Functional Elements of an Instrument

Unit - V

Chapter 5

MEASUREMENTS AND INSTRUMENTATION

Functional elements of an instrument, Standards and calibration, Operating Principle, types -Moving Coil and Moving Iron meters, Measurement of three phase power, Energy Meter, Instrument Transformers-CT and PT, DSO- Block diagram- Data acquisition.

FUNCTIONAL ELEMENTS OF AN INSTRUMENT

Primary sensing element senses the parameters from the measuring medium and given its output to the variable conversion element.

This sensing element consist of a sensor or a transducer. So this initial stage is called detector transducer stage.

Variable conversion element converts the sensors output into a form suitable for further operator or suitable for next stage. Eg: LVDT, potentiometer, Bourdon tube, all secondary transducers.

Variable manipulation element performs some manipulation operation on the previous stage output in order to make the signal suitable or to strengthen the signal for further stages. Eg: Linkage and gear, Amplifier

Variable conversion and variable manipulation element are combined called as data conditioning element.

Data transmission element transmits the data to the place where data is presented to the observer. Eg. capillary tube.

Finally data is stored in a memory device for future analysis. Or/ and data is presented to the observer with the help of data presentation element. Eg: Scale and pointer, digital display, chart recorder.

Example: Pressure Thermometer

Temperature is measured using pressure thermometer.

In this pressure thermometer. Thermometer bulb performs two operation it senses the temperature and it converts the sensed temperature value into pressure. So it forms primary sensing and variable conversion operation.

Data is transmitted through capillary tube. This instrument consist of another variable conversion element i.e Bourdon tube. Bourdon tube converts the liquid or gas pressure into motion. Free end of the Bourdon tube is moved according to the pressure this movement is not in a sufficient amount of strength to move a pointer.

Linkage and gear arrangement is used to get a sufficient strength this linkage and gear forms the variable manipulation element.

Scale and pointer forms the data presentation element. Pointer moves over the scale presents the data to the observer.

So each measuring instrument consist of these basic functional elements. Some having more than one variable conversion and some do not have data transmission element. The places of variable conversion element and data transmission element may differ for some instruments.