What is a meter?

What is a meter?

Most modern meters are "digital" in design, meaning that their readable display is in the form of numerical digits. Older designs of meters are mechanical in nature, using some kind of pointer device to show quantity of measurement. In either case, the principles applied in adapting a display unit to the measurement of (relatively) large quantities of voltage, current, or resistance are the same.A meter is any device built to accurately detect and display an electrical quantity in a form readable by a human being. Usually this "readable form" is visual: motion of a pointer on a scale, a series of lights arranged to form a "bargraph," or some sort of display composed of numerical figures. In the analysis and testing of circuits, there are meters designed to accurately measure the basic quantities of voltage, current, and resistance. There are many other types of meters as well, but this chapter primarily covers the design and operation of the basic three.

The display mechanism of a meter is often referred to as a movement, borrowing from its mechanical nature to move a pointer along a scale so that a measured value may be read. Though modern digital meters have no moving parts, the term "movement" may be applied to the same basic device performing the display function.

The design of digital "movements" is beyond the scope of this chapter, but mechanical meter movement designs are very understandable. Most mechanical movements are based on the principle of electromagnetism: that electric current through a conductor produces a magnetic field perpendicular to the axis of electron flow. The greater the electric current, the stronger the magnetic field produced. If the magnetic field formed by the conductor is allowed to interact with another magnetic field, a physical force will be generated between the two sources of fields. If one of these sources is free to move with respect to the other, it will do so as current is conducted through the wire, the motion (usually against the resistance of a spring) being proportional to strength of current.

The first meter movements built were known as galvanometers, and were usually designed with maximum sensitivity in mind. A very simple galvanometer may be made from a magnetized needle (such as the needle from a magnetic compass) suspended from a string, and positioned within a coil of wire. Current through the wire coil will produce a magnetic field which will deflect the needle from pointing in the direction of earth's magnetic field. An antique string galvanometer is shown in the following photograph:

Such instruments were useful in their time, but have little place in the modern world except as proof-of-concept and elementary experimental devices. They are highly susceptible to motion of any kind, and to any disturbances in the natural magnetic field of the earth. Now, the term "galvanometer" usually refers to any design of electromagnetic meter movement built for exceptional sensitivity, and not necessarily a crude device such as that shown in the photograph. Practical electromagnetic meter movements can be made now where a pivoting wire coil is suspended in a strong magnetic field, shielded from the majority of outside influences. Such an instrument design is generally known as a permanent-magnet, moving coil, or PMMC movement:

In the picture above, the meter movement "needle" is shown pointing somewhere around 35 percent of full-scale, zero being full to the left of the arc and full-scale being completely to the right of the arc. An increase in measured current will drive the needle to point further to the right and a decrease will cause the needle to drop back down toward its resting point on the left. The arc on the meter display is labeled with numbers to indicate the value of the quantity being measured, whatever that quantity is. In other words, if it takes 50 microamps of current to drive the needle fully to the right (making this a "50 μA full-scale movement"), the scale would have 0 μA written at the very left end and 50 μA at the very right, 25 μA being marked in the middle of the scale. In all likelihood, the scale would be divided into much smaller graduating marks, probably every 5 or 1 μA, to allow whoever is viewing the movement to infer a more precise reading from the needle's position.

The meter movement will have a pair of metal connection terminals on the back for current to enter and exit. Most meter movements are polarity-sensitive, one direction of current driving the needle to the right and the other driving it to the left. Some meter movements have a needle that is spring-centered in the middle of the scale sweep instead of to the left, thus enabling measurements of either polarity:

Common polarity-sensitive movements include the D'Arsonval and Weston designs, both PMMC-type instruments. Current in one direction through the wire will produce a clockwise torque on the needle mechanism, while current the other direction will produce a counter-clockwise torque.

Some meter movements are polarity-insensitive, relying on the attraction of an unmagnetized, movable iron vane toward a stationary, current-carrying wire to deflect the needle. Such meters are ideally suited for the measurement of alternating current (AC). A polarity-sensitive movement would just vibrate back and forth uselessly if connected to a source of AC.

