Analog Instruments: 23 Important Facts You Should Know

Content: Analog Instruments

What is Analog Instruments ?

Analog Electronic Instruments

An analog instrument is one whose output or display is a continuous-time function. This instrument converts the input quantity into an analog O/Ps; having an infinite number of value. An analog instrument typically contains a pointer and a scaled calibrated dialler to show the output.

analog instrument
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Selecting factor of Analog Instrument:

Types of Analog Instruments

The analog instrument can also be of two types:

The direct measuring instrument is the instrument that converts the energy of the measuring quantity directly into energy that trigger the instrument, and the magnitude of quantity to be measured instantly.

A comparison instrument that compares the unknown quantity with a standard, when high accuracy is needed, is used.

One more classification of the analog instrument is

Analog Indicating Instruments

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It is indicating instrument that show the instantaneous value of the magnitude of the quantity to be calculated. The indicating instrument typically includes all null types of instrument and most passive ones. The most used is a dial and a pointer indication by the pointer moving over a calibrated dial.

The analog indicating instrument can be divided into two groups electromechanical instrument and electronic instrument.

Examples are ammeter and voltmeter.

Recording Instruments

The recording instrument gives a continuous record of the variation of the quantity being measured over a specific period. Although it is used to provide the overall performance of any instrument, it can provide data to evaluate the calibre and efficiency of the operating crews.

Types of Recording Instruments

 Analog Recording Instruments can be of three types:

What is Graphic recording instruments ?

Graphic recording instruments display and store records of the history of some physical event with pen and ink. They even may be varying voltage, current, pressure, etc. It mainly consists of a chart for storing and displaying recorded data. This stylus moves on paper with proper relationship and an internal connection which connects the stylus to the information source.

Integrating Instruments

An integrating instrument is an instrument to find the sum of measurements over a specific period the summation in which this provide as product of time and the measured quantity.

Principle of Operation of Analog Instruments

Operating Torques in Analogue Instruments are

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Operating force or torque:

Deflecting Force or torque: It is a force or torque which reflects the pointer from its 0th position of calibrated scale according to the magnitude of the quantity passing thru the device.

Controlling Force or torque:  which control the movement of the pointer on a required scale. It is needed to bring the pointer to the 0th point at if no deflecting force. To produce an equal and opposite force to the deflecting Force to make the pointer steady in the absence of controlling Force pointer may swing away from the final study position for any magnitude. Controlling torque can be produced by Spring control gravity control.

Damping force or Torque: This used to prevent from the vibration for oscillation of the pointer on a particular range of scale; It is required to bring back the pointer at rest. Damping force can be established by air friction fluid friction Eddy current damping.

Magnetic Effect

In a uniform magnetic field, a current-carrying conductor is situated, which result in a disturbance in the magnetic field, impacts force (F). The direction of Force will be the opposite direction of the current and coil conductor generate magnetic field act as magnetic material.

Force of attraction or repulsion 

When a piece of soft iron that is not magnetized previously, kept near the end of the coil. When current flow through the coil, the soft iron becomes magnetised and gets pulled inside the coil. The Force of attraction is proportional to the field strength inside the coil and proportional to the current strength; utilized in attractive moving iron (M.I) instrument.

If two soft iron pieces are situated near the coil, become magnetized, and then there will be repulsion force; utilized in repulsive moving iron (M.I) instrument.

The Force between a current-carrying coil and a permanent magnet is used in a permanent magnet moving coil instrument, and Force among 2 current-carrying coil is utilized as the key principle in dynamo meter type of instrument.

Thermal Effect

The current to be measured is passed through a heating element whose temperature increases with the increase in current and temp change is converted into an EMF by a Thermo-couple. The thermocouple is designed with two dissimilar electric conductors joined together at the end of each other to form a close loop, the point the dissimilar metal meets is the junction. If both the junction is maintained at a different temperature, a current will flow through the loop.

Electrostatic Effect

The electrostatic effect is the attractive force among 2 or many electrically charged elements between which a potential diff is preserved. That force results in to increase in deflecting torque. The electrostatic effect is the basic principle of an electrostatic instrument known as an electrometer voltmeter, an example of an electrostatic instrument.

Advantages of electrostatic instrument:

Disadvantages of electrostatic instruments:

Induction Effect

Induction effect when a non-magnetic conducting disc or drum is placed in the magnetic field which is excited by alternating currents, EMF will be induced in the drum or disc. If the closed path is provided, then EMF will cause a current flow to the drum or disc. the produced force in the interaction of the induced current and the magnetic field will cause the disc or drum to move this effect is used in energy meter.

Advantages of induction instruments:

Disadvantages of induction instrument:

Errors in the induction instrument are due to frequency variation or temperature variation.

Hall Effect

This is the formation of potential difference across a conducting material having electrical current exist in a cross magnetic field.

The magnitude of the potential drop depends on the current flux density, and the internal property of the conductor is called the hall effect coefficient. The emf produced in this phenomenon is so small for measurement, which may require amplification. Hall effect instruments are used for sensing current or in magnetic measurement. Examples are flux meter ammeter Poynting vector watt-meter. Hall effect instruments convert the magnetic field into electric quantity, which can be easily be measured.

Advantages of hall effects:

Disadvantages of hall effects:

What are the advantages of digital instruments over analog instruments?

Advantages and Disadvantages of Analog and Digital Instruments.

Advantages of Digital Instruments over Analog :

Disadvantages of Digital Instrumentation:

Advantages of Analog Instrumentation:

Disadvantages of Analog Instrumentation:

Analog Devices Instrumentation Amplifier

Analog devices instrumentation amplifier when the output of any instrument is low or needed any amplification for further processing the input to the instrument amplifier is the output from the centre of the transducer used to amplify, reject noise and signal interference. An instrumentation amplifier is a differential amplifier, and an analog device instrumentation amplifier is a precision block with a differential input and output. This device amplifies the differences between the two input signal voltages while rejecting signals common to both inputs.

Analog Instrument Cluster |Instrument Cluster Analog

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An analog instrument cluster is a group of different analog instruments, and it can include different analog metres and gauges to provide the required measurement. These clusters are used for safety order requirement mainly used in automobiles, aircraft etc. this cluster use different m for measuring required information, for example, in automobile, speed, fuel level, charge level, etc.

What is the difference between Digital and Analog Measuring Instruments ?

Comparison between Analog and Digital instruments

Analog InstrumentDigital Instrument
Low PrecisionHigh Precision
High power RequirementLow Power Requirement
Highly SensitiveLess Sensitive
Less ResolutionHigh Resolution
Not compatible directly with a computer, microprocessor or microcontrollercompatible directly with a computer, microprocessor or microcontroller
More FlexibleLimited flexibility
Parallax error during reading result is possibleNo reading error due to digital display
Can get easily affected by noiseHigh noise immune
Easily portableNot easily portable
Continuous convenient for readoutConvenience in readout

Electronic Test Instruments Analog and Digital Measurements

Electronic test instrument testing instruments are used to detect a fault in operation, such as voltmeter, ammeter, ohmmeter, multimeter, frequency counter, oscilloscope or LCR meter, etc.

The testing instrument is the key to any electronic design production and maintenance. It can be an analog or digital instrument used to generate a signal and capture the response from the device Under test.

Analog Aircraft Instruments

Following are the analog instruments which are used in aircraft:

The altimeter is a device used to measure an object’s altitude relative to a fixed level. It has two types of pressure altimeter and radio altimeter and study of altitude is known as altimetry. 

Image Credit:“Aircraft altimeter” by cambridgebayweather is licensed under CC BY-SA 2.0

A pressure altimeter calculate altitude as per atmospheric pressure. With the increase in altitude, the pressure reduces. Radio altimeter determines the height of any subject by sending a signal to the ground and measure the attitude based on the time required for the radio wave signal to travel. Altimeter having mechanical internal aneroid capsule have an analog display.

Air speed indicator is used to measure the aircraft’s speed; It uses a pitot tube which is U shaped with two openings .airspeed indicator traditionally is a mechanical analog instrument.

Magnetic compass and instrument for determining direction by using a magnetic element which shows the direction of the horizontal component of the magnetic field of the earth

The tachometer is a device that indicates the rate of rotating an object or engine shaft; it includes the instantaneous value of speed in RPM. It is composed of a tile and little to indicate the immediate reading.

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Analog Polygraph Instrument

An analog polygraph instrument is commonly known as the Lie Detector instrument, measuring at least three physiological responses like blood pressure, pulse respiration, and skin connectivity.

It can consist of pneumographs to record respiratory activity, blood pressure cliff to record cardiovascular activity,  and galvanometer activity sensor, plethysmograph, etc. The analog polygraph needles draw the line on a paper to record and show the output. These lines represent the level of stress which can affect if the person is telling a lie.

Analog Weather Station Instruments

Analog weather instruments:

The thermometer is used to measure the temperature of the environment. There are many types of thermometers. One of the most used thermometers is a thermistor designed with metal oxide and has a high-temperature Coefficient, so with the temperature change, the resistance shift occurs.

Thermistor mainly has negative temperature Coefficient. Although the increase in temperature resistance decreases, it is very sensitive to temperature change, making thermistors useful for Precision temperature measurement.

A barometer is an instrument uses to measure the pressure of the atmosphere because atmospheric pressure varies with altitude. A simple barometer is a mercury-in-glass barometer unit of measurement. The atmosphere or bar Mercury glass parameter is closed at the top and open at the bottom. Thus, there is a pool of Mercury. 

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The aneroid barometer is a non-liquid barometer that is widely in use. It is small and uses an evacuated capsule as a sensing element, the flexible walled evacuated capsule. The flex with the change in atmospheric pressure the deflection is coupled mechanically to an indicating needle.

A hygrometer is a device that indirectly measures humidity by sensing a change in physical or electrical property in materials, which causes due to moisture content. There are different types of hygrometers for humidity measurement. In mechanical hygrometer measures humidity with the change in length of the hair element by the contraction and expansion of the hair element. 

A rain gauge is a device that is used to measure rain in a certain period. It usually measured rainfall in millimetres. There are different types of rain gauges. The most precise one is the ground level gauge, where the orifice of the gauge is placed with the ground level surface and surrounded by an anti-splash grid.

Anemometer is a device that measures the rate of flow, which can be used for measuring airflow. A hot wire anemometer is widely used for measuring the mean and fluctuating velocity of fluid flows. Steam of air will cool down a heated object is the principle of hot wire anemometer a heated wire is placed in the airflow.

Pyranometer is an instrument that is used to measure solar radiation. It is operated on the measurement of the temperature difference between a bright surface and a dark surface. There are different types of pyranometers, such as thermopile pyranometers, photovoltaic pyranometers, etc.

Examples of Analog Instruments

Uncertainty for Analog Instruments

Uncertainty of analogue resolution uncertainty is one of the problems in analogue instruments. It considers the limitation of measurement. The Precision accuracy of a measurement is limited by the resolution of the instrument for an analog instrument with gradual scaling sometimes causes parallax error when taking a reading from different view position will give different reading leads to an error which creates uncertainty in measurement.

Frequently Asked Questions.

What are absolute and secondary instruments?

Absolute Instrument:

These instrument provides the magnitude of the measuring quantity in terms of physical instrumental constant. 

Secondary instrument:

These instrument convert the analog o/ps  of the primary/absolute instrument into an electrical signal. These instruments are required to be calibrated by comparison with an absolute instrument that has already been calibrated.

Analog Instruments are preferred for ?

Error in Analog Instruments ?

three different types of error that happen in any instrument:

  •  Instrumental Errors: These errors are caused by miss-use of the instrument, loading effect, ageing or inherent shortcomings.
  •  Environmental Errors: These errors are caused by external condition of the instrument, hence errors are may affect by surroundings temp, pressure, humidity, dust, etc.
  •  Observational Errors: these errors occur due to human observational factors. There can be reading parallax error in analog instruments, which is an observational error. Different moving parts in an analog instrument can produce an error when friction between two components is created, an instrumental error. Ageing of the instrument can produce an error is also an instrumental error. 

What are some examples of common Analog Devices ?

What are the Comparative Advantages and Disadvantages of Digital and Analogue Multimeters ?

What is a Micrometer ?

Micrometer is also known as micrometer caliper or micrometer screw gauge. It is an instrument for measuring linear(small) distance precisely, such as diameter, length, thickness, etc. 

How does an Ohm Meter Measure Resistance ?

Ohm meter can not measure resistance directly but can measure the power through a circuit. Any known voltage is connected to a component whose resistance is measured, where resistance is unknown by measuring the current through the measuring component. Through Ohm’s Law relationship between voltage current and resistance is known. Therefore, we can calculate the value of the unknown resistance by finding current through the circuit as the voltage is known.

Is Wifi a Digital Signal or an Analog?

The wifi signal is both analog and digital and for that ,  ADC  and DAC and modulation of the signal takes place as requirements.

What is Wattmeter and its construction?

A wattmeter is an instrument that measures the electrical energy of a circuit. The unit of measurement is in watts. It can be an electro-dynamometer or induction watt meter. It can be constructed with a current coil and voltage coil, the current coil is adjoining in series connection, and the voltage coil is connected by parallel connection. The needle which moves on the calibrated scale is connected to the voltage coil. The voltage coil is a moving coil, whereas the current coil is immobile.

How to find Multiplication factor for Wattmeter ?

Multiplication factor = (voltage range X current range X power factor)/(range of wattmeter)

Is there anything that an Analog Multimeter does better than Digital one If so Why ?

Analog multimeters are suitable for measuring fluctuating values better than that of digital multimeters, because sudden fluctuation can not be precisely represented by digital multimeters. While analog multimeter has changing display which can accurately show the sudden fluctuations, it may not provide exact reading but it will provide instantaneous and rough measurement.

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