Classification of Types of Measuring Instruments

The electrical and electronic measuring instruments can be broadly classified into following two types.

• Absolute instruments and
• Secondary instruments

Absolute Instruments

These are the instruments which give the value

Ammeter

Ammeter is an instrument that measures the flow of electrical current in amperes.

Symbol of Ammeter

The given below figure shows the symbol used to indicate an Ammeter.

Ammeter symbol

An Ammeter is always connected in series to the element through which the flow of current should be measured as shown in the below figure. It is because the current is common in a series circuit. An Ammeter should have very low impedance else if the ammeter has high impedance it will reduce the current in the circuit in which it connected. An ammeter should never be connected in parallel. As it has very low impedance, if it is connected in parallel it will allow high current and result in short circuit. Hence it must be always avoided.

Circuit for connecting an ammeter

Sensitivity of a Measuring Instrument

Sensitivity

Sensitivity is defined by the change in the output or response of the instrument for a unit change of input or measured variable

Resolution

Resolution is the smallest change in a measured variable which can be measured from the instrument.

Voltmeter

Voltmeter is an instrument to measure the voltage or potential difference. 

Symbol of Voltmeter

The given below figure shows the symbol used to indicate a voltmeter.

Voltmeter Symbol

A Voltmeter is always connected in

Accuracy

In measurements accuracy is defined as the closeness with which the measured value obtained by a measuring instrument is nearer to the true value of the measuring quantity.

Precision

Precision is a measure of reproducibility of measurements. Most repeated value or most reproduced value is called as precise value.

Precision never confirms accuracy.

If the measuring