While most mechanical meter movements are based on electromagnetism (electron flow through a conductor creating a perpendicular magnetic field), a few are based on electrostatics: that is, the attractive or repulsive force generated by electric charges across space. This is the same phenomenon exhibited by certain materials (such as wax and wool) when rubbed together. If a voltage is applied between two conductive surfaces across an air gap, there will be a physical force attracting the two surfaces together capable of moving some kind of indicating mechanism. That physical force is directly proportional to the voltage applied between the plates, and inversely proportional to the square of the distance between the plates. The force is also irrespective of polarity, making this a polarity-insensitive type of meter movement:

Unfortunately, the force generated by the electrostatic attraction is very small for common voltages. In fact, it is so small that such meter movement designs are impractical for use in general test instruments. Typically, electrostatic meter movements are used for measuring very high voltages (many thousands of volts). One great advantage of the electrostatic meter movement, however, is the fact that it has extremely high resistance, whereas electromagnetic movements (which depend on the flow of electrons through wire to generate a magnetic field) are much lower in resistance. As we will see in greater detail to come, greater resistance (resulting in less current drawn from the circuit under test) makes for a better voltmeter.

A much more common application of electrostatic voltage measurement is seen in an device known as a Cathode Ray Tube, or CRT. These are special glass tubes, very similar to television viewscreen tubes. In the cathode ray tube, a beam of electrons traveling in a vacuum are deflected from their course by voltage between pairs of metal plates on either side of the beam. Because electrons are negatively charged, they tend to be repelled by the negative plate and attracted to the positive plate. A reversal of voltage polarity across the two plates will result in a deflection of the electron beam in the opposite direction, making this type of meter "movement" polarity-sensitive:

The electrons, having much less mass than metal plates, are moved by this electrostatic force very quickly and readily. Their deflected path can be traced as the electrons impinge on the glass end of the tube where they strike a coating of phosphorus chemical, emitting a glow of light seen outside of the tube. The greater the voltage between the deflection plates, the further the electron beam will be "bent" from its straight path, and the further the glowing spot will be seen from center on the end of the tube.

A photograph of a CRT is shown at the left. In a real CRT, as shown in the above photograph, there are two pairs of deflection plates rather than just one. In order to be able to sweep the electron beam around the whole area of the screen rather than just in a straight line, the beam must be deflected in more than one dimension.

Although these tubes are able to accurately register small voltages, they are bulky and require electrical power to operate (unlike electromagnetic meter movements, which are more compact and actuated by the power of the measured signal current going through them). They are also much more fragile than other types of electrical metering devices. Usually, cathode ray tubes are used in conjunction with precise external circuits to form a larger piece of test equipment known as an oscilloscope, which has the ability to display a graph of voltage over time, a tremendously useful tool for certain types of circuits where voltage and/or current levels are dynamically changing.

Whatever the type of meter or size of meter movement, there will be a rated value of voltage or current necessary to give full-scale indication. In electromagnetic movements, this will be the "full-scale deflection current" necessary to rotate the needle so that it points to the exact end of the indicating scale. In electrostatic movements, the full-scale rating will be expressed as the value of voltage resulting in the maximum deflection of the needle actuated by the plates, or the value of voltage in a cathode-ray tube which deflects the electron beam to the edge of the indicating screen. In digital "movements," it is the amount of voltage resulting in a "full-count" indication on the numerical display: when the digits cannot display a larger quantity.

The task of the meter designer is to take a given meter movement and design the necessary external circuitry for full-scale indication at some specified amount of voltage or current. Most meter movements (electrostatic movements excepted) are quite sensitive, giving full-scale indication at only a small fraction of a volt or an amp. This is impractical for most tasks of voltage and current measurement. What the technician often requires is a meter capable of measuring high voltages and currents.

By making the sensitive meter movement part of a voltage or current divider circuit, the movement's useful measurement range may be extended to measure far greater levels than what could be indicated by the movement alone. Precision resistors are used to create the divider circuits necessary to divide voltage or current appropriately. One of the lessons you will learn in this chapter is how to design these divider circuits.

