Note 1 – The CTU instruction uses a counter which is specified internally to the PLC.
Note: The underflow status signifies that the counter has reached the logical limit of -32768 and had to wrap back to the value of 32767.
UN – Boolean value which is set to HIGH when the counter is underflown.
Note2: To avoid overloading the counter, make sure to program proper measures into your software.
Note: The overflow status signifies that the counter has reached the logical limit of 32767 and had to wrap back to the value of -32768.
OV – Boolean value which is set to HIGH when the counter is overflown. DN – Boolean value which is set to HIGH when the timer is finished counting. CD – Boolean value which is set to HIGH when the counter is energized to count down. CU – Boolean value which is set to HIGH when the counter is energized to count up. ACC – Integer specifying the current time value of the timer. PRE – Integer specifying up to which value the timer will count.
Counter – The high-level instruction specification of all the inner structures.
The CTU leverages a specific data structure, called the Counter, present in most PLC systems. This will need to be implemented and tied into a button which is activated at the end of a shift for example. Note that the counter which keeps track of the number of batches produced does not have a reset. The process will repeat again for each batch. DN bit will also trigger the RES instruction which will set the “Accum” of C5:0 Counter back to 0. This instruction will keep track of the batches finalized in the process. DN bit will set an internal bit which will energize another CTU instruction. The process will continue until the counter has reached the value of 16.Īt 16, the counter will set the C5:0.DN bit because “Accum” = “Preset”. This value will continue to increment every single time a new product goes by. As soon as the switch detects the product, it energizes the CTU and increments the “Accum” value. This switch detects a certain product when it comes by on a conveyor belt. The CTU instruction is tied to the XIC which is energized by a proximity switch.
The B3:0/14 bit is also used to RES (Reset) the C5:0 Counter.
This Counter counts how many batches have been completed.
The B3:0/14 bit is used to energize C5:1.
The C5:0.DN bit is used to set an internal bit B3:0/14.
When “Accum” of C5:0 Counter is equal to 16, the C5:0.DN bit is HIGH.
The counter will continue to increment until “Accum” = 16.
When the bit B3:0/16 goes LOW, followed by HIGH, the CTU instruction is energized and the counter increments again.
When the bit B3:0/13 goes HIGH, the CTU instruction is energized and the counter increments the “Preset” value.
The number 16 represents the number of products in a certain batch.
The Counter C5:0 has a “Preset” of 16.
A CTU instruction is tied to Counter C5:0.
A “Product PROC Sensor ON” is indicated by an internal bit B3:0/13.
A Micrologix 1100 Allen Bradley PLC is used to control a process.
Here’s a real-world scenario of a CTU instruction: The CTU instruction must be paired with a way to reset the counter through a RES Instruction. It’s a widely used instruction which is extremely versatile and easy to work with. This critical element of ladder logic programming allows a programmer to keep track of how many products have passed a certain sensor, how many revolutions have been made by a certain motor, how many times a certain alarm was set and so on. Unline the Timer Instruction, the CTU will not keep incrementing until the rung is set to LOW and comes back to being HIGH. The CTU instruction will increment the “Accum” value each time the logic which leads into it is set to TRUE. Ī message coming directly from the Voice of the Dolomites: an invitation to love them, because where there is love, there is also respect.The CTU, also known as the Count Up, instruction is used in pair with a Counter construct to count the number of LOW to HIGH transitions of the preceding logic. The 88 photographs celebrate the magnificence of these special encounters and stir emotions that strongly convey the values of respect for, and protection of, the natural environment as the personal "home" heritage of each one of us. The Voice of the Dolomites” is a photo book that conveys the amazing beauty of the Dolomites through the eye of a photographer listening to its precious messages.įive years and 300 days up there on the field listening to this voice, in any season and any weather condition.
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