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RLC-4 V1.79 Copyright © 1998 Link Communications Inc. 9/18/98
One more example will illustrate how to develop a conversion that is not listed in the chart. Let us
assume that we want to read the wind speed at our site and that we have an anemometer (wind
speed detector) that reads 10 volts at 100 MPH. Since the maximum voltage is between 5 and 25
volts, it will work nicely with the voltage divider in the circuit. We will assume that 0 volts are
produced when the wind is not blowing and that it increases linearly from there. That sets our zero
point to be zero. We must calculate our full scale reading as if it will occur at 25 volts, even though
the sensor will never put out that much voltage, because that is the 5 volt full scale reading at the
processor times the 5:1 voltage divider ratio. What we need to know is how fast the wind would
have to blow to give us a 25 volt signal. A simple ratio will give us the answer:
100 MPH = X MPH
10 volts 25 volts
Cross Multiplying: 100 * 25 = 10 * X, 2500 = 10 * X, X = 250 MPH
We now know that the low point is 0, the high point is 250, and that we need to use the voltage
divider.
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