Review

A "movement" is the display mechanism of a meter.
Electromagnetic movements work on the principle of a magnetic field being generated by electric current through a wire. Examples of electromagnetic meter movements include the D'Arsonval, Weston, and iron-vane designs.
Electrostatic movements work on the principle of physical force generated by an electric field between two plates.
Cathode Ray Tubes (CRT's) use an electrostatic field to bend the path of an electron beam, providing indication of the beam's position by light created when the beam strikes the end of the glass tube.

Creating custom calibration resistances

Creating custom calibration resistances

Resistor, custom value

Often in the course of designing and building electrical meter circuits, it is necessary to have precise resistances to obtain the desired range(s). More often than not, the resistance values required cannot be found in any manufactured resistor unit and therefore must be built by you.

Winding, bifilar Resistor, wire-wound Wire-wound resistor

One solution to this dilemma is to make your own resistor out of a length of special high-resistance wire. Usually, a small "bobbin" is used as a form for the resulting wire coil, and the coil is wound in such a way as to eliminate any electromagnetic effects: the desired wire length is folded in half, and the looped wire wound around the bobbin so that current through the wire winds clockwise around the bobbin for half the wire's length, then counter-clockwise for the other half. This is known as a bifilar winding. Any magnetic fields generated by the current are thus canceled, and external magnetic fields cannot induce any voltage in the resistance wire coil:

As you might imagine, this can be a labor-intensive process, especially if more than one resistor must be built! Another, easier solution to the dilemma of a custom resistance is to connect multiple fixed-value resistors together in series-parallel fashion to obtain the desired value of resistance. This solution, although potentially time-intensive in choosing the best resistor values for making the first resistance, can be duplicated much faster for creating multiple custom resistances of the same value:

A disadvantage of either technique, though, is the fact that both result in a fixed resistance value. In a perfect world where meter movements never lose magnetic strength of their permanent magnets, where temperature and time have no effect on component resistances, and where wire connections maintain zero resistance forever, fixed-value resistors work quite well for establishing the ranges of precision instruments. However, in the real world, it is advantageous to have the ability to calibrate, or adjust, the instrument in the future.

However, most potentiometers provide too large a resistance span over their mechanically-short movement range to allow for precise adjustment. Suppose you desired a resistance of 8.335 kΩ +/- 1 Ω, and wanted to use a 10 kΩ potentiometer (rheostat) to obtain it. A precision of 1 Ω out of a span of 10 kΩ is 1 part in 10,000, or 1/100 of a percent! Even with a 10-turn potentiometer, it will be very difficult to adjust it to any value this finely. Such a feat would be nearly impossible using a standard 3/4 turn potentiometer. So how can we get the resistance value we need and still have room for adjustment?It makes sense, then, to use potentiometers (connected as rheostats, usually) as variable resistances for range resistors. The potentiometer may be mounted inside the instrument case so that only a service technician has access to change its value, and the shaft may be locked in place with thread-fastening compound (ordinary nail polish works well for this!) so that it will not move if subjected to vibration.

The solution to this problem is to use a potentiometer as part of a larger resistance network which will create a limited adjustment range. Observe the following example:

Here, the 1 kΩ potentiometer, connected as a rheostat, provides by itself a 1 kΩ span (a range of 0 Ω to 1 kΩ). Connected in series with an 8 kΩ resistor, this offsets the total resistance by 8,000 Ω, giving an adjustable range of 8 kΩ to 9 kΩ. Now, a precision of +/- 1 Ω represents 1 part in 1000, or 1/10 of a percent of potentiometer shaft motion. This is ten times better, in terms of adjustment sensitivity, than what we had using a 10 kΩ potentiometer.

