Structure of measurement systems   The measurement system consists of several elements or blocks. It is possible to identify four types of element, although in a given system one type of element may be missing or may occur more than once. The four types are shown in Figure and can be defined as follows. General structure of measurement system Sensing element This is in contact with the process and gives an output which depends in some way on the variable to be measured. Examples are: Thermocouple where millivolt e.m.f. depends on temperature Strain gauge where resistance depends on mechanical strain Orifice plate where pressure drop depends on flow rate. If there is more than one sensing element in a system, the element in contact with the process is termed the primary sensing element, the others secondary sensing elements. Signal conditioning element This takes the output of the sensing element and converts it into a form more suitable for further processing, usually a d.c. voltage,