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Version 1.73 Copyright © 1997 Link Communications Inc. 1/18/97
"Resolution" refers to how many digits after the decimal place you want to know about.
Temperature is usually read to the nearest degree, zero digits after the decimal. When reading a
battery or power supply's voltage, you probably want to hear more than "thirteen volts" or
"fourteen volts", something like "thirteen point six volts". To obtain this kind of reading, you
would specify one digit after the decimal point.
The "conversion ratio" specifies how the controller interprets the voltage it detects. It could
also be called the "scale" or "meter faceplate". If you are measuring wind speed, you may want
a reading that varies from zero to 100 MPH. If wind direction, zero to 360 degrees. If pH, zero
to 14. If temperature, way below zero to a hundred degrees or more. No matter what scale you
want the reading to use, the voltage going into the analog line must be between 0 volts and 5
volts. If you have a sensor to measure something in the physical world that can provide a
voltage that varies between 0 volts and 5 volts, you can set up the conversion ratio to handle it.
The point of this discussion is to make it clear that the controller does not care what the real-
world quantity is, it just needs a variable voltage and the proper conversion ratio, and it can
handle it. You tell the RLC-Club what the conversion ratio is by specifying two points:
The first is what real world quantity would cause the sensor to output 0 volts. In many
cases this is zero. For example, if you are using a small motor with a propeller to detect
wind speed and the wind is not blowing, you will get 0 volts. But what about
temperature? If our sensor outputs 0 volts for zero degrees, how would we get negative
temperature readings? The analog lines can only accept positive voltages. The answer
is that we use a temperature sensor that outputs about 2.5 volts at zero degrees, less than
that when below zero and more than that when above zero. So our first conversion point
for temperature says that it would have to be 460 degrees below zero to get 0 volts out
of the sensor.
The second point we set specifies what real world quantity would cause the sensor to
output 5 volts. If your wind speed detector outputs 5 volts when the wind is blowing
150 MPH, this point would be 150. For the temperature sensor we use (the LM335), it
would have to be 440 degrees out to get 5 volts out of the sensor.
"Calibration" refers to correcting for small errors in a reading. If your the controller tells you it
is 85 degrees when it is 88, you can calibrate it to correct for the small error. If it is way off,
you probably have the conversion set wrong.
You can also set "analog alarms". These will cause a macro to be executed whenever the value
read on one of the analog lines goes above or below a preset value. See Commands 104..107
for more information.
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