INSTRUMENTATION Accuracy – the degree of exactness of

measurement when

compared to the expected value of the

variable being measured

Measurement – the art, or process of

determining the existence

of knowing the magnitude of something,

directly or indirectly in

terms of a recognized standard

Test – a procedure, or sequence of

operations for determining

whether a component or equipment is

functioning or working

normally

In measurement, accuracy is the degree of

exactness compared

to the expected value of the variable being

measured

A measure of consistency or repeatability of

measurements is

called precision

Precision is also known as reproducibility

In measurements, the sum of a set of

numbers divided by the total

number of pieces of data in the given set is

called arithmetic

mean

Error – the deviation of a reading form the

expected value

Instrument errors – errors due to frictions

of the meter

movement, incorrect spring tension,

improper calibration or faulty

instruments

When an instrument is subjected to harsh

environments such as

high temperature, strong magnetic,

electrostatic, or

electromagnetic field, it may have a

detrimental effects and cause

errors known as environmental errors

Observation errors – errors introduced by

the observer or user

Parallax error – errors in analog meter

reading due to your

physical position with respect to the meter

scale

Deviation – the difference between any

number within the set of

numbers and the arithmetic mean of that set

of numbers

Standard instrument/device – an instrument

or device having

recognized permanent or stable value that is

used as a reference

Resolution – the smallest change in a

measured variable to which

an instrument will respond

Instrument – a device or mechanism used to

determine the value

of a quantity under observation

Amepe is the basic unit for measuring

current flow

An instrument used to detect and measure

the presence of

electrical current is generally called

galvanometer

D’ Arsonoval is the common type of meter

moving

D’ Arsonoval meter movement – a

permanent-magnet movingcoil

instrument

Moving-iron instrument – an instrument

which depends on

current in one or more fixed-coils acting on

one of more pieces of

soft iron, at least one of which is movable

Moving-magnet instrument – depends on

the action of a

movable permanent magnet, in aligning

itself in the resultant field,

produced either by a fixed permanent

magnet and an adjacent coil

or coils carrying current, or by two or more

current-carrying coils

whose axes are displaced by a fixed angle

Thermocouple ammeter is mostly used in

measuring highfrequency

currents

Measurement of high dc-voltages is usually

done by using electrostatic

Electrostatic – measuring instrument that

can be used only to measure voltages

Pyrometer – this instrument measures

temperatures by electric

means, especially temperatures beyond the

range of mercury

thermometers

Pyranometer – this instrument refers to that

one, which measures

the intensity of the radiation, received from

any portion of the sky

Infinity is the normal indication on a

megger (megaohmmeter)

