What are measuring instruments?

The basic function of a measuring tool is to display, record, detect, control, and check the electrical unit system. In brief, it can be described that these gadgets are classified in two forms which are absolute form and secondary form.

Classification of electrical measuring instruments?

They are two types of measuring instruments:

• Absolute measuring instrument
• Secondary measuring Instrument 

Absolute instrument

This measuring instrument is used to measure the amount of electrical charge in terms of consistency and deflection. This instrument is divided into two parts: analog instrument and digital instrument. This type of instrument is not used for temperature measurement.

Example: Gravimeters (used to measure specific gravity) and tangent galvanometers are the best examples of absolute instruments.

Secondary instrument

This instrument uses its amount of deflection to measure or evaluate the electrical quantity.

This instrument is divided into two parts namely deflection instrument and null deflection instrument. This type of device is used for temperature measurement, current measurement, voltages measurement, etc.

Example: Ammeter, voltmeter, wattmeter, thermometer (used for temperature measurement), etc.

Classification based on the nature of operation

 These are four types of measuring instruments:

• Indicating instrument
• Recording instrument
• Integrating instrument
• Null deflection instrument 

Indicating instrument

This shows the value of an electrical and physical quantity at the time of measurement. This device gives the output which is the measurement value only when it is connected to the power supply. Otherwise, it reads zero.

 Example: Ammeter, voltmeter, wattmeter etc.

Recording instrument 

This measuring instrument is used to display and record the measurement value of the electrical quantities at the time of measurement.

Example: ECG, X-Rays, hand-held.

Integrating instrument

This is an analog integration tool which is used to measure the amount of power provided by a circuit in a given amount of time and does not depend on the total power used.

Example: Energy meter, Ampere-Hour meter are examples of integrating instruments.

What is a null deflection instrument?

A tool in which the zero or empty indicator determines the value of the quantity measured is called a blank type instrument. It uses a blank detector that shows an empty state where the measured quantity and the other quantity are same.

Example: Potentiometer is an example of the null deflection instrument.

Classification of the measuring instrument based on the electrical supply

They are two types of measuring instruments:

• Alternating current (AC) instrument
• Direct current (DC) instrument 

What is an alternating current (AC) instrument?

AC instrument is the measuring instrument which is connected with the AC supply. This instrument is divided into two-parts: Single-phase and three-phase AC instruments. For example, moving, induction, electrostatic, dynamometer, and electrostatic instrument.

What is a Direct current (DC) instrument?

DC instrument is the measuring instrument which is connected with the DC supply. For example: Permanent magnet moving coil instruments etc.

Classification of the instruments based on the effect

Based on the effect, the measuring instruments are classified into six types:

Moving coil Instruments

Moving coil instruments measure the standard value of current. On each movement of the moving coil, the FSD standard current value is marked along with the coil resistance so that the movement can be adjusted to measure other current ranges, voltages, and resistances.

Moving iron Instruments

The transfer iron tool is used to measure the float of modern or voltage is called the transferring iron tool. It works at the precept that the iron area close to the magnet draws in its direction—the pressure of appeal relief the photo-electricity of the magnetic field.

Induction instruments

An induction-type measuring instrument is a multiuse instrument.

Example: Ammeter, voltmeter, wattmeter etc.

Hotwire instruments

A hot wire instrument is an electrical measuring instrument in the cutting-edge to be measured exceeded through a skinny cord and reasons its temperature to rise. The temperature rises, proportional to the rectangular part of the cutting-edge, is the measurement through the enlargement of the cord.

Electrolytic instruments

Electrolytic instruments are devices for measuring electrical charge. A voltmeter and a Coulometer are the best examples of electrolytic instruments.

Electrostatic instruments

Electrostatic instruments measure power and also the high and low voltages of the given circuit.

Some main electrical instruments are as follows:

Ammeter

Ammeter is a measurement device used to measure electrical power in a circuit. A voltmeter is connected to an instrument to measure its voltage, whereas an ammeter is connected to a series by an instrument to measure its current. Moreover, a non-contact ammeter measures the direct current in a conductor in watts.

Voltmeter

A voltmeter is a measurement device used for measuring the electric potential difference in an electric powered circuit. It is connected in parallel. It commonly has an excessive resistance so that it takes negligible current from the circuit.

Ohmmeter

The ohmmeter is an electrical resistance measurement tool expressed in ohms. On simple ohmmeters, the resistance to be measured may be connected to the instrument in parallel or series.

Multimeter

A multimeter is an electronic measurement device used to measure voltage, current, and resistance circuits. By attaching two tracks to different parts of the electrical system, technicians can use multimeters to measure electrical and resistance levels or changes in electrical current.

Wattmeter

The measurement device used to measure the electrical power system in watts is known as an ammeter. They operate using three coils: two in a series with an electric load and one coil running in parallel. Series coils measure the current flow in a cycle whereas the parallel coil measures standard voltage.

Oscilloscope

The oscilloscope can be adjusted to determine the repeat indicator as a persistent waveform on display. Garage oscilloscopes can capture a single event and display it continuously, so consumers can check activities that seem too brief to view immediately in any other situation. Oscilloscopes are used in the field of science, medicine, engineering, automotive, and telecommunications. The standard reason for the installation of the oscilloscope is to refurbish digital systems and laboratory paintings. Special cause oscilloscopes can be used to analyze an automobile ignition gadget or to display the waveform of the heartbeat as an electrocardiogram, for instance.

 Some different types of measuring instruments:

• Actinometer
• Bolometer
• Colorimeter
• Declinometer
• Eudiometer
• Heliometer
• Tintometer

Context and Applications

This subject matter has tremendous importance for each undergraduate and graduate publication, mainly for:

• Bachelor of Technology in Electrical and Electronics Department
• Bachelor of Science in Physics
• Master of Science in Physics 

Common Mistakes

There are many instruments here, out of which it is not easy to choose the best, so choose the instrument with little attenuation.

Related Concepts

• Alternating Current
• Current and Electricity

Practice Problems

 Q1. Which one is the example of an absolute instrument?

1. Ammeter
2. Wattmeter
3. Tangent Galvanometer
4. Voltmeter

 Correct option: (d)

Explanation: Tangent galvanometer is the best example of an absolute instrument. This tool offers the value of the electrical quantity to be measured in terms of consistency and deflection.

 Q2. Which instrument measures the power and high and low voltage of the given circuit?

1. Wattmeter
2. Tangent Galvanometer
3. Voltmeter
4. Electrostatic Instruments

 Correct option: (d)

Explanation: Electrostatic instruments measure power and high and low voltage of the given circuit.

 Q3. Ammeter is connected in _________.

1. Only series
2. Only parallel
3. Series-parallel
4. Parallel-series

 Correct option: (a)

Explanation: As far as an Ammeter is concerned, it is connected in series for current measurement.

Q4. Ammeter provides a path for _____

1. Maximum voltage
2. Minimum voltage
3. Maximum current
4. Minimum current

 Correct option: (c)

Explanation: It is because an ammeter is used for current measuring. So, the ammeter provides a path for maximum current.

 Q5. Voltmeter provides a path for:

1. Maximum voltage
2. Minimum voltage
3. Maximum current
4. Minimum current

 Correct option: (d)

Explanation: It is because a voltmeter is used for voltage measurement, it has infinite resistance. So, the voltmeter meter provides a path for minimum current.