14.3 INPUT ISSUES

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Signals from transducers are typically too small to be read by a normal analog input card. Amplifiers are used to increase the magnitude of these signals. An example of a single ended signal amplifier is shown in Figure 14.32. The amplifier is in an inverting configuration, so the output will have an opposite sign from the input. Adjustments are provided for gain and offset adjustments.

Figure 14.32 A Single Ended Signal Amplifier

A differential amplifier with a current input is shown in Figure 14.33. Note that Rc converts a current to a voltage. The voltage is then amplified to a larger voltage.

Figure 14.33 A Current Amplifier

The circuit in Figure 14.34 will convert a differential (double ended) signal to a single ended signal. The two input op-amps are used as unity gain followers, to create a high input impedance. The following amplifier amplifies the voltage difference.

Figure 14.34 A Differential Input to Single Ended Output Amplifier

The Wheatstone bridge can be used to convert a resistance to a voltage output, as shown in Figure 14.35. If the resistor values are all made the same (and close to the value of R3) then the equation can be simplified.

Figure 14.35 A Resistance to Voltage Amplifier