when checking insulation

Megaohmmeter, megger – Resistance

measuring instrument

particularly used in determining the

insulation resistance

Wattmeter – an electrodynamic meter used

to measure power

Dynamometer – a device used to

mechanically measure the

output power of a motor

Electrodynamometer – an indicating

instrument whose movable

coils rotate between two stationary coils,

usually used as

wattmeter

Dynamometers are mostly used as

wattmeter

Air friction damping method is generally

used in dynamometers

Wattmeter dynamometer instrument has a

uniform scale

For a dynamometer to be able to measure

high current, a current

transformer should be used

Error in voltmeter reading is due to loading

Error in ammeter reading is due to insertion

An ohmmeter type of meter requires its own

power source

Error in ohmmeter reading is due to battery

aging

Decreasing the value of the shunt resistor of

an ammeter, its

current measuring capability increases

Increasing the value of the series resistor of

a voltmeter, its voltage

measuring capability increases

Clamp probe – a device that is used to

measure current without

opening the circuit

Clamp-meter ammeter has no insertion error

To prevent damage of the multirange

ammeter during selection, an

Ayrton shunt should be used

For the greatest accuracy, the input

impedance of a VOM should be

as large as possible

Voltage measurement in a high impedance

circuit requires a

voltmeter with high input impedance

In order to make an accurate measurement

as possible, the

internal resistance of a voltmeter must be as

high as possible

The purpose of the rheostat in ohmmeter is

to compensate the

aging battery of the meter

The zero-adjust control in an analog type

ohmmeter is used to

compensate for the differing internal

battery voltage

The scale of a hot wire instrument is a

squared function

Moving iron instruments have a scale

function that is squared

To increase the measuring capability of a

moving-iron ac ammeter,

a different number of turns of operating

coil should be used

PMMC electrical instrument is the most

sensitive

Basically, a PMMC instrument can be used

only in dc

measurement

Spring action – controlling torque in

PMMC

Eddy current damping method is used in

induction type

ammeter

Induction type instruments are mostly used

as watt-hour meter

In indicating instruments, the controlling

torque increases if the

deflection becomes greater

Controlling torque and deflecting torque

are forces that are

acting on the pointer of an indicating

instrument as it rest on its

final deflected position

Controlling, damping, and deflecting

torques are the forces

acting on the pointer of an indicating

instrument when it is in

motion

Aluminum – material that is mostly used as

a pointer in indicating

instrument

A Kelvin electrostatic voltmeter uses fluid

friction method of

damping

Shunts in meters should have a very small

temperature

coefficient of resistance

In a moving coil ammeter, a swamping

resistor is connected in

series with the coil to compensate for

temperature variations

We use the dynamometer in dc and ac

Electrostatic instrument – meter that

depends for its operation

on the forces of attraction and repulsion

between electrically

charged bodies

Induction instrument – instrument that

depends for its operation

on the reaction between magnetic flux set up

by currents in fixed

windings and other currents set up by

electromagnetic induction in

movable conduction parts

Permanent-magnet moving-coil instrument

– a meter that for

its operation, it depends on a movable iron

vane which aligns itself

in the resultant field of a permanent magnet

and an adjacent

current carrying coil

Vane-type instrument uses the force of

repulsion between fixed

and movable magnetized iron vanes, or the

force between a coil

and a pivoted vane-shaped piece of soft iron

to move the indicating

pointer

Kelvin voltmeter – its an electrostatic

voltmeter in which an

assembly of figure 8 shaped metal plates

rotates between the

plates of a stationary assembly when a

voltage is applied between

the assemblies. The length of the arc of

rotation is proportional to

the electrostatic attraction and thus, to the

applied voltage

Magnetometer is an instrument used for

measuring the strength

and direction of magnetic field

Varmeter and reactive volt-ampere meter

are the instrument

used for measuring reactive power in vars

Bridge is a circuit that has four or more

arms, by means of which

one or more of the electrical constants of an

unknown component

may be measured

Resistance bridge, wheatstone bridge – a

four-arm bridge. All

arms of which are predominantly resistive;

