Measurement-computing CIO-DAS16/330 Manual de usuario descargar pdf (Pagina 25)

6 ANALOG ELECTRONICS

This short introduction to the analog electronics most often needed by data acquisition board users covers a few key

concepts. They are:

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.

Each deals with the impact on measurements made with data acquisition boards.

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 can drop the voltage

of the input signal to the level the analog or digital

input can measure (Figure 6-1).

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.

Figure 6-1. Voltage Divider

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.

The trick to using a voltage divider is to choose two resistors with the proper proportions relative to the full scale of the

analog or digital input and the maximum signal voltage.

The phenomena of dropping the voltage proportionally is often called attenuation.

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Measurement-computing CIO-DAS16/330 Manual de usuario Pagina 25