PRIMARY SENSING ELEMENT :
Primary sensing element of an instrument is that which first receives energy from measured medium and produces an output depending on the value of the measured quantity.
VARIABLE CONVERSION ELEMENT
A Variable conversion element converts the output of the Primary sensing element into a more suitable form or condition useful to the function of the instrument. Every instrument need not require a variable conversion element, while some require several.
VARIABLE MANIPULATION ELEMENT
Variable manipulation element manipulates the signal represented by some physical variable, to perform intended task of an instrument. In the manipulation process, the physical nature of variable is preserved.
DATA TRANSMISSION ELEMENT
Data transmission transmits data from one element to another. It may be as simple as shaft and bearing assembly or as complicated as a telemetry system for transmitting signal from one place to another.
DATA PRESENTATION ELEMENT
Data presentation element performs the translation function, such as simple indication of pointer moving over a scale or the recording of a pen moving over a chart.