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Function block (FB) is a function to make to the component, and to recycle the circuit pattern and the operation pattern used repeatedly in the sequence program. The circuit block was done pasting copy &, and the device number was transferred or a complete making to the Black Box was not able to be done, it became a program not understood easily, and it caused the strike mistake of the device number though the same thing had been achieved by the CALL instruction by using the pointer so far. |
Commentor / R.Takeuchi |
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Attractive FB (1) |
The advantage of FB is a point that it is possible to select it even in the ladder and the ST language, according to needs are able to do making of the program of complete a Black Box. FB is only mere "Box" with the input value and the output value, exists when seeing from the ladder circuit, and it is not necessary to see the content of the processing. For example, it is a mechanism that the engineering value returns as a result when FB of the scale conversion is made, and five (engineering minimum value of raw data, raw data maximum value, engineering maximum value, and minimum value and raw data) are passed as an input variable.
The arithmetic expression variable expression of actual scale conversion is as follows.
If this arithmetic expression is written with the ladder, it becomes the following. Here explain as an example of the case of the ladder though it is also possible to write in FB in the ST language.
When FB where the above mentioned logic is described is arranged in the main program, and the input variable is allocated, it becomes the following. In this example, value (D0) of 0-4000 taken returns from the analog to digital translation unit in actual engineering value (0-3000) and the result that converts the scale returns to D100. In the monitor value, if "1100" is input, it is understood that the engineering value of "825" returns.
In case there are a lot channels from the analog to digital conversion that converts the scale, it is easily to debug, display many FB made Black Boxes more completely than doing the ladder block, doing in copy & paste, and it is smart.
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Inside MELSEC
Advanced OPC