An Instrument may be defined as a device or a system which is designed to maintain a functional relationship between prescribed properties of physical variables and must include ways and means of communication to a human observer.
Functional Elements of an Instrumentation System
Most of the measurement system contains following main functional elements as shown in figure
- Primary Sensing Element
- Variable Conversion Element
- Variable Manipulation Element
- Data Transmission Element
- Data Presentation Element
1. Primary Sensing Element
The Measurand is first detected by the primary sensing element. The primary sensing element transfers the measurand to variable conversion element for further processing. The output signal of a primary sensing element is a physical variable such as displacement or voltage.
2. Variable Conversion Element
The output signal of a primary sensing element may require being converted to more suitable variables while preserving its information content. This function is performed by variable conversion element and it may be considered as an intermediate transducer
3. Variable Manipulation Element
This element is an intermediate stage of a measuring system. It modifies the direct signal by amplification, filtering, etc; so that the desired output is produced the physical nature of the variable remains unchanged during this stage.
4. Data Transmission Element
When the functional elements of the measuring system are spatially separated then it becomes necessary to transmit signals from one element to another. This function is performed by data transmission element. It is an essential functional element where remote control operation is desired.
5. Data Presentation Element
Usually, information about the quantity being measured is to be communicated to a human observer for monitoring control and analysis purpose. This is, therefore, to be presented in form of the human sensory capability. This function is done by data presentation element.
Functions of Instruments and Measurement Systems
Instruments or measurement system are classified based upon the function they performed.
1. Indicating Function: Different kinds of methods for supplying information concerning the variable quantity under measurement.
2 Recording Function: Stores or write the value of a quantity under measurement.
3. Controlling Function: In this case, the information is used by the instrument or the system to control the original measured.