem controller of the type installed in the latest gas chromatographs. The programmable control of the split reduces gas consumption by the equipment and hence considerably reduces the cost of the carrier gas (helium). 

Kosmowski K.T., Sliwinski M. 2007. Risk Analysis and probabilistic modelling based on knowledge in designing and operation of the programmable control and protection systems. Gliwice Pomiary Automatyka Kontrola Vol.4 135-138. 

Programmable controllers are specific microcomputers that are designed to replace electromechanical relay logic systems. These instruments can be connected to computers for data logging or the computer may act in a supervisory capacity over the programmable controller. 

Description of a TGA Instrument. The components of the instrument are the microbalance, the furnace, the programmer controller, and a computer or data acquisition system. Topical arrangements of the components for TGA are shown in Figure 13. The sample can be linked to the balance in three different ways (i) above the balance, (2) below the balance, and (3) beside the balance as a horizontal extension to the beam. 

The greatest advantage of this new type of electrode is its ability to function as a stationary and a nonstationary mercury electrode, as well as the possibility of synchronizing the electrode (drop) formation with the programm-control arrangement. The reproducibility of the mercury metering of an SMDE is important for its dependability in operation. In a commercial model (Multi-Mode electrode, Metrohm AG, Switzerland), the mercury is pushed through the capillary by a ni-... 

By analogy with the control loop hierarchy, one can split the control chain into the process to be controlled and the control system, as shown (for example) in Figure 12.18. In the given example, the process consists of the tank, which can be filled, the control valve with the appropriate piping, the restrictor, the level and flow transducers and perhaps a recorder the control system covers the programmable controller, the signal transmission, and the I/P converter. 

The programmable controller carries out its functions in one or more of the following ways ... 

Failure analysis of the programmable controller, therefore, consists of examining ways and means by which it can fail to carry out the above functions. The PC failure modes of interest, thus, are as follows ... 

Analysis of the programmable controller such that the reliability of the device itself could be estimated and a review carried out of its design and... 

The detailed fault tree models provide useful Information about the Impact of various component failures on the overall operation of the programmable controller. However, because of their size and complexity, they are unsuitable for direct Inclusion In the fault tree models of the various process systems. It, therefore, became necessary to develop simplified fault tree models that would, nevertheless, retain the major contributors to system failure. 

It has also enabled a thorough review to be made of the reliability of the programmable controller Itself, as well as of the manner In which the device Is utilized In the realization of process control functions. 

So, from the general comments above, the electromagnetic environment seems to be able to play an important complex role for PES safety. The experimental work now presented deals with the programmable controller with respect to the other subsystems, its EM susceptibility takes most specifically the problem. 

This Standard determines the technical and constructional characteristics together with the tests to be applied to the Programmable Controller (PC) In specified conditions of use. 

ROM organization is given in Fig. 9.19. The ROM circuit is divided into four banks of 16k x 8 bits for a total programme memory of 64 kbytes. This is also the normal addressing space of 8085. Because we also need RAM for data storage, the programme-controlled bank switch was introduced. 

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