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Almost every PLC program includes a
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timer instruction. The Productivity mini
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PLC P1M-622 16 DR offers several timer
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We discussed the time coil TMC and
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flasher coil FLS in our last post as
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part of our discussion of contacts and
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In this session, we will review the
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instructions for the simple timer STMR
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and timer TMR in the Productivity Suite
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We will build on our start-stop motor
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circuit from earlier in this series and
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demonstrate practical timer examples
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that you can use in real programs.
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Detailed information contained in this
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video can be found at accautomation.ca.
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A link has been put in the description
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below. The website offers extensive
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links, references, and coding samples,
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making it a one-stop shop for all your
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Once again, that is accautomation.ca.
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Timing diagrams, Productivity timer.
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Timers are used in most PLC programs.
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Before writing a single rung of timer
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logic, it is important to understand the
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timing chart, also called a timing
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A timing chart is a visual
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representation of how inputs and outputs
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relate to each other over time.
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It shows you exactly when an output
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should turn on and off relative to its
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input, which determines which type of
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We have covered timing charts in detail
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in the following post, The Secret of
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Understanding the timing chart first
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will save you a great deal of
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troubleshooting time later.
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Always sketch your timing chart before
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Simple timer STMR, on-delay timer.
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The simple timer STMR is the most
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straightforward timer in the
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It is found in the timer counter
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category of the instructions list. The
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STMR has two operating modes, on-delay
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On-delay, the output turns on after the
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input has been on continuously for the
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If the input turns off before the timer
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expires, the current value resets to
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zero and the timer restarts when the
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input turns on again.
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Setting up the simple timer using the
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When you add an STMR to your ladder, you
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will be prompted to enter the addresses
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individually or use the structure
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Select new structure, give it a name.
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For this example, we will use simple
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timer one. Using the structure
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automatically creates the following
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Simple timer one preset, 32-bit integer,
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the time value the timer counts to.
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Simple timer one current, 32-bit
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The current accumulated time value.
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Simple timer one done, Boolean, turns on
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when current reaches preset.
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Under the tag definitions, set the
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preset value to memory retentive so it
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survives a power cycle and enter an
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initial value of 100.
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The STMR time base is 100 milliseconds,
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0.1 seconds per count, so 100 counts
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Practical example with the start-stop
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Now add the STMR instruction to a new
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rung below your start-stop motor circuit
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a switch input, as the rung condition.
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Add a rung below the STMR instruction.
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Place a NO contact using simple timer
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one done as the tag and wire it to an
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out coil on DO001.1.2,
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a second relay output, an indicator
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Note, before testing our circuit, call
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up the tag database. We can turn on the
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forcible bits for the inputs and
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This will allow us to test all of our
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inputs and outputs on the CPU unit.
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Highlight the two new rungs and right
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Select the monitor and data view. In the
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monitor and data view window, select
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create new tab. Select okay.
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We can now monitor our new rungs.
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When DI0.1.1.3 is turned on, the timer
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begins counting. After 10 seconds, the
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done bit energizes and DO0.1.1.2
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turns off before the 10 seconds expire,
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the current value resets to zero. The
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This is a classic on delay application
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used whenever you want to delayed start.
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A conveyor that begins moving 10 seconds
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after a start signal, a warning horn
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that sounds after a door has been open
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for a set time, or a motor that needs a
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warm-up delay before a downstream
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>> Simple timer STMR off-delay timer.
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The off-delay timer keeps the output on
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for the preset time after the input
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The output is on while the input is on
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and remains on for the preset duration
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after the input drops.
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Setting up the off-delay.
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Add a second STMR instruction, select
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new structure and name it simple timer
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This creates the same three tags.
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Simple timer two preset 32-bit integer.
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Simple timer two current 32-bit integer.
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Simple timer two done Boolean.
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Set the preset to memory retentive with
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an initial value of 1,000, 10.00
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In the STMR instruction block, change
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the timer mode from on-delay to
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How it works. When the rung input DI
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turns on, the simple timer two done
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output bit immediately turns on.
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turns off, the timer begins counting.
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After 10 seconds, the done bit turns
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off. The timer's current value resets
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and is ready for the next cycle.
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Practical example with the start-stop
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circuit. Imagine you want the motor or a
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fan to continue running for 10 seconds
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after the operator presses stop.
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A fan motor run-down delay is allowed to
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allow for cooling before fully stopping.
