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ACC – Integer specifying the current time value of the timer. PRE – Integer specifying up to which value the timer will count. Timer – The high-level instruction specification of all the inner structures.The TON leverages a specific data structure, called the Timer, present in most PLC systems. In other words, when the “Accum” is equal to the “Preset”.

DN bit is set to HIGH once the timer reaches the final value. TT bit is set to HIGH while the timer is counting the “Accum” is less than “Preset”. EN bit will be set to HIGH if the timer is energized by the input instructions leading to it. The timer will set different auxiliary bits during operation. In other words, the timer will count to 2000 seconds. This translates to a 2000 x 1.0 multiplier for our time. It’s important to note that the “Time Base” of our timer is set to 1. In the example above, this value is set to 2000. The timer will begin counting at from 0 until it reaches the value specified by the “Preset” integer. The TON instruction will begin counting as soon as the B3:0/4 XIC is energized.

IF the B3:0/4 bit is set to LOW while the timer is counting, the Accum is set back to 0.

As the timer is initialized by the B3:0/4 XIC, it starts to count.

The “Accum” of T4:0 is set to 0 which translates to the timer starting to count from 0.

The “Preset” of T4:0 is set to 2000 which translates to the timer counting up to 2000 seconds.

The Time Base of T4:0 is set to 1.0 which translates to the timer counting in seconds.

The TON instruction specifies a Timer in the PLC: T4:0.

The bit above is tied to an XIC instruction which enables the TON instruction.

A “Tank Cooling Sequence” is initiated by an internal bit B3:0/4.

A Micrologix 1100 Allen Bradley PLC is used to control a process.

Here’s a real-world scenario of a TON instruction: Example: Once the motor is started, wait 5 second start the next step. If such an input is missing, it's possible to issue a timer delay that would assume that the motor is running after a certain time. In other words, once an output is set to start a motor, the user may receive feedback that confirms that the motor is running at speed. If there's a way to get the status of these elements, it's possible to avoid using timers.

As a process is initiated via a "start" push button, each element is started based on a sequence.

An example of a required timer would be during a startup sequence. A timer is needed in many PLC applications and is used to delay a certain condition. Depending on the application, you may not need to use all of them.Īn Allen Bradley timer instruction is common to be seen in RSLogix 5, 500, 5000 as well as Studio 5000. The TON instruction is a composite instruction which means that it will contain a timer, integers as well as booleans. Furthermore, experienced developers can leverage the instruction to know when a certain process is being executed. Once this value is reached, the program will set specific internal bits notifying the programmer as well as other instructions within the PLC that the timer has finished counting. The conditions preceding the TON instruction will allow the timer to start counting up to a specified value.

The TON, also known as Timer ON, an instruction is used to keep track of time of occurrence of certain events.