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RLC-4 V1.79 Copyright © 1998 Link Communications Inc. 9/18/98
Custom Analog Conversion Ratios:
If the conversions provided in the chart are what you need, don't bother reading this section. It
describes how to come up with your own conversions.
The conversion is simply a linear ratio. You provide a reading that corresponds with 0 volts at the
processor and another number that corresponds with 5 volts at the processor, and the controller just
does a linear interpolation.
First we will describe some of the conversions in the table, then illustrate how to come up with your
own:
0 to 5 volt, 1 volt resolution, no voltage dividers:
This is about as straightforward as it can get. When it reads 0, it converts it to zero. When
the processor reads 5 volts, it converts it to 5 volts.
0 to 5 volt, 1/10 volt resolution, no voltage dividers:
When it reads 0, it converts it to zero. To get 1/10 volt resolution, we need to use one digit
after the decimal point. Because of this we have to assume one decimal point when we enter the
conversion points. When the processor reads 5 volts, we need to convert to 50, which with one
assumed decimal place, is 5.0 volts.
0 to 5 volt, 1/100 volt resolution, no voltage dividers:
When it reads 0, it converts it to zero. To get 1/100 volt resolution, we need to use two
digits after the decimal point. When the processor reads 5 volts, we tell it to convert it to 500,
which with one assumed decimal place, is 5.00 volts.
Temperature in Celsius, 1 degree resolution, no voltage dividers:
The key to figuring this one out is knowing how the LM335 temperature sensor works. It
provides an output voltage of 10mV per degree kelvin. It should therefore output zero volts at
zero degrees kelvin. Zero degrees kelvin is minus 273 degrees celsius, so that is our first
conversion point, -273. The 5 volt conversion point would be reached at 5V/10mV per degree =
500 degrees kelvin, or 227 degrees celsius (above zero). This is our other conversion point.
Temperature in Fahrenheit, 1 degree resolution, no voltage dividers:
This conversion is very similar to the one for celsius temperature. 0 degrees kelvin is -460
degrees fahrenheit. 500 degrees kelvin is 440 degrees fahrenheit.
0 to 25 volt, 1 volt resolution, with the voltage divider:
The difference between this and the 5 volt conversion is the voltage divider. The divider
cuts the received voltage to 1/5 before passing it on to the processor. In other words, the zero
point does not change, but the full-scale reading is now 25 rather than 5 volts. Since we want it to
read 25 volts when we give it 25 volts, the zero point is 0 and the full scale point is 25. Seems too
easy, doesn't it?
The other resolutions of the 0 to 25 volt conversions are left to a comparison with the 5 volt
conversions.
Содержание RLC-4
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