Measurement Computing PC104-CTR10HD - Manual (Page 14)

5.0 ELECTRONICS AND INTERFACING
5.1 VOLTAGE DIVIDERS
If you wish to measure a signal which varies over a range greater than the input range
of a digital input, a voltage divider can drop the voltage of the input signal to the level
the digital input can measure.
A voltage divider takes advantage of Ohm's law, which states,
Voltage = Current * Resistance
and Kirkoff's voltage law which states,
The sum of the voltage drops around a circuit will be equal to the voltage
drop for the entire circuit.
Implied in the above is that any variation in the voltage drop for the circuit as a whole
will have a proportional variation in all the voltage drops in the circuit.
A voltage divider takes advantage of the fact that the voltage across one of the
resistors in a circuit is proportional to the voltage across the total resistance in the
circuit (Figure 4-1).
Figure 4-1. Voltage Divider
The object in using a voltage divider is to choose two resistors with the proper
proportions relative to the full scale of the digital input and the maximum signal
voltage.
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