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Welcome to Part 5 of our Mitsubishi GX Works 2 tutorial.
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We are going to discuss about Timers.
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The Mitsubushi FX PLC timer operates by counting
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clock pulses in 1 millisecond, 10 milliseconds or 100 milliseconds resolution.
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The timer device identifier is 'T'.
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It is a bit device with 0 (off) or 1 (on) output
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and the device address format is Decimal.
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The addressing of Timer is not the same as the X and Y devices
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which are limited to 0 to 7 or octal numbering system.
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The timers can be addressed from 0 to 9 decimal numbers.
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For example T0, T10, T11, T19, T20 and so on.
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The type of timer that we can use depends on the PLC type.
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For example, the FX1S PLC has normal timers only.
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It doesn't have retentive timers.
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The number of 100 ms timer for FX1S is only 63.
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It starts from T0 to T62.
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It has only 1 timer for the 1 ms resolution and it is T63.
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For the FX1N PLC there are 200 numbers of 100 ms normal timer from T0 to T199
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and there 6 numbers 100 ms retentive timers from T250 to T255.
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Retentive timers retains its present value even if the plc is stopped or there is a power failure.
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Once the plc is run again or the power is back, and the driving contact is closed
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the retentive will continue its counting from where it left off.
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Therefore the type of timer depends on the PLC type.
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This is how a timer program for an FX PLC is written.
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A drive input contact is needed to activate the timer.
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The timer uses an output coil symbol
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Press function key F7 or click the Coil symbol from the tool bar.
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Then enter the timer number, space and the constant K followed by the preset value.
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This is how timer preset value is computed.
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For a 10 seconds preset value with a 100ms timer resolution,
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looking at the FX1N timer device table, for 100 ms resolution, the available timer is from T0 to T199.
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Preset value in milliseconds divided by timer resolution.
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Converting 10 seconds to milliseconds equals to 10,000 milliseconds
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then divide by 100 milliseconds equals to 100.
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Therefor a 10 seconds preset value is equivalent to 100 K constant.
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We will add a timer contact to activate an output coil.
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Compile the program then we will simulate.
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We will close this contact.
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We can see that the timer starts counting.
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If we switch off the input contact the counted value goes back to 0.
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That is because this timer is normal timer and not a retentive type.
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We switch on again the drive contact.
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When the preset value of 10 seconds is reached,the timer contact will close.
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To open the timer contact and reset the timer the drive contact must be opened.
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That is how a normal Mitsubishi FX PLC timer works.
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There is also a retentive timer.
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This different from normal timer has the ability to retain
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the currently reached present value even after the drive contact has been removed.
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These are the retentive timers and these are the addresses.
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For FX1N, from T250 to T255.
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For FX3S from T131 to T137 for 100ms resolution.
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For FX3G 1ms resolution, from T246 to T249,
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the same as for FX2N.
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So the retentive timer depends on the PLC type except for FX1S
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Let us make an example for retentive timer.
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For example we need a 15 seconds timer, the constant should be 150.
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If we open the drive contact the counted value is retained.
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It did not reset to 0.
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When we switch on again the drive input X1, the counting continues.
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When it reaches the preset constant value of 150
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its contact will close and the output coil will be activated.
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Even if the drive contact will be switched off
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The timer is not reset.
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For retentive timers a reset instruction is needed.
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We simulate again this retentive timer.
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Switch off the drive input. The counted value is retained.
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We need to close this contact to activate the Reset instruction.
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We can see that the retentive timer has been reset and its contact is also opened.
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That is all for now for the basics of Mitsubishi FX PLC timers.
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For the next tutorial we will be discussing how to implement an Off delay timer on FX PLC.
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FX PLCs don't have built in off delay timers
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so we will make a small program using an ordinary timer.
