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 A Single Ended Signal Amplifier. 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.
A differential amplifier with a current input is shown in Figure 14.33 A Current Amplifier. Note that Rc converts a current to a voltage. The voltage is then amplified to a larger voltage.
The circuit in Figure 14.34 A Differential Input to Single Ended Output Amplifier 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.
The Wheatstone bridge can be used to convert a resistance to a voltage output, as shown in Figure 14.35 A Resistance to Voltage Amplifier. If the resistor values are all made the same (and close to the value of R3) then the equation can be simplified.