Sample and hold circuitry

Noncontinuous measurements, such as those produced by the sample-and-hold circuitry of a chromatograph, can introduce significant deadtime into a loop. Also, the nature of the periodic step change in value prevents the use of derivative action in the controller. 

A different approach is to use a sample-and-hold circuitry on the analog outputs, and then multiplex them into a single ADC. This significantly increases the ADC conversion rate needed, which requires a significantly higher bandwidth. Since noise is also based on the bandwidth, this also can significantly increase the noise in your system. 

Multifunction boards are commonly used to measure analog signals. It is done by the ADC, which converts the analog voltage level into a digital number that the computer can interpret. The analog multiplexer (MUX), the instrumentation amplifier, the sample-and-hold (S/H) circuitry, and the ADC comprise the analog input section of a multifunction board (see Fig. 18.26). 

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