Introduction:

An instrument is a device used to measure the magnitude or value of the specific quantity under observation. The quantities measured can include voltage, current, power, energy etc.

Electrical systems must be tested both during installation and periodically for maintenance to ensure proper operation. This testing often involves the use of electronic test equipment,instruments, and meters for purposes such as:

1. Troubleshooting electrical or electronic circuits and equipment.
   

2. Verifying the correct operation of instruments and related systems.
   

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:

Digital instruments display measurements as numerical values.These instruments eliminate human error and typically offer much higher accuracy,often around 0.005%.

Digital instruments provide readings almost instantaneously and are internally calibrated using a stabilized reference source.

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

The core principle of digital instruments is quantization, which converts analog signals into digital form.These instruments rely on logic circuits to perform their measurements.

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 Instruments:

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: Sensitivity is the ratio of the output signal change to the input signal change. Higher sensitivity means the instrument can detect smaller variations in the measured quantity.
   

Sensitivity depends on the units of both the input and output signals.For example, a voltmeter might have a sensitivity of millivolts per division.

3. Reproducibility: Reproducibility refers to the consistency of an instrument's readings when measuring the same quantity under the same conditions multiple times.
   

High reproducibility indicates good long-term stability, measuring the instrument's performance does not degrade significantly over time.

4. Resolution: Resolution is the smallest detectable increment in the measured quantity that an instrument can display or detect.

High-resolution instruments can measure finer details, which is critical for applications requiring precise measurements.

While resolution allows the detection of small changes, it does'nt necessarily imply high accuracy. An instrument may have high resolution but low accuracy if the readings deviate from the true value.

5. Range: The range is the span between the minimum and maximum values that an instrumant can measure accurately. If the measured value exceeds the instrument's range, it may lead to errors,damage, or misleading readings.

6. Response Time: Response time is the time an instrument takes to react to a change in the measured quantity and stabilize at the new reading.

In rapidly changing systems, a slow response time can lead to inaccurate readings or lag in measurement, making it unsuitable for real-time applications.

7. Precision: Precision refers to the ability of an instrument to consistently produce the same readings under identical conditions,even if those readings are not accurate.

While accuracy foccuses on how close the readings are to the true value, precision focuses on the repeatability of the readings. An instrument can be precise without being accurate and vice versa.

List of electrical instruments:

1. Ammeter
   

2. Voltmeter
   

3. Wattmeter
   

4. Transformer
   

5. Electric motor