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Welcome to Part 4 of our Mitsubishi GX Works 2 tutorial.
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Our topic is about the Set and Reset Instruction of Mitsubishi FX PLC.
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If you are familiar of latching circuit
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that is most used in relay logic direct on line motor starter
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this is almost the same function as the Set and Reset instruction of the PLC.
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Let us see the operation of an ordinary latching circuit.
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This is the stop button
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and this is the start button.
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If we activate the start button
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The output coil will be latched.
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Even if the start button is released the output is latched through this contact.
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If we press the stop button the latch will be released.
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The coil will then be deactivated.
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For the Set and Reset instruction
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This will be the start pushbutton and this will be the stop pushbutton
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and this is the output coil.
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If we activate this contact
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the output coil will be set.
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Even if the input contact is opened the output coil will remain On.
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In order to turn off the output coil
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the Reset instruction must be activated.
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That is the basics for Set and Reset instruction.
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Set and Reset instructions are not limited to latching applications.
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Reset is also used in PLC counter applications.
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For example in counters, if the Set value has been reached
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Reset should be used in order to return back to 0 count.
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We will see how it works.
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Even if the Preset value has not been reached,if the counter is reset
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the current count value will reset to 0.
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We will try to count up to the set value
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The counter coil is activated and its contact is closed
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The output coil is also activated.
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In order to open the this contact the counter must be reset.
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This input contact must be activated to reset the counter.
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For timer application, reset is used for retentive type timers.
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These are the timers that in the event the PLC is stopped
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or there is a power failure the running count value during the time the PLC stopped is retained.
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For example when we activate this X4 input contact
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the timer will start counting.
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Suppose this contact will open, the current count is retained.
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It has the capability to pause the counting or timing process.
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In order to continue the timing this input contact must be closed.
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Once the set value is reached the timer contact will close.
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The timer contact closed ang the output coil is energized.
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Even if this input contact is opened the timer will not reset.
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In order to reset the timer to 0, and to open the timer contact
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the timer has to be reset.
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That is how to use the Reset instruction for Retentive Timer.
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The timer can also be reset while in the middle of timing process.
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For data registers or other word devices its value can be reset.
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For example we have accummulated value in the data register,
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supposing there is a sensor in the input that counts finished products
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the accummulated number can be reset.
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We will see how it works.
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Every time the input goes high,
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the data register value is incremented due to the Increment Instruction.
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In order to reset the data register value to 0,
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we will provide a Reset Instruction to the data register.
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There is also a Zone Reset Instruction.
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This is used to reset in one time a range of bit devices, counters, timers or data registers.
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Example this range of auxiliary relays are set,
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we ran reset all of it in one time.
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For example from M10 to M12 can be reset in one time.
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The instruction is Zone Reset,
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This is the first destination device
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and this is the second destination device.
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The second destination device must be higher
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compared to the first destination device.
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The specified device range cannot contain mixed device types.
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For example a counter here and the other is a timer is not allowed.
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Devices must be of the same type.
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For example we set M10 to M13
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then we will reset in one time M10 to M12.
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The three auxiliary devices has been reset.
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M13 was not included because
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only the devices within the range is covered by the zone reset instruction.
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So we have to reset M13 individually.
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That is all for the basic tutorial on how to use the Set and Reset instruction.
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We will discuss the Timers on the next video tutorial.
