A counter is set to some preset number of value and, when this value of input pulses has been received, it will operate its contacts. Thus normally open contacts would be closed, normally closed contacts opened.
There are two types of counter, though PLCs may not include both types. These are down-counters and up-counters. Down-counters count down from the preset value to zero, i.e. events are subtracted from the set value. When the counter reaches the zero value, its contact change state. Most PLCs offer down counting. Up-counters count from zero up to the preset value, i.e. events are added until the number reaches the set value. When the counter reaches the set value, its contact change state.
(Bolton W, Programmable Logic Controllers, Fourth Edition , p.173)
Counter (new) (Better)
There are two basic counter types: count-up and count-down. When the input to a count-up counter goes true the accumulator value will increase by 1 (no matter how long the input is true.) If the accumulator value reaches the preset value the counter DN bit will be set. A count-down counter will decrease the accumulator value until the preset value is reached.
An Allen Bradley count-up (CTU) instruction is shown in Figure 9.15. The instruction requires memory in the PLC to store values and status, in this case is C5:0. The C5: indicates that it is counter memory, and the 0 indicates that it is the first location. The preset value is 4 and the value in the accumulator is 2. If the input A were to go from false to true the value in the accumulator would increase to 3. If A were to go off, then on again the accumulator value would increase to 4, and the DN bit would go on. The count can continue above the preset value. If input B goes true the value in the counter accumulator will become zero.
(Automating Manufacturing Systems with PLC, Hugh Jack, p.179)
2) Encoder (Electronic device)
1. A device that is capable of translating from one method of expression to another method of expression. For example, an encoder might translate a verbal message, "add the contents of A to the contents of B," into a series of binary digits. Contrast with decoder.
2. A device that transforms a linear or rotary displacement into a proportional digi-
tal code.
3. A hardware device that converts analog data into digital representations.
(Paul G. Friedmann,The Automation, Systems, and Instrumentation Dictionary 4th ed. , pg.177)
Encoder (new) (Better)
Encoders use rotating disks with optical windows, as shown in Figure 23.3. The encoder contains an optical disk with fine windows etched into it. Light from emitters passes through the openings in the disk to detectors. As the encoder shaft is rotated, the light beams are broken. The encoder shown here is a quadrature encode, and it will be discussed later.
There are two fundamental types of encoders; absolute and incremental. An absolute encoder will measure the position of the shaft for a single rotation. The same shaft angle will always produce the same reading. The output is normally a binary or grey code number. An incremental (or relative) encoder will output two pulses that can be used to determine displacement. Logic circuits or software is used to determine the direction of rotation, and count pulses to determine the displacement. The velocity can be determined by measuring the time between pulses.
Encoder disks are shown in Figure 23.4. The absolute encoder has two rings, the outer ring is the most significant digit of the encoder, the inner ring is the least significant digit. The relative encoder has two rings, with one ring rotated a few degrees ahead of the other, but otherwise the same. Both rings detect position to a quarter of the disk. To add accuracy to the absolute encoder more rings must be added to the disk, and more emitters and detectors. To add accuracy to the relative encoder we only need to add more windows to the existing two rings. Typical encoders will have from 2 to thousands of windows per ring.
(Automating Manufacturing Systems with PLC, Hugh Jack, p.524)
3)Serial Data Communication (Data transfer)
Modern sensors have a digital front end for transmitting measured parameters. The signal acquired from the external world is packets of digital data and then serially transmitted. This reduces the amount of cabling required to bringin data from various sensors of a robot’s surroundings. A typical sensor along with electronic s could transmit the acquired signals using one of the many Standard physical layers and protocol standards.
(Rahul Dubey,Introduction to Embedded System Design Using Field Programmable Gate Arrays, 1st Edition, pg102)
Serial Data Communication (new) (Better)
Serial communications send a single bit at a time between computers. This only requires a single communication channel, as opposed to 8 channels to send a byte. With only one channel the costs are lower, but the communication rates are slower. The communication channels are often wire based, but they may also be can be optical and radio. Figure 27.2 shows some of the standard electrical connections. RS-232c is the most common standard that is based on a voltage change levels. At the sending computer an input will either be true or false. The line driver will convert a false value in to a Txd voltage between +3V to +15V, true will be between -3V to -15V. A cable connects the Txd and com on the sending computer to the Rxd and com inputs on the receiving computer. The receiver converts the positive and negative voltages back to logic voltage levels in the receiving computer. The cable length is limited to 50 feet to reduce the effects of electrical noise. When RS-232 is used on the factory floor, care is required to reduce the effects of electrical noise - careful grounding and shielded cables are often used.
(Automating Manufacturing Systems with PLC, Hugh Jack, p.628)
4) Component Cost: (Manufacturing Economy)
The components of a product (also simply called parts of the product) may include standart parts purchased from suppliers. Exampes of standart components include motors, switches, electronic chips, and screws. Other components are custom parts, made according to the manufacturer's design from raw materials, such as sheet steel, plastic pellets, or aluminium bars. Some custom components are made in the manufacturer's own plant, while others may be produced by suppliers according to the manufacturer's design specifications.
(S.Kalpakjian, S.R.Schmid,Manufacturing Engineering and Technology,5th editon, pg.214-215)
Component Cost:(new) (Better)
The component cos is the most important part of the cost model. It accounts for the majority of the product cost. Currently, production based on an ‘assamble-to-order’ practiceis prevalent in modular design. Product variants can be generated based on the physical components, which can be bought ‘off the shelf’. Thus, the component cost can be used as a basic costing element. In this way, the lower level product cost information, such as the primitive manufacturing elements (e.g. material, machining, labor, etc.) is not required. By analyzing the h,storical data, cost road mapscan be built for the componenets to indicate the trend of the cost evolution.
The production volume is an important factor that influences the unit cost of a component. A higher production volume usually leads to a lower unit cost because of the possible quantitydiscounts. Moreover, cost usually decreases with time due to the learning effect and technology advancement.
(Design reuse in product development modeling, analysis and optimization, S. K. Ong,Andrew Y. C. Nee, p.171)
5)Operating System: (Computer program)
An operating system is a program that manages the computer hardware. It is also provides a basis for application programs and act as an intermediary between a user of a computer and and the computer hardware. An amazing aspect of operating systems is how varied they are in accomplishing these tasks. Mainframe operating systems are designed primarily to optimize utulization of hardware. Personal Computer (PC) operating systems support complex games, business application, and everything in between. Hand-held computer operating systems are designed to provide an environment in which a user can easily interface with the computer to execute programs. Thus, some operating systems are designed to be convenient, others to be efficient, and some others combination of two.
(S.Kumar, Encyclopaedia of Operatin System, pg.1)
Operating System: (new) (Better)
An operating system - commonly referred as an OS – is a set of computer programs that manage the hardware and software resources of a computer. The Os processes electronic devices with a rational responce to commands that are approved by the system.
At foundation of all system software, an operating system performs basic tasks like controlling and allocating memory, priotizing system requests, controlling input and output devices, faciliating the network, and managing files. The OS can also provide a graphical user interface for higher functions. Essentially, the OS forms a platform for other system software as well as application software.
The operating system is the most important program that runs on a computer. Without an operating system, your computer would not work. It would not be able to process request for print, simple calculations, or any other function. It is really the brain that runs the equipment.
For larger system, the OS has great responsibilities than with a PC. In larger systems, the operating system is kind of like atraffic cop. It makes sure that different users and programs running at the same time on different systems don’t interfere with each other. It also acts as a security guard making sure that unauthorized users are not able to access the system.
(Operating Systems Uncovered, Stephen Lindsay,p.2)
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