# Three Types of Analog Instruments

- Link: https://studyelectrical.com/2017/08/classification-of-analog-instruments.html
- Published: 2017-08-28T16:26:00+00:00

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.

## Types of Analog Instruments

Broadly, the analog instruments (and for that matter digital instruments) may be
classiﬁed according to the quantity they measure.

For example, an instrument meant for measurement of current is classiﬁed as an Ammeter
while an instrument that measures voltage is classiﬁed as a Voltmeter. Thus we have
wattmeters, power factor meters, frequency meters, etc…

Electrical instruments may also be classiﬁed according to the kind of current that
can be measured by them. Electrical instruments may be classiﬁed as instruments 
for:

 1. Direct Current (DC)
 2. Alternating Current (AC)
 3. Direct and Alternating Current (DC/AC)

Instruments depend for their operation on one of the many effects produced by current
and voltage and thus can be classiﬁed according to which of the effects is used 
for their working.

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The analog instruments are also classiﬁed as :

 1. Indicating instruments
 2. Recording instruments
 3. Integrating instruments

### 1. Indicating Instruments

Indicating instruments are those instruments that indicate the magnitude of a quantity
being measured. They generally make use of a dial and a pointer for this purpose.
Ordinary voltmeters, ammeters, and [wattmeters](https://studyelectrical.com/2019/01/three-phase-power-measurement-wattmeter-method.html)
belong to this category.

The analog indicating instruments may be divided into two groups :

 * Electromechanical instruments
 * Electronic instruments

Electronic instruments are constructed by the addition of electronic circuits to
electromagnetic indicators in order to increase the sensitivity and input impedance.

### 2. Recording Instruments

Recording Instruments give a continuous record of the quantity being measured over
a speciﬁed period.

The variations of the quantity being measured are recorded by a pen (attached to
the moving system of the instrument ; the moving system is operated by the quantity
being measured) on a sheet of paper carried by it rotating drum.

For example, we may have a recording voltmeter in a [substation ](https://studyelectrical.com/2019/04/electrical-substation-equipment-types-components-functions.html)
which keeps record of the variations of supply voltage during the day.

### 3. Integrating Instruments

Integrating Instruments totalize events over a speciﬁed period of time. The summation,
which they give is the product of time and an electrical quantity.

Ampere hour and watt hour (energy) meters are examples of this category.

The integration (summation value) is generally given by a register consisting of
a set of at pointers and dials.

The analog instruments may also be classiﬁed on the basis of method used for comparing
the unknown quantity (measurand) with the unit of measurement. The two categories
of instruments based upon this classiﬁcation are:

 1. Direct Measuring Instruments
 2. Comparison Instruments

#### a) Direct Measuring Instruments

Direct measuring instruments convert the energy of the measurand directly into energy
that actuates the instrument and the value of the unknown quantity is measured or
displayed or recorded directly.

The examples of this class of instruments are ammeters, voltmeters, wattmeters and
energy metres.

#### b) Comparison Instruments

Comparison instruments measure the unknown quantity by comparison with a standard.

Direct measuring instruments are the most commonly used in engineering practice 
because they are the most simple and inexpensive. Also their use makes the measurement
possible in the shortest time

The examples of comparison type instruments are DC and [AC bridges](https://www.allaboutcircuits.com/textbook/alternating-current/chpt-12/ac-bridge-circuits/).

Comparison instruments are used in cases where a higher accuracy of measurement 
is required.

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