Friday, 2 January 2015

Response Time (PLC)

The total response time of the PLC is a fact we have to consider when shopping for a PLC. Just like our brains, the PLC takes a certain amount of time to react to changes. In many applications speed is not a concern, in others though...

If you take a moment to look away from this text you might see a picture on the wall. Your eyes actually see the picture before your brain says "Oh, there's a picture on the wall". In this example your eyes can be considered the sensor. The eyes are connected to the input circuit of your brain. The input circuit of your brain takes a certain amount of time to realize that your eyes saw something. (If you have been drinking alcohol this input response time would be longer!) Eventually your brain realizes that the eyes have seen something and it processes the data. It then sends an output signal to your mouth. Your mouth receives this data and begins to respond to it. Eventually your mouth utters the words "Gee, that's a really ugly picture!".

Notice in this example we had to respond to 3 things:

INPUT- It took a certain amount of time for the brain to notice the input signal from the eyes.

EXECUTION- It took a certain amount of time to process the information received from the eyes. Consider the program to be: If the eyes see an ugly picture then output appropriate words to the mouth.

OUTPUT- The mouth receives a signal from the brain and eventually spits (no pun intended) out the words "Gee, that's a really ugly picture!"

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