used for measuring

resistance

Varley loop – this is a method of using a

Wheatstone bridge to

determine the distance from the test point to

a fault in a telephone

or telegraph line or cable

Maxwell bridge – this refers to a four-arm

ac bridge used for

measuring inductance against a standard

capacitance

Hay bridge – refers to an ac bridge for

measuring the inductance

and Q of an inductor in terms of resistance,

frequency and a

standard capacitance

Kelvin double bridge – this is a special

bridge for measuring very

low resistance (0.1 or less). The arrangement

of the bridge reduces

the effects of contact resistance, which

causes significant error

when such low resistance are connected to

conventional resistance

bridges

Schering bridge – a type of four-arm

capacitance bridge in which

the unknown capacitance is compared with a

standard

capacitance. This bridge is frequently

employed in testing

electrolytic capacitors, to which a dc

polarizing voltage is applied

during the measurement

Wein bridge – a frequency-sensitive bridge

in which two adjacent

arms are resistances and the other two arm

are RC combinations

When the capacitors of a Wien bridge are

replaced by inductors,

the bridge becomes Wein inductance bridge

Slide-wire bridge – a simplified version of

the Wheatstone bridge

wherein, two of the ratio arms are replaced

by a 100 cm long

Manganin of uniform cross-sections and

provided with a slider

Radio-frequency bridge – bridge used to

measure both inductive

and capacitive impedances at higher

frequencies

Balance bridge – a bridge wherein all legs

are electrically

identical

Spectrum analyzer is an electronic

instrument capable of

showing on screen and maybe on print,

relative spacing of

transmitter carriers, their sidebands and

harmonics

Spectrum analyzer – an instrument capable

of displaying

simultaneously the amplitude of signals

having different

frequencies

A spectrum analyzer is a real-time analyzer

Indications of spectrum analyzer is

presented by means of a CRT

Oscilloscope – an electronic measuring

device that provide

instantaneous visual indication of voltage

excursions

Oscilloscope – an instrument that is capable

of displaying

waveforms by means of a fluorescence in a

CRT

Storage oscilloscope – types of

oscilloscopes that are able to

retain the display for a longer period for

analysis. The display is

retained by the use of flood gun

Sampling oscilloscope uses sampling

technique in processing

signals having frequencies beyond its

normal capabilities

Generally, oscilloscope uses electrostatic

deflection

Signal generators – a device or instrument,

which delivers

signals of precise frequency and amplitude,

usually over a wide

range

The two most common audio oscillators are

Wein bridge and

phase-shift

The two most popular RF oscillators are

Colpitts and Hartley

Noise generator – a device or instrument

able to generate noise

with accurate voltage for test purposes

You need a noise generator when evaluating

noise

characteristics of an amplifier

In RF or microwave system, reflectometer is

used to measure the

incidental and reflected signals

Reflectometer – a type of photometer used

to measure reflection

Dip meter – a tunable RF instrument, which,

by means of a sharp

dip of an indicating meter, indicates

resonance with an external

circuit under test

Grid-dip meter – a type of dip meter

employing a vacuum tube

oscillator, whose indicating dc

microammeter is in the grid circuit

In meter movement, you prevent the meter

from oscillation and

overswing by damping

When the meter is insufficiently damped, it

is considered as

underdamped

A meter when overdamped will become

insensitive to small signals

Test and Measurement An ammeter is an indicating instrument

As the deflection of the moving system

increases, the controlling

torque in an indicating instrument increases

D’Arsonval is the best type of meter

movement

Wattmeter dynamometer type has uniform

scale

When both deflecting and controlling torque

act, the pointer of an

indicating instrument comes to rest

The output voltage of a thermocouple

increases with

temperature

Analog instrument – an instrument in which

the magnitude of the

measured quantity is indicated by means of

a pointer

If the pointer of an indicating instrument is

in motion, damping

and controlling torques oppose the

deflecting torque

Electrical currents can be induced with a

coil and a magnet by

moving either the magnet or the coil

The fuse should never be replaced with a

higher rated unit

The pointer of an indicating instrument is

generally made of

aluminum

The time interval that a waveform is high (or

low) is the pulse

width of the signal

A Wheatstone bridge is balanced if the ratio

of resistors on one

side of the bridge equals the ratio of

resistors on the other

side

The pointer of an indicating instrument is in

the final deflected

position, the damping torque is zero

Deflecting force – a moving system force in

analog instruments

which causes the moving system to deflect

from its zero position

Controlling force – a moving system force

in analog instruments

which ensures that the deflection of the

pointer for a given value of

measured quantity always has the same

value

All voltmeters except electrostatic is

operated by the passage of

current

Disc is made of conductor and non-

magnetic material in eddy

current damping

The time interval between pulses is called

pulse delay

An oscilloscope provides easy measurement

of peak to peak

values

Fuse is an element in electronics which

serves as a protection

against overlead

Diode sensor provides a dc voltage

approximately 1V to 10 mW

Hot-wire instrument has a squared scale

For time measurements, horizontal scale of

the scope is used

Fluid friction damping is employed in

Kelvin electrostatic

voltmeter

Current range extension in moving coil

instruments can be

achieved by placing a low resistance

resistor in shunt with the

instrument

Permanent-magnet moving coil instrument

can be used in dc work

only

Control grid CRT element provides for

control of the number of

