eBook: Automating Manufacturing Systems; with PLCs



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 358. 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 358 A Single Ended Signal Amplifier

A differential amplifier with a current input is shown in Figure 359. Note that Rc converts a current to a voltage. The voltage is then amplified to a larger voltage.

Figure 359 A Current Amplifier

The circuit in Figure 360 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 360 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 361. If the resistor values are all made the same (and close to the value of R3) then the equation can be simplified.

Figure 361 A Resistance to Voltage Amplifier

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