Abstract
A fundamental structure for the measurement process is developed. Measurement is defined as the determination of the number of units of a particular quantity or property presented by the measured object or sample. Measurement is distinguished from qualitative observation and data interpretation. The limited sources of measurement numbers (scalar, digital, and counting readouts) reveal that all measurements except manual counting require a measurement device. Measurement systems consist of devices which convert one form of data encoding to another. They begin with the sensor and proceed through intermediate conversion devices until the readout device produces numbers. There are three classes of conversion devices: input (sensor), intermediate, and readout. The characteristics of the conversion devices in a system determine the overall system characteristics. Counting measurements have several unique characteristics. In automated counting, conversion devices are used in event detection, discrimination, and boundary setting. Variance in counting arises from event detection, boundary setting, and random event occurrence. Entire measurement systems or conversion device subsystems may operate by null comparison. Conversion devices in null comparison systems have a different arrangement. The time relationship of multiple or successive measurements affects the information content of data sets. Time-correlation of acquired data is critical in all stimulus-response measurement systems such as chromatography and time-of-flight mass spectrometry and in many subsystems such as lock-in amplifiers and box-car integrators.