Page 313 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

There are two types of timer:-
PLC on delay timer : The timer will be ON state when it receives a start input signal and the signal state of output
changes to 0 from 1 , when preset timing is reached. The signal state of the output changes from 0 to 1 when
preset time has been reached with reference to change of RLO(Result of logic operation) from 0 to 1(ON) at the
start input .Functional diagram Is shown in Figure 1.6

PLC off delay timer : The timer will be ON state when it receives a start input signal and The signal state of out-
put changes to 1 from 0 , when preset timing is reached. The signal state of theoutput changes from 1 to 0 when
preset time has been reached with reference to change of RLO from 1 to 0(OFF) at the start input. Functional
diagram is shown in Figure 1.7.

PLC counters
Counters are used to detect pieces numbers and events. Controllers frequently need to operate with counters in
practice. For example: a counter in circuit is required if exactly 20 identical components are to be conveyed to a
conveyor belt via a sorting device. There are two basic counter types a) Count Up b) Count down When the input
to 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 bit will be set. A count down counter will decrease the
accumulator value until the preset value is reached. Symbols are shown in Figure 1.8

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CITS : E & H - Electronics Mechanic - Lesson 180 - 187