electrons passing farther into the tube

Orthogonal nulling refers to garaging the

two adjustments of an

AC bridge together in such a way that

changing one adjustment

changes the other in a special way, but

changing the second

adjustment does not change the first

When the vertical input is 0V, the electron

beam may be positioned

at the vertical center of the screen

The reason why the scale of a permanent-

magnet moving coli

instrument is uniform is because it is spring

controlled

Thermal converters – a sensing element that

provides a dc

voltage less than 10mV with typical power

range of 0.1 to 100 mW

Tank circuit frequency can be measured by

Grid-dip meter

Shunts are generally made of Manganin

material

1 μA meter is the most sensitive

A dynamometer instrument is mainly used

as a wattmeter

Dynamometer movement is the most

expensive

Attraction and repulsion instrument are

considered as movingiron

instruments

In wheatstone bridge, bridge balance is a

condition where there is

no current that flows through the load

The temperature coefficient of resistance of

the shunt material is

negligible

In VTVMS, zero adjust is used to balance

both halves of the

difference amplifier or cathode-coupled

amplifier

In an oscilloscope, intensity control adjusts

the brightness of the

spot by changing the voltage on the control

grid

Damping force – a force in analog

instrument which quickly

brings the moving system to rest in its final

position

A small swamping resistance is connected in

series with operating

coil of a moving coil ammeter in order to

compensate for the

effects of temperature variation

The typical power range of diode sensor is

0.1 nW to 10 mW

A milliameter operates on the magnetic

attraction-repulsion

principles

Wheatstone bridge – a dc bridge widely

used for the accurate

measurement of resistance

Potentiometer bridge is a dc bridge that is

very useful for

making extremely accurate voltage

measurements

Majority of the analog measuring instrument

utilizes magnetic

effect

Multimeter typically provides measurement

of rms values (for a

sinusoidal waveform)

Dynamometer type instrument can be used

for both dc and ac

works

Permanent-magnet moving coil is an

instrument in which

springs provide the controlling torque as

well as serve to lead

current into and out of the operating coil

In VTVMS, sensitivity refers to the smallest

signal that can be

reliably measured

The frequency of rotation in some rotating

machinery can be

measured by a Spectral meter

An instrument used for observing voltage

and current waveforms is

the oscilloscope

An electrostatic force does not act on the

moving systems of

analog instrument

When current through the operating coil of a

moving-iron

instrument is tripled the operating force

becomes nine times

50 mA is the typical full-scale deflection

current of a moving coil

instrument

Ammeter – an instrument used for

measuring the amount of

current flowing in a circuit

DMM – a type of meter that gives a precise

reading of voltage,

current or resistance where there is the

generation of samples at

the input and then feeds it to a digital read-

out

50 mV is the typical full-scale voltage across

a moving coil

voltmeter

The period of a repetitive signal is one cycle

of the waveform

Cathode – an element of a CRT that releases

electrons when

heated indirectly by a filament

Moving-iron instrument has a squared scale

A pattern displayed by oscilloscope which

has a steady

characteristic is called Lissajous

Changing the number of turns of operating

coil extends the

range of a moving-iron ac ammter

Sawtooth generator is not a basic part of a

CRT

For amplitude measurements, vertical scale

is calibrated in either

volts per centimeter (V/cm), or millivolts

per centimeter (mV/cm)

Thermocouple ammter is used to measure

high-frequency

currents

Electrostatic is used for measuring high

direct voltage

A common technique for measuring power

at high frequency is to

employ a sensing element that converts the

RF power to a

measurable dc or low-frequency signal

The CRT provides the visual displaying

showing the form of the

signal applied as a waveform on the front

screen of a cathode ray

oscilloscope.

Electrostatic instruments are exclusively

used as voltmeters

0.1 μW to100 μW is the typical power range

of thermocouple

sensors

An electric pyrometer is an instrument used

to measure high

temperature

Permanent-magnet moving coil is the most

sensitive

Induction watt-hour meter is the most

commonly used induction

type instrument

An integrating type of instrument is the

watt-hour meter

Indicating instrument is assumed to be most

accurate at half of

full part of the scale

On a simple ohmmeter, the 0 ohm mark is

located at far right of

the scale

One of the basic functions of electronic

circuit is the generation

and manipulation of electronic waveshapes

Cathode ray oscilloscope (CRO) provides a

visual presentation

of any waveform applied to the input

terminals

The interval of a pulse from start to end is

the period of the pulse

Cathode ray tube (CRT) is considered as the

“heart” of the

cathode ray oscilloscope

Phosphor – a material that glows when

struck by the energetic

electrons in a CRT

Thermiston sensor provides a change of

resistance with typical

power range of 1 μW to 10 mW and with

maximum frequency

greater than 100 GHz

Most AC voltmeters have an rms scale

which is valid only if the

input signal being measured is a sinusoidal

signal

Wheatstone bridge measures dc resistance

Hay bridge is used to measure high-Q

inductors (Q>10)

Maxwell bridge measures an unknown

inductance in terms of

known capacitance

Maxwell bridge is used for measuring

medium Q coils (1<Q<10)

Wien bridge has a series RC combination in

one arm and a

parallel RC combination in the adjoining

arm and used as a notch

filter in harmonic distortion analyzer

Sensitivity of a voltmeter is express in

ohm/volt

The smallest change in applied stimulus that

will indicate a

detectable change in deflection in an

indicating instrument is called

resolution

Insulation material is measured by Megger