• The instruments of measurement are considered as systems of interconnected components organized to perform a specified function for the purpose of analysis and synthesis. The performance of measurement system can be described in terms of static and dynamic characteristic. It is desirable to describe the operation of a measuring instrument or a system in a generalized manner without restoring the details of the physical aspects of a measurement system. The whole operation is described in terms of functions elements. Each functional element is made up of a distinct component or groups of components which perform the required & definite steps in the measurement.

The functional elements:

Primary Sensing Element: The quantity under measurement makes its first contact with the primary sensing element of a measurement system. The physical quantity to be measured, in the first place is sensed & detected by an element which gives the output in a different analogous form. This output is then converted into an electrical signal by a transducer.

Variable Conversion Element: The output of the primary sensing element may be electrical signal of any form, as voltage, frequency or some other electrical parameter which is not always suited as output to all the system. Therefore, to perform the desired function it is necessary to convert this output signal to some other suitable form, preserving the information content of the original signal.

Variable Manipulation Element: The function of this element is to manipulate the signal presented to it preserving the original nature of the signal. Manipulation here means only a change in numerical value of the signal.

Data Transmission Element: An element that transmits the signal from one location to another without changing its information content is data transmission element. Data may be transmitted over long distances.

Data Presentation Element: The information about the quantity under measurement has to be conveyed to the personnel handling the instrument or the system for monitoring, control or analysis purposes. The information conveyed must be in a form intelligible to the personnel or to the intelligent instrumentation system. This function is done by data presentation element.

Example: Rudimentary Pressure Gauge

The primary sensing element is the piston, which also serves the function of variable conversion since it converts the fluid pressure (Force per unit area) to a resultant force on the piston face. Force transmitted by the piston rod to the spring, which converts force to a proportional displacement. The displacement of the piston rod is magnified (manipulated) by the linkage to give a larger pointer displacement. The pointer & scale indicate the pressure thus serving as data presentation elements.