Terms and Definitions in Instrumentation | ECE Board Exam

Instrumentation is essential for measuring, monitoring, and controlling physical and chemical processes across industries. It includes various tools and techniques vital for ensuring accuracy, efficiency, and safety, from temperature control in manufacturing to fluid flow monitoring in pipelines.

The following notes offer a concise reference of key terms and definitions in instrumentation crucial for understanding instrumentation. This resource is aimed at professionals, students, and enthusiasts seeking clarity in this specialized field.

List of Terms, Definitions, and Notes in 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 from 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 temperatures, 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

Ampere 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 moving coil 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 high-frequency 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 – an 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 arms 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, an 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, a 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

This compilation is a vital resource for anyone in instrumentation engineering, connecting basic and advanced concepts. It helps you troubleshoot complex systems and enhances your understanding of the field.