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外文翻译--PLC简介.doc
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外文翻译--PLC简介.doc
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外文翻译
PLC introduction
PLC is mainly index word arithmetic operations electrical system programmable
logic controller, used to control the production process of mechanical. But a public
limited company, the name of the power supply cord vehicles abbreviation. 1 the
basic concept, the PLC
Early Programmable Controller called Programmable Logic Controller (PLC
Programmable Controller, questions), it is mainly used to replace relay realize Logic
control. With the development of technology, this kind of using microcomputer
technology, industrial control device functionality is greatly exceed the logic control
the scope, therefore, today this device called the programmable controller, or PC. But
in order to avoid Personal Computer (Personal Computer), so will the abbreviation of
confusion as PLC programmable controller, since 1966 PLC us data equipment
company (DEC), and the current U.S. research appears, Japan, Germany's
programmable controller quality is fine, the function is strong.
1, the basic structure of PLC
PLC is essentially a special in industrial control computer, its hardware structure
with microcomputer is same, basically, basic structure for:
A, power
PLC in the system of power plays a very important role. If have no a good and
reliable power supply system is not work properly, so the manufacturers of the power
of PLC design and manufacturing has paid much attention to. In general ac voltage
fluctuation + 10% (+ 15%) range, can not take other measures and will PLC is
connected directly to the exchange network up
B. the central processing unit (CPU)
The central processing unit (CPU) is the PLC control central. It according to the
function of PLC system program gives receives and storage from programmer type of
user programs and data; Check the power, storage, I/O and cordoned-off timer state,
and can the syntax error diagnosis user programs. When PLC is put into operation, it
first to scan all the way of receiving site condition and data input device, and
separately deposited in the I/O image area, and then from the user program memory
read the user program, through detailed explanation according to instructions
commands after regulations logic or count operation results into the I/O image area or
data register inside. All the user program execution after completion, the I/O image of
each output state or output registers transfer data to the corresponding within the
output device, so circulates run, until it stops running.
In order to further improve the reliability of PLC in recent years, for large PLC also
adopt double CPU constitute a redundant system, or adopt three CPU voting type
system. So, even if a CPU malfunction, the whole system can still normal operation.
C, memory
Storage system software of memory called system program memory.
Storage application software of memory called the user program memory.
D, input/output interface circuit
1, field input interface circuit by optical coupling circuit and the input interface
circuit, microcomputer PLC and on-the-spot control function is the UI input.
2, field output interface circuit output data registers, chosen by electricity road
and interrupt request circuit integration, the function of PLC output interface circuit
through the site to site perform component of output corresponding control signals.
E, function module
Such as counting, positioning, and other function modules.
F, communication module
As Ethernet, RS485, profibus-dp communication module, etc.
2, PLC principle of work
A, scanning technology
When PLC investment after the operation, its working process generally divided
into three stages, namely input sampling, the user program execution and output
refresh three stages. Complete the above three stages as a scan cycle. In the whole
operation period, PLC CPU with certain scanning speed repeating the above three
stages.
(a) input sampling stage in input sampling stage with scanning mode in turn, PLC
read into all input states and data, and will they deposited in the I/O image area within
the relevant units. Input sampling ended, turn to the user program execution and
output refresh stage. In these two stages, even if the input status and data changes,
I/O image area of state and the relevant unit data also won't change. Therefore, if the
input is the pulse signal, the pulse signal widths must be bigger than a scan cycle, can
ensure that in any case, this input all can be read.
(2) the user program execution stage
In the user program performance stage, PLC always press down the order of
sequence scanning the user program (ladder diagram). In a scanning each a ladder
diagram, and always first scan ladder-diagram left by all the contacts constitute
control circuits, and press first left, after the first under the order of the control by
contacts constitute the lines logic operations, and then based on the arithmetic logic
result, refresh this logic coil in system RAM storage area in corresponding a state; Or
refresh the output coil in the I/O image area in corresponding position state; Or to
determine whether to enforce the ladder-diagram prescribed by the special function
instructions.
Namely, the user program execution process, only input points in the I/O image
zone state and data will not change, and other output points and soft equipment in the
I/O image area or system RAM storage area of state and data is likely to change, and
row at top of the ladder diagram, its program to implement results of row who will the
next with these coils or data ladder diagram matters; Instead, row below the ladder
diagram, the logic of the coil set state or data only to the next in line to scan cycle it
plays a role in the program.
In the process of program execution if used immediately I/O instructions can be
direct access I/O points. Namely, use I/O instructions of words, input process image
registers value is not update, program directly from the I/O modules, output value will
be immediately image registers with renewals this input some difference immediately.
(3) output refresh stage
When scanning the user program ended, PLC came into output refresh stage.
During this period, the CPU according to the I/O image area of state and the
corresponding data refresh all the output latch circuit, then after output circuit driver
corresponding peripherals. At this moment, is the real output of PLC.
Three, PLC internal operation mode
Although the use of ladder diagram of PLC program is usually used to many
relays, timer and counter, but such names on internal not entity with PLC, but these
hardware in the memory and program program mode, and doing logic control editing
by output elements are connected by external mechanical devices do entity control.
So can greatly decrease the controller required hardware space. In fact PLC
executive ladder diagram program mode of operation is will ladder diagram works by
first code scanning mode read in the execution of the CPU control operation. In whole
the scanning process includes three steps, "input state examination", "the program
execution", "the output state update" that is as follows:
Step one "input states check" : PLC first check the input devices connected to
each point switch or sensor state (1 or 0 (on or off), and its status in the memory of the
corresponding position write Xn. Step 2 "code-execution" : will ladder diagram
programs perform take into the CPU, if the program execution in operation need input
contact state, direct from the memory inquires CPU removed. The operation result is
output coil deposit in corresponding position, memory does not react to the output
transient Yn. Step 3 "output status update" : will the output state step 2 update to the
PLC output department contact, and back to step 1. Of the three steps called PLC,
and completed scanning cycle the time needed for the reaction time, called PLC PLC
input signal if less than this time reaction time, are misreading of possibility. After the
program execution with the next time before the program execution, output and input
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