If we desire to make our adjustment capability even more precise -- so we can set the resistance at 8.335 kΩ with even greater precision -- we may reduce the span of the potentiometer by connecting a fixed-value resistor in parallel with it:

Now, the calibration span of the resistor network is only 500 Ω, from 8 kΩ to 8.5 kΩ. This makes a precision of +/- 1 Ω equal to 1 part in 500, or 0.2 percent. The adjustment is now half as sensitive as it was before the addition of the parallel resistor, facilitating much easier calibration to the target value. The adjustment will not be linear, unfortunately (halfway on the potentiometer's shaft position will not result in 8.25 kΩ total resistance, but rather 8.333 kΩ).


ill, it is an improvement in terms of sensitivity, and it is a practical solution to our problem of building an adjustable resistance for a precision instrument!

Experiment-Basic Concept and Test Equipment-chapter-10

 Experiment-Electromagnetic Induction

PARTS AND MATERIALS

• Electromagnet from previous experiment
• Permanent magnet

See previous experiment for instructions on electromagnet construction.

CROSS-REFERENCE
 "Magnetism and Electromagnetism"

LEARNING OBJECTIVES

• Relationship between magnetic field strength and induced voltage

SCHEMATIC DIAGRAM

ILLUSTRATION

INSTRUCTIONS

Electromagnetic induction Induction, electromagnetic

Electromagnetic induction is the complementary phenomenon to electromagnetism. Instead of producing a magnetic field from electricity, we produce electricity from a magnetic field. There is one important difference, though: whereas electromagnetism produces a steady magnetic field from a steady electric current, electromagnetic induction requires motion between the magnet and the coil to produce a voltage.

Connect the multimeter to the coil, and set it to the most sensitive DC voltage range available. Move the magnet slowly to and from one end of the electromagnet, noting the polarity and magnitude of the induced voltage. Experiment with moving the magnet, and discover for yourself what factor(s) determine the amount of voltage induced. Try the other end of the coil and compare results. Try the other end of the permanent magnet and compare.

If using an analog multimeter, be sure to use long jumper wires and locate the meter far away from the coil, as the magnetic field from the permanent magnet may affect the meter's operation and produce false readings. Digital meters are unaffected by magnetic fields.

Experiment-Basic Concept and Test Equipment-chapter-9

 Experiment-Electromagnetism

PARTS AND MATERIALS

• 6-volt battery
• Magnetic compass
• Small permanent magnet
• Spool of 28-gauge magnet wire
• Large bolt, nail, or steel rod
• Electrical tape

Magnet wire Wire, magnet

Magnet wire is a term for thin-gauge copper wire with enamel insulation instead of rubber or plastic insulation. Its small size and very thin insulation allow for many "turns" to be wound in a compact coil. You will need enough magnet wire to wrap hundreds of turns around the bolt, nail, or other rod-shaped steel form.

Be sure to select a bolt, nail, or rod that is magnetic. Stainless steel, for example, is non-magnetic and will not function for the purpose of an electromagnet coil! The ideal material for this experiment is soft iron, but any commonly available steel will suffice.

CROSS-REFERENCES

 "Magnetism and Electromagnetism"

LEARNING OBJECTIVES

• Application of the left-hand rule
• Electromagnet construction

SCHEMATIC DIAGRAM

ILLUSTRATION

INSTRUCTIONS

Wrap a single layer of electrical tape around the steel bar (or bolt, or mail) to protect the wire from abrasion. Proceed to wrap several hundred turns of wire around the steel bar, making the coil as even as possible. It is okay to overlap wire, and it is okay to wrap in the same style that a fishing reel wraps line around the spool. The only rule you must follow is that all turns must be wrapped around the bar in the same direction (no reversing from clockwise to counter-clockwise!). I find that a drill press works as a great tool for coil winding: clamp the rod in the drill's chuck as if it were a drill bit, then turn the drill motor on at a slow speed and let it do the wrapping! This allows you to feed wire onto the rod in a very steady, even manner.

After you've wrapped several hundred turns of wire around the rod, wrap a layer or two of electrical tape over the wire coil to secure the wire in place. Scrape the enamel insulation off the ends of the coil wires for connection to jumper leads, then connect the coil to a battery.

Electromagnetism

When electric current goes through the coil, it will produce a strong magnetic field: one "pole" at each end of the rod. This phenomenon is known as electromagnetism. The magnetic compass is used to identify the "North" and "South" poles of the electromagnet.

