Functional Elements of an Instrument

FUNCTIONAL ELEMENTS OF AN INSTRUMENT

Most of the measurement systems contain three main functional elements. They

(i) Primary sensing element

(ii) Variable conversion element 

(iii) Data presentation element.

● Primary sensing Element: which senses the quantity under measurement.

● Variable conversion Element: which modifies suitably the output of the primary sensing element.

● Variable Manipulation Element: The signal gets manipulated here preserving the original nature of it.

● Data Transmission Element: The transmission of data from one another is done by the data transmission element.

● Data presentation Element: The display or readout devices which display the required information about the measurement.

Primary sensing element

The quantity under measurement makes its first contact with primary sensing element of a measurement system here, the primary sensing element transducer. This transducer converts measured into an analogous electrical signal.

Variable conversion element

The output of the primary sensing element is the electrical signal. It may be a voltage a frequency or some other electrical parameter. But this output is not suitable for this system.

For the instrument to perform the desired function, it may be necessary to convert this output to some other suitable form while retaining the original signal. Consider an example, suppose output is an analog signal form and the next of system accepts input signal only in digital form. Therefore we have to use analog to digital converter in this system.

Variable manipulation element

The main function of variable manipulation element is to manipulation element is to manipulate the signal presented to it preserving the original nature of the signal. Here, manipulation means a change in numerical value of the signal.

Consider a small example, an electric amplifier circuit accepts a small voltage signal as input and produces an output signal which is also voltage but of greater amplifier. Thus voltage amplifier acts as a variable manipulation element.

Data presentation element

The information about the quantity under measurement has to be conveyed to the personal handling the instrument or system for control or analysis purposes. The information conveyed must be in the form of intelligible to the personnel. The above function is done by data presentation element.

The output or data of the system can be monitored by using visual display devices may be analog or digital device like ammeter, digital meter etc. In case the data to be record, we can use analog or digital recording equipment. In industries, for control and analysis purpose we can use computers.

The final stage in a measurement system is known as terminating stage. when a control device is used for the final measurement stage it is necessary to apply some feedback to the input signal to accomplish the control Objective.

The term signal conditioning includes many other functions in addition to variable conversion and variable manipulation. In fact the element that follows the primary sensing element in any instrument or instrumentation system should be called signal conditioning element.

When the element of an instrument is physically separated, it becomes necessary to transmit data from one to another. This element is called transmitting element. The signal conditioning and transmitting stage is generally known as intermediate stage.