As referred in the previous post, a counter down timer (CTD) decreases the value of its content whenever the input changes its logic state. Its output true condition, is set by the user.
Typically, a single 7-segments display could display the number from 0 t 15 using a hexadecimal format. With this feature, we can use it to display a time in second up to 15 seconds.
In this example I create a 15 timer that turn on a lamp. Two input contacts use for starting and stopping the running timer. A 7-Segments display the remanding time in seconds. An output lamp L1 is turned on while the timer is still running.
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| A sample of this example ladder diagram |
Ladder diagram of this example list below.
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| Ladder diagram of this example |
There are two input negate type contact - Xreset and Xstart. When Xreset is true, the Rstart internal output coil is set. However, when the Xreset is true the Rstart and the reset count (C0) instruction is clear.
The internal output coil Rstart activates the rung number 0004. T0 has a delay of 500 mS creating a one second period of pulse that fed to the counter down timer (CTD). CTD output true whenever it's content is above 0 second.
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| Schematic diagram |
Click here to download the zip file of this ladder diagram example.
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