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6.0 ANALOG ELECTRONICS
This short introduction to the analog electronics most often needed by data acquisition
board users describes the following:
Voltage dividers.
Differential vs. Single Ended Inputs.
Isolation vs. Common Mode Range
Low pass filters for analog and digital inputs.
A/D Resolution
Conversion to Engineering units.
4-20 mA inputs
Noise; sources and solutions.
Digital interfacing.
Each deals with the impact on measurements made with data acquisition boards. For
additional information on the subject of data converters and analog electronics, Radio
Shack has written an excellent Op Amp handbook and has an Op Amp experimenters
kit.
A more advanced treatment is in the Analog-Digital Conversion Handbook (32.95)
and the Transducer Interfacing Handbook ($14.50) published by Prentice-Hall.
6.1 VOLTAGE DIVIDERS
If you wish to measure a signal which varies over a range greater than the input range
of an analog or digital input, a voltage divider will drop the voltage of the input signal
to the safe level the analog or 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.
Thus, 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 (Figure 6-1).
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