Chapter 14 PLC Function
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C200 Series
14-10
or double word. Furthermore, the two equipments, timer and counter, in PLC not only have coil
but also value of counting time and times.
In conclusion, each internal storage unit occupies fixed storage unit. When using these
equipments, the corresponding content will be read by bit, byte or word.
Brief introduction to the internal devices of PLC:
Internal Device
Function
Input Relay
Input relay is the basic storage unit of internal memory that corresponds to
external input point (it is the terminal that used to connect to external input switch
and receive external input signal). Input signal from external will decide it to
display 0 or 1. You couldn’t change the state of input relay by program design or
forced ON/OFF via WPLSoft. The contacts (contact a, b) can be used unlimitedly.
If there is no input signal, the corresponding input relay could be empty and can’t
be used with other functions.
;
Equipment indication method: X0, X1…X7, X10, X11… The symbol of
equipment is X and numbering in octal.
Output Relay
Output relay is the basic storage unit of internal memory that corresponds to
external output point (it is used to connect to external load). It can be driven by
input relay contact, the contact of other internal equipment and itself contact. It
uses a normally open contact to connect to external load and other contacts can
be used unlimitedly as input contacts. It doesn’t have the corresponding output
relay, if need, it can be used as internal relay.
;
Equipment indication: Y0, Y1…Y7, Y10, Y11… The symbol of equipment is
Y and numbering in octal.
Internal Relay
The internal relay doesn’t connect directly to outside. It is an auxiliary relay in
PLC. Its function is the same as the auxiliary relay in electric control circuit. Each
auxiliary relay has the corresponding basic unit. It can be driven by the contact of
input relay, output relay or other internal equipment. Its contacts can be used
unlimitedly. Internal auxiliary relay can’t output directly, it should output with
output point.
;
Equipment indication: M0, M1…M799. The symbol of equipment is M and
numbering in decimal system.
Counter
Counter is used to count. It needs to set counter before using counter (i.e. the
pulse of counter). There are coil, contacts and storage unit of counter in counter.
When coil is from OFF to ON, that means input a pulse in counter and the counter
should add 1. There are 16-bit, 32-bit and high-speed counter for user to use.
;
Equipment indication: C0, C1… C79. The symbol of equipment is C and
numbering in decimal system.
Timer
Timer is used to control time. There are coil, contact and timer storage. When coil
is ON, its contact will act (contact a is close, contact b is open) when attaining
desired time. The time value of timer is set by settings and each timer has its
regular period. User sets the timer value and each timer has its timing period.
Once the coil is OFF, the contact won’t act (contact a is open and contact b is
close) and the timer will be set to zero.
;
Equipment indication: T0, T1…T159. The symbol of equipment is T and
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