It is generally believed the number of input points is according to the input signal.
But in practice, through the following measures to save PLC input points, the purpose of the following to introduce FX1N series PLC.
method one: grouping input as shown in the figure below, the system has a 'manual' and 'automatic' two kind of way to work.
Use X000 used to identify the 'automatic' or 'manual' operation signal, 'manual' when the input signal is SB0 ~ SB3, 'automatic' when the input signal is S0 ~ S3, according to normal design train of thought, if you need to X000 ~ X007 a total of eight input point, if the way of design, referring to the following figure simply X001 ~ X004 a total of four input point.
the diode is used to cut the parasitic circuit diagram.
If no diode in the figure, the system is in automatic state, SB0, SB1, S0 closed S1 disconnect, when the current flow from COM terminal, SB0, SB1, S0 parasitic loop into the X000 terminal, input a X002 wrongly ON becomes.
After the switch series diode, cut off the parasitic loop, avoid the mistakes.
But using this method should consider the input signal strength.
method 2: matrix input as shown in the figure below, 4 * 4 matrix input circuit, which USES PLC
four input point (
And four dots (
Y000 ~ Y003)
To realize the function of the 16 input point, especially suitable for PLC output point not enough input point.
When Y000 conductivity, X000 ~ X003 from Q1 to Q4 is acceptable for the input signal;
When Y001 conductivity, X000 ~ Q5 is acceptable for the X003 ~ Q8 from input signal;
When Y002 conductivity, X000 ~ X003 Q9 ~ Q12 is acceptable for the delivery of the input signal;
When Y003 conductivity, X000 ~ X003 Q13 ~ Q16 is acceptable for the delivery of the input signal.
Will Y000 normally open point and X000 ~ X003 series as the input signal Q1 ~ Q4;
Y1 normally open point and X000 ~ X003 series as the input signal Q5 ~ Q8.
Will Y002 normally open point and X000 ~ X003 series as the input signal Q9 ~ Q12;
Will Y003 normally open point and X000 ~ X003 series as the input signal Q13 ~ Q16.
should be paid attention to when using: in addition to the wiring according to above, also must have the corresponding software
to cooperate, in order to realize Y000 ~ Y003 conduction in turn;
Even at the same time to ensure that the input signal should be greater than the width of Y000 ~ Y003 conduction in turn over time, otherwise may lose the input signal.
The shortcoming of this method is to make the input signal is reduced to a third of the original sampling frequency, and the output point Y000 ~ Y003 cannot be used again.
3: method combined input for input signal is not connected at the same time, can adopt the way of combination coding input.
As shown in the figure below, the three input signal SB0 ~ SB2 only occupies two input point, M0 and M2 respectively SB0 ~ SB2.
method 4: input point more functional in the traditional relay control system, a command (
Button, switch, etc. )
Makes a feature of the signal.
In PLC controller
control system, an input device under different conditions can produce different signals, such as a button can be used to produce both start signal, and can be used to generate the stop signal.
As shown in the figure below, use only one button to control through X000 Y000 'tong' and 'off'.
The first time through X000 Y000 'tong', through to X000 again Y000 'break', this method is called the 'non-locking a key start-stop button'.
method 5: input contact merge incorporating some features the same switch input device and input,
Normally closed contact series input, normally open contact parallel input)
Some protection circuit and alarm circuit is often adopted.
if some external input signal is always in a 'or' combination of overall form appeared in the ladder diagram, they can be some corresponding contact after external series-parallel programmable controller input programmable controller as a whole, only an input point of programmable controller.
such as more than one load can be in place to start and stop, multiple start signal can be connected in parallel, series will stop multiple signal, respectively for programmable controller of two input point, as shown in the figure below.
With each start and stop signals compared to occupy an input point method, not only save the input point, also simplifies the ladder diagram circuit.
method 6: some PLC input signal does not enter the some of system signal features simple, narrow, the manual button in the diagram below, overload protection of thermal relay contacts, etc. , sometimes it is not necessary as input of PLC, PLC to design them in the peripheral hardware circuits can also meet the control requirements.
If the external hardware circuit is too complex, should consider will still be the signal into the programmable controller.
method seven: use the RUN mostly PLC have RUN mouth mouth, and only the mouth connected (
RUN to COM with wires between sub)
can RUN, so that put some input signal in the RUN.
When making the design of elevator control system, once the elevator traction motor overload protection of thermal relay normally closed contact, security window switch is normally open contacts, safety clamp switch normally open contacts, upper and lower limit switch normally closed contact of series to RUN the mouth to the connection between COM.
when a traction motor overload safety gear, security window is opened, the movements and header and the failure condition such as sink, RUN the mouth is cut off, PLC stops running, both to ensure the safety of the elevator and passengers, can supervise the maintenance personnel for repair.
Do have the following two advantages, one is the traction motor overload, security window is opened and the fault signal is sent to PLC controller, also do not take up the input port of PLC;
The second is not achieved by software protection, can simplify the control program.
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