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Wire the motor's running status [music]
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as the run condition for the off-delay
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Drive a second coil from the done bit
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that keeps a downstream device
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When the motor stops, the downstream
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device stays on for [music] the
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10-second run-down period.
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Tip: The on delay and off delay modes of
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the STMR can each be demonstrated
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clearly on a timing chart. Draw the
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input line and the output line before
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writing your rungs. The relationship
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between them will tell you exactly which
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Timer TMR, up-down timer with reset.
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The timer TMR instruction provides more
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flexibility than the simple timer. It
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supports independent up and down count
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inputs, a separate reset input, a
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selectable time base, and four
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comparison output bits.
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This makes it ideal for applications
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where you need to track elapsed time in
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multiple directions or trigger outputs
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at specific time thresholds.
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Setting up the TMR using the structure.
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Add a TMR instruction from the timer
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counter category. Select use structure
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and name it timer one.
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Set the time base to seconds. This
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creates the following tags.
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Timer one preset, a 32-bit integer.
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The target value for comparison.
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Timer one [music] reset, 32-bit integer.
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The value the current value is set to
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when reset is triggered.
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Timer one current, 32-bit integer. The
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current accumulated time in the selected
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Timer one less, Boolean.
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On when current is less than preset.
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Timer one equal, Boolean. On when
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current equals preset.
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Timer one greater, Boolean.
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On when current is greater than preset.
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Set preset, reset, and current to memory
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retentive. Set the preset initial value
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Time up input. Wire DI0.1.1.5
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as the time up input. When DI0.1.1.5
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is on, the timer counts up at the time
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base rate, 1 second per count.
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The current value increases toward the
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Time down input. Wire DI0.1.1.6
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as the time down input.
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is on, the timer counts down at the time
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base rate. The current value decreases.
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Important. When both time up and time
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down inputs are on simultaneously, the
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timer does not count in either
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>> It holds its current value until one
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Reset input. Wire DI0.1.1.7
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as the reset input. When DI0.1.1.7
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is activated, the timer's current value
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is set to the reset value, in our case,
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This clears the accumulated time and
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returns the timer to its starting state.
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Using the comparison outputs,
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the three Boolean output bits, less,
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equal, and greater, give you three
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trigger points from a single timer.
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For example, use timer one less to keep
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a green indicator light on while the
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timer is still below the preset, process
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Use timer one equal to trigger a single
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scan event when the timer hits exactly
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Use timer one greater to energize an
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alarm output if the process has run past
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Practical example with the start-stop
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Add the TMR to your program with the
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motor output, DO 0.1 1.1, as the time up
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The timer will now track exactly how
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long the motor has been running.
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Wire timer one greater to an output coil
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an alarm light that turns on if the
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motor has been running for more than 20
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seconds without an operator reset.
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Wire DI 0 1.1.7, a reset push button, to
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clear the accumulated time when the
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operator acknowledges the alarm.
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This gives you a basic run time exceeded
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alarm, a practical pattern used in many
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real industrial applications.
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>> Retentive versus non-retentive timer
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One important decision when configuring
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any timer in the Productivity Suite is
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whether to make the preset and current
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values memory retentive.
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A retentive tag retains its value
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through a power cycle. The value is
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stored in battery-backed memory and
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restored on power up.
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A non-retentive tag resets to its
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initial value on every power cycle.
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For the preset, retentive is almost
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always the right choice.
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You don't want your 10-second delay to
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become 0 seconds after a power
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For the current value, retentive is
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useful when you need to track
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accumulated time across power cycles.
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For example, a maintenance interval
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timer that should not reset just because
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the panel lost power briefly.
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Non-retentive is appropriate when the
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timer should always start fresh on power
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up, for example, during a startup delay.
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has on-board battery-backed memory to
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support retentive tags. This is covered
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in detail in the user manual, chapter 1,
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Here is a summary chart on choosing the
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The FLS flasher coil and TMC timed coil
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were covered in the contact and coil
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The STMR and TMR are the dedicated timer
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instructions for more precise time-based
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Next time, we will look at counter
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instructions in the Productivity mini
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Many PLC manufacturers offer a range of
15:13
hardware and software. All programmable
15:15
logic controllers share similar basic
15:18
Once you are familiar with the basics of
15:20
the PLC, you will learn the specifics of
15:22
the controller you will be programming.
15:24
This is the easiest way to learn about
15:26
PLC programming. Click here to see how I
15:28
would approach learning about basic
15:31
Click here to see how you can program
15:33
for free with the ACC PLC simulator with
15:35
3D scenes you can program.
