Multimeter

Hi friends! This time I am introducing one of the measurement devices i.e. Multimeter. This is the device which is used by people irrespective of age. Basically a Multimeter can be defined as an electronic measuring instrument which includes the ability to measure the voltage, current and resistance. Multimeter can also be called as VOM (Volt-Ohm-Meter). A multimeter can be used as the basic fault finding device for house hold electrical faults.

AVO meter

Multimeters were invented in the early 1920s by a British Post Office Engineer, Donald Macadie, Macadie invented an instrument which could measure amperes, volts, ohms, and hence it was named as "Avometer". The meter comprised of a moving coil meter, voltage and precision resistors, and switches and sockets to select the range. The first AVO was put on scale in 1923, and although it was initially a DC. Many of its features remained almost unaltered through to the last model.

There are two types of multimeter. They are:-

1. Analog multimeter (AMM).
2. Digital multimeter (DMM).

1. Analog multimeter:-

 Analog mutimeters are instruments that are used to measure electrical quantities such  as voltage current, resistance, frequency and signal power. Basic functionality includes measurement of potential in volts, resistance in ohms, and current in amps. These are used to find electronic and electrical problems. It contains advanced features like capacitor, diode testing and IC testing modes.. Analog multimeters can sometimes be difficult to read because they display data as needle moving along a scale this is the major disadvantage of it because when the operator reads the output then the reading will not be as accurate as of the reading in digital 

2. Digital multimeter (DMM):-

The digital multimeter is a versatile and most common digital measuring instrument that can be used for assembling, testing, and servicing laboratories. It displays the measurement of ac or dc voltages, dc or ac currents and resistance of discrete numerals. It is a handy and more accurate compared to analog meter.

These are instruments that are used to measure electrical quantities such as voltage, current, resistance, capacitance and time period. DMMs are generally bench top or hand held. Bench top models can also be portable by use of handles and wheels. Hand held multimeters are designed to be used while holding i.e. can be operated by with one hand. DMMs display information on a digital screen. Commonly they have between 3 and 6 digits, but some units come with larger screens that can display 7 or ore digits.

Advantages of DMM:-

DMM offer many advantages over analog multimeters, such as speed in reading, increased accuracy, better resolution, and capability of automated operation. DMM are available to read current, resistance, and AC or DC voltages directly without any parallax errors.

SL no	Parameters	Analog multimeter	Digital multimeter
1	Power supply	Not required	Required
2	Visual indication of changes in reading	Better	Not better
3	Effect of electric noise	Less	More
4	Isolation problems	Less	More
5	Accuracy	Less	High
6	Interface of the output with external equipment	Not possible	Possible
7	Construction	Simple	Complicated
8	Cost	Less	More
9	Size	Bigger	Smaller
10	Nature of output	Ambiguous many times	Unambiguous  reading

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Transducers

Hi friends! I think you all have heard the word “Transducer”. Now I just want to share some information about it.

Generally a Transducer can be defined as a device that transforms or converts one form of energy into another form i.e. non electrical quantity is converted into electrical quantity to measure, manipulate and control. In modern techniques, transducers are used to convert any form of energy into electrical energy. Many physical parameters such as heat, intensity, flow of rate can also be converted into electrical form by using Transducers.  Transducers can also be called as Sensor, Pickups, and Signal generators.

Characteristics of Transducers:-

The desirable characteristics of transducers are:-

1.     Faithful conversion of physical quantities to electrical form.

2.     Linearity between physical quantity and electrical analog.

3.     Small in size and less weight.

4.     High sensitivity.

5.     Good reliability.

6.     Low cost

7.     Withstands against extreme environmental conditions

Classifications of Transducers:-

Transducers may be classified on the basis of transduction form used, they are:-

1.     Primary and Secondary transducers: - The transducer which senses to a physical phenomenon and converts it into non electrical form is called as Primary transducer.

The transducer which senses to a physical quantity and converts into an analogous electrical quantity is called as Secondary transducer.