With the electromagnet energized (connected to the battery), place a permanent magnet near one pole and note whether there is an attractive or repulsive force. Reverse the orientation of the permanent magnet and note the difference in force.

Electromagnetism has many applications, including relays, electric motors, solenoids, doorbells, buzzers, computer printer mechanisms, and magnetic media "write" heads (tape recorders, disk drives).

Inductive "kickback"

You might notice a significant spark whenever the battery is disconnected from the electromagnet coil: much greater than the spark produced if the battery is simply short-circuited. This spark is the result of a high-voltage surge created whenever current is suddenly interrupted through the coil. The effect is known as inductive "kickback" and is capable of delivering a small but harmless electric shock! To avoid receiving this shock, do not place your body across the break in the circuit when de-energizing! Use one hand at a time when un-powering the coil and you'll be perfectly safe. This phenomenon will be explored in greater detail in the next chapter 

Three-Phase Transformer Circuits

Since three-phase is used so often for power distribution systems, it makes sense that we would need three-phase transformers to be able to step voltages up or down. This is only partially true, as regular single-phase transformers can be ganged together to transform power between two three-phase systems in a variety of configurations, eliminating the requirement for a special three-phase transformer. However, special three-phase transformers are built for those tasks, and are able to perform with less material requirement, less size, and less weight from their modular counterparts.

Experiment-Basic Concept and Test Equipment-chapter-8

 Experiment-Circuit with a Switch

PARTS AND MATERIALS

• 6-volt battery
• Low-voltage incandescent lamp (Radio Shack catalog # 272-1130 or equivalent)
• Long lengths of wire, 22-gauge or larger
• Household light switch (these are readily available at any hardware store)

Switch

Household light switches are a bargain for students of basic electricity. They are readily available, very inexpensive, and almost impossible to damage with battery power. Do not get "dimmer" switches, just the simple on-off "toggle" variety used for ordinary household wall-mounted light controls.

CROSS-REFERENCES

Lessons In  "Basic Concepts of Electricity"

LEARNING OBJECTIVES

Ammeter design

Ammeter design

Ammeter

A meter designed to measure electrical current is popularly called an "ammeter" because the unit of measurement is "amps."

Taking the same meter movement as the voltmeter example, we can see that it would make a very limited instrument by itself, full-scale deflection occurring at only 1 mA:In ammeter designs, external resistors added to extend the usable range of the movement are connected in parallel with the movement rather than in series as is the case for voltmeters. This is because we want to divide the measured current, not the measured voltage, going to the movement, and because current divider circuits are always formed by parallel resistances.

Experiment-Basic Concept and Test Equipment-chapter-7

 Experiment-Power Dissipation

PARTS AND MATERIALS

• Calculator (or pencil and paper for doing arithmetic)
• 6 volt battery
• Two 1/4 watt resistors: 10 Ω and 330 Ω.
• Small thermometer

The resistor values need not be exact, but within five percent of the figures specified (+/- 0.5 Ω for the 10 Ω resistor; +/- 16.5 Ω for the 330 Ω resistor). Color codes for 5% tolerance 10 Ω and 330 Ω resistors are as follows: Brown, Black, Black, Gold (10, +/- 5%), and Orange, Orange, Brown, Gold (330, +/- 5%).

Do not use any battery size other than 6 volts for this experiment.

The thermometer should be as small as possible, to facilitate rapid detection of heat produced by the resistor. I recommend a medical thermometer, the type used to take body temperature.

CROSS-REFERENCES

Voltmeter design

Voltmeter design

Voltmeter

As was stated earlier, most meter movements are sensitive devices. Some D'Arsonval movements have full-scale deflection current ratings as little as 50 μA, with an (internal) wire resistance of less than 1000 Ω. This makes for a voltmeter with a full-scale rating of only 50 millivolts (50 μA X 1000 Ω)! In order to build voltmeters with practical (higher voltage) scales from such sensitive movements, we need to find some way to reduce the measured quantity of voltage down to a level the movement can handle.

Let's start our example problems with a D'Arsonval meter movement having