The Analog Revolution and Its On-Going Role in Modern Analytical Measurements

Abstract

The electronic revolution in analytical instrumentation began when we first exceeded the two-digit resolution of panel meters and chart recorders and then took the first steps into automated control. It started with the first uses of operational amplifiers (op amps) in the analog domain 20 years before the digital computer entered the analytical lab. Their application greatly increased both accuracy and precision in chemical measurement and they provided an elegant means for the electronic control of experimental quantities. Later, laboratory and personal computers provided an unlimited readout resolution and enabled programmable control of instrument parameters as well as storage and computation of acquired data. However, digital computers did not replace the op amp's critical role of converting the analog sensor's output to a robust and accurate voltage. Rather it added a new role: converting that voltage into a number. These analog operations are generally the limiting portions of our computerized instrumentation systems. Operational amplifier performance in gain, input current and resistance, offset voltage, and rise time have improved by a remarkable 3-4 orders of magnitude since their first implementations. Each 10-fold improvement has opened the doors for the development of new techniques in all areas of chemical analysis. Along with some interesting history, the multiple roles op amps play in modern instrumentation are described along with a number of examples of new areas of analysis that have been enabled by their improvements.

The Elements of Measurement

“…The null principle is also fundamental to all operational amplifier circuits . These automated null systems are now subsections (conversion devices) in most modern measurement systems .…”

“…The null principle is also fundamental to all operational amplifier circuits. 14 These automated null systems are now In a null measurement system, the quantity being measured is compared with the output of an adjustable generator of the same quantity. The output Q 1 of the comparator (too large or too small) is used to adjust the standard quantity generator to bring the difference to zero.…”