If understood as PLC ladder diagram circuit, judging from the perspective of the relationship between the input and output are both combinational and sequential circuits, if according to the input of the deterministic case, circuit and random circuits have two.
(1) combination circuit
Output only with the input of the current situation, regardless of the input history of ladder diagram, called combinational circuits. Its characteristics are:
1) no feedback or no latch (or set) and count commands.
2) output state only by the receiver combination is a direct reflection of the State, the result is unique.
3) circuit state transitions can achieve at a time, with no intermediate state transitions.
4) required input elements, but the circuit is simple and reliable.
(2) sequential circuits
Not only the output and input related to the current situation, but also the inputs relating to the history of ladder diagram, called a sequential circuit. The simple sequential circuits, that is, with blackouts since lock link road. Characteristics of sequential circuits are:
1) feedback: the output coil is not only affected by the input signal control, directly or indirectly under the control of their contacts, or count or latch (or reset) instructions that can remember that has the status of the input signal.
2) solution: the same input status, can have a variety of outputs. Difference is determined by the input history of distinction. Circuit history of available counters, latch (or set) recorded feedback through contact can also be used to do the record.
3) order: sequential circuits solutions and actual values are determined by their work order. And work order is a rhythm, a beat. So-called rhythm refers to the two time intervals. PLC, input only as an end, interaction between internal components, or (feedback), but does not have to relay circuit, as input. It is order execution control, relay circuit competition like that is not a problem, so don’t have to beat a very fine.
Beats divided output can also be used, that is, it is defined as the interval between the two output changes. Analysis of sequential circuits to a rhythm, a beat analysis, design of sequential circuits, also to consider a rhythm, a beat.
Sequential circuits as a result of memory, input components required less. This input signal occasion for some of the more difficult to use, is a great convenience. Sequential circuits is more complex than combinational circuits. Study on time series, always assume that:
① at the same time there is only one input.
Two time intervals sufficient to enable PLC all instruction is executed.
Most PLC ladder diagram for sequential circuits, and these two assumptions, it can always be met.
It should be noted that this sequential circuits are asynchronous sequential circuits, controlled tempo sync pulse signal conversion there is no uniform.
(3) identification circuit
If the control object work process or sequence is determined, and its corresponding control circuit for determining circuit. Most PLC ladder diagram for determining circuit.
Determine first had to figure out the process of determining the design of the circuit or sequence, then according to the order or in the process of advancing progressive design.
Determine the combinations of circuits, there is timing. However, the timing more, because is sure, timing its juice, the input signal can be reduced.
Locate the electric power available table reflected its work.
(4) random circuits
Not sure if the work process or order, or is not fixed, unchanging, and its corresponding control circuit for random circuits.
Random circuits can also be powered up the table, that is to make it all possible are listed (if you can see it very clearly, “symmetry“ also is not included). Random circuit design process is possible, analyze its work processes, and design, finally integrated together, that is for the design of circuits.
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