Electrical and Electronic Engineering Department
ELEG3243 Programmable Logic Controllers
PLC Laboratory 6
Timer and Counter
Name:
Due Date:
Submission Date:
Lecturer:
23 Oct 2015
Tan Teck Siang
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OBJECTIVES
1. To learn the basic of timer and counter.
2. To design simple timer and counter ladder diagram
EQUIPMENT AND SUPPLIES
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Mitsubishi FX1s-30MR PLC
PC
Toggle Switches
PC with Mitsubishi MELSEC Programmer
3HP Air Compressor
Pneumatic Cylinder with reed switches
Pneumatic valves
INTRODUCTION
Timer
Mitsubishi PLC’s offers several time base Timer as shown below:
Timers by default are non-retentive. That means that they do not hold their value if the input circuit opens.
Timers T0~T199 are 100 millisecond timers, T200~T245 are 10 millisecond timers, for this CPU. The K
value is a multiplier. K123 means 123 x 100 milliseconds = 12.3 seconds. After the timer reaches 123, the
T0 contact will close.
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Counter
Counter Presets
Presets are the number of times the rung driving the counter has to go through a FALSE to TRUE state
transition before turning on. 16 bit counters have a range of 1 to 32,767. Counter presets can be either a K
constant, or a variable, such as a data or file register. Having a D device as the preset allows an operator to
make changes to the counter preset from an HMI.
The accumulated value of the timer never goes above the preset value. Once the counter coil has turned on,
it will remain on until reset. Even the use of the Decrement instruction to reduce the count will not
deactivate the counter coil.
Counting direction
16 bit counters only count up.
Counter Reset
The accumulated value of a counter returns to 0 when the RST C# instruction is activated.
Counter Example:
Counter
X000
K3
|-------| |-------------------------- (C000) --------|
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When X000 is cycled ON and OFF, the counter C000 will be incremented by 1. C000 will be turned ON
when it counts to 3.
Part 1 Basic Timer Ladder Diagram
Program the PLC with the ladder diagram below and record down your observation.
X000 T000
|-------| |--------|/| ----------- (Y000) --------|
Y000
|-------| |----Y000
|-------| |---------------------- (T000 K100) --------|
Observation:
Part 2 Basic Counter ladder diagram
Program the PLC with the ladder diagram below and record down your observation.
X000
K3
|-------| |-------------------------- (C000) --------|
C000
|-------| |-------------------------- (Y000) --------|
X001
|-------| |-------------------- [RST C000] --------|
Observation:
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Part 2 Solving Problem Using Timer and Counter.
Program and verify using the PLC for the process as described below.
Operation:
(a) When the user presses the push button X0, the cylinder extends after waiting for 3 seconds.
(b) The cylinder extends stroke after the user press the push button X0 three times.
(c) When the user presses the push button X0, the cylinder extends after waiting for 5 seconds. If the user
pressed the push button X1 before 5 seconds timeout, the cylinder will cancel the extension stroke.
(d) If the user pressed X0 for the first time, the cylinder extends. If the user pressed X0 for the second time,
the cylinder will retracts.
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(e) Continue from the previous step (d). If the user pressed X0 for more than 5 times, the cylinder will delay
2 seconds before extension or retraction.
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