Introduction:

An instrument is a device in which we can determine the magnitude or value of the quantity to be measured under observation. The measuring quantity can be voltage, current, power and energy etc.

Electrical systems must be tested for proper operation when they are installed and also periodically for maintenance purposes. The use of electronic test equipment, instruments, and meters generally involves:

1. Troubleshooting electrical/electronic circuits and equipment.
   

2. Verifying proper operation of instruments and associated equipment.
   

Now a days, there are two types of instruments available

1. Analog instruments
   

2. Digital instruments
   
   

Analog Instruments:

In analog instruments measure of quantity has been taken as the position of moving pointer on a dial/scale. In these instruments possibilities of human error exists and its possible accuracy is approx. 0.25%.

If exact reading is required operator takes more time to guess the approximate tenths of small division.

An analog instrument is one in which the output or display is a continuous function of time and bears a constant relation to its input.

The analog instruments find extensive use in present-day applications although digital instruments are increasing in number and applications.

The areas of application which are common to both analog and digital instruments are fairly limited at present.

Hence, it can safely be predicted that the analog instruments will remain in extensive use for a number of years and are not likely to be completely replaced by digital instruments for certain applications.

Digital Instruments:

In digital instruments measure of quantity has been taken as a number. In these type of instruments human error doesn’t exist and its possible accuracy is 0.005%.

Its time to observed reading is very fast. These instruments are calibrated internally with the help of an internal standard stabilized source.

Due to several advantages of digital instruments such as high speed, errorless results, better resolution and greater accuracy over analog instruments, the popularity of digital instruments are increasing rapidly.

Quantization is the basis of working of a digital instrument. It is an act of transforming an analog signal into its digital form. Digital instruments are composed of logic circuits that carry out measurement of the quantities.

Basically there are three type of measuring instruments and they are:

1. Electrical measuring instrument
   
2. Mechanical measuring instrument
   
3. Electronic measuring instrument
   

Here we are interested in electrical measuring instrument.

Characteristics of instrument:

1. Accuracy: It is desirable quality in measurement. It is defined as the degree of the closeness with which instrument reading approaches the true value of the quantity being measured.
   

2. Sensitivity: It is also desirable quality in the measurement. It is defined as the ratio of the magnitude response of the output signal to the magnitude response of the input signal.
   

3. Reproducibility: It is again a desirable quality. It is defined as the degree of the closeness with which a given quantity may be repeatedly measured. High value of reproducibility means low value of drift.
   

List of electrical instruments:

1. Ammeter
   

2. Voltmeter
   

3. Wattmeter
   

4. Transformer
   

5. Electric motor