2.     Passive and active transducers: - The transducer which drives the power required for transduction from an auxiliary source is called as passive transducer.

Active Transducer

The transducer which does not require an auxiliary source to produce electrical output is called as an Active transducer.

3.     Analog and Digital transducers:-

Analog Transducer

    The transducer which converts the input quantity into an analog output as a continuous function of time is called an Analog transducer.

Digital Transducer

The transducer which converts input quantity into an electrical output in the form of pulse is called as a Digital transducer.

4.     Transducers and Inverse transducers: - The device which converts a non mechanical quantity into an electrical quantity is called as Transducers.

The device which converts an electrical quantity into a non electrical quantity is called as an inverse transducer.

Applications of Transducers:-

Some of the important applications are:-

·        Measurement of mass and volume.

·        Measurement of force and volume.

·        Measurement of stress and strain.

·        Measurement of speed and acceleration.

·        Measurement of temperature.

·        Measurement of pressure and differential pressure.

·        Measurement of flow and liquid level.

·        Measurement of moisture content and humidity.

·        Measurement of conductivity.

Transformers

Hi,friends here is some information about Transformers,

 Transformer is a static electrical device or stationary piece of apparatus, which transfers electrical power from one circuit to another, which are magnetically coupled together with or without change of voltage and without any change in power and frequency by the principle of mutual induction. As Transformer is a static device (there are no moving parts), hence there are no mechanical losses. Hence the efficiency is as high from 95%-98%. Maintenance of Transformer is easy since it has no slots, teeth and air gaps. In a Transformer electrical energy is generated, transmitted and distributed and used in the form of a.c. energy.

Basically transformer consists of two windings, such as primary winding and secondary windings. These windings are electrically separated but magnetically linked through a path of low reluctance.

The primary winding (coil) carries the source of alternating flux in the laminated core, most of this flux is linked to the secondary winding and produces a mutually induced e.m.f in it. If the secondary winding circuit is closed, a current flows in it, thus electric power is transferred from the primary to secondary coil.

Thus a transformer is a device that,

1.      Transfers electric power from one circuit to another without change in frequency.

2.      Works on the principal of electromagnetic induction.

3.      In which the two circuits are mutually connected each other.

First high efficiency transformer

Advantages of Transformers:-

• There is no tear and wear, so no friction loss because it is a static device.
• Maintenance cost.
• Transformers can be manufactured for very high voltages; therefore it is easy to insulate high voltage carrying stationary winding.
• The high voltage energy transmission is economical, that can be accomplished with the help of transformer.
• The efficiency of the transformer is very high.
• The high voltages can be transmitted with high precision by stepping down during transmission and stepping up during the reception with the help of the transformer.

Thermistors

Thermistors are ideal temperature transdusers. A thermistor can be defined as resistor made up of semiconductors having resistance that varies rapidly and predictably with temperature. The word thermistor is a portmanteau of Thermal & Resistors. 

In few cases the resistance of a thermistor may decrease upto 6 percent for 1⁰Celsius in temperature. Due to high sensitivity, thermistors are very useful for precision temperature measurement, control, and compensation. Thermistors are used in the temperature range of 100⁰  Celsius to 300⁰ Celsius. The resistance ranges from 0.552 to 72 Mega Ohms. Thermistors are made up of sintered mixture of metallic oxides such as cobalt, nickel, copper, manganese etc. they are available in the form of beads, rods or discs.Thermistors differ from Resistance Thermo Detectors (RTD) in that the material used in a thermistor is generally a ceramic or polymer, while RTDs use pure metals. The temperature response is also different.The characteristics of a Thermistor can be shown in the picture below:-

Classification of Thermistors:-

 Depending upon the sign of k the Thermistors can be classified into two types. They are:-

1. PTC Thermistors:-

 If k is positive, the resistance increase with the increasing temperature,& the device is called as Positive Temperature Coefficient(PTC) thermistor or Posistor. 

PTC Thermistor

2. NTC Thermistor:-

If k is negative,the resistance decreases with the increasing temperature,& the device is called as Negative Temperature Coefficient(NTC) thermistor.

NTC Thermistor

Thermistors have some advantages. They can be listed as below:-

1. PTC thermistors can be used as current limiting devices for circuit protection, as replacements for fuses.
2. PTC thermistors are used as timers in the degaussing coil circuit of most CRT displays & TVs.
3. NTC thermistors are used as resistance thermometers in low temperature measurements of the order of 10K.
4. NTC thermistors can be used as inrush current limiting devices in power supply.
5. NTC thermistors are regularly used in automotive applications.
6. NTC thermistors can be also used to monitor the temperature of an incubator.
7. Thermistors are commonly used in modern digital thermostats & to monitor the temperature of battery packs while charging.

Electronic Circuits

Electronic circuit is composed of individual electronic components such as resistors, transistors, capacitors, inductors, and diodes connected by conductive wires or traces through which electric current can flow .The combination of components and wires allow various operations such as amplification of signals, computations and transfer of data from one place to another. Circuits can be constructed from discrete components connected by individual pieces of wire, but now the interconnections are created by photolithographic techniques on a laminated substrate (a printed circuit board) and solder components to these interconnections to create a finished circuit.

Bread boards, perfboards or strip boards are common for testing designs. They allow the designer to make quick changes to the circuit.

An electronic circuit can be categorized as follows:-

1.      Analog circuit. 

2.      Digital circuit. and

3.      Mixed-signal circuit.

1.      Analog Electronic Circuit:-

Analog electronic circuits are those in which current or voltage may vary continuously with the time to correspond with the information being represented. Analog circuitry is constructed from two building blocks namely series and parallel circuits. In the series circuit, the current which is passed through all the series components will be same. In the parallel circuit, all the components are connected to the same voltage, and the current divides various components according to their resistance. The basic components of analog circuits are wires, resistors, capacitors, inductors, diodes and transistors (Recently memristors have been added to the list of available components). Analog circuits are very commonly represented in schematic diagrams, in which wires are shown as lines, and each component has unique symbol. When the size is comparable to wavelength of relevant signal frequency, a more sophisticated approach must be used. Wires are treated as transmission lines, with constant characteristic impedance, and the impedances at the beginning and end determine the transmitted and reflected waves on the line.

                                                                           

2. Digital Electronic Circuit:-

In digital electronic circuits, electric signals take on discrete values, to represent the information that is being processed. In the vast majority of cases binary coding is used. Digital circuits make extensive use of Transistors, interconnected to logic gates that provide the functions of Boolean logic. Transistors interconnected so as to provide positive feedback are used as latches and Flip-flops. Digital circuits therefore can provide both logic and memory, enabling them to perform arbitrary computational functions. (Memory based on Flip-flops is known as SRAM (Static Random Access Memory).

Memory based on storage of charge in a capacitor, DRAM (Dynamic Random Access Memory) is also widely used).

Digital circuits are very easy to design when compared to analog circuits for the same level of complexity, because each logic gate regenerates the binary signal, so the designer need not account for distortion, gain control, offset voltages, and other concerns faced in an analog design. As a consequence, extremely complex digital circuits, with billions of logic elements integrated on a single silicon chip, can be fabricated at low cost. Such digital integrated circuits are ubiquitous such as calculators, mobiles, computers...

Digital circuitry is used to create general purpose computing chips, such as microprocessors, & custom designed logic circuits, known as Application Specific Integrated circuits (APSIC’s). Field Programmable Gate Arrays (FPGA’s), chips with logic circuitry, whose configuration can be modified after fabrication, are also widely used in prototyping & development.

                               

3.      Mixed Signal Circuits:

Mixed signal or hybrid circuits contain both analog & digital circuits. Examples include comparators timers, PLLs, ADCs (analog to digital converters), & DACs (digital to analog converters).

Most modern Radio & Communication circuitry uses mixed signal circuits. For example in a receiver analog circuitry is used to amplify the frequency so that they reach the suitable state to be converted into digital values, after which further signal processing can be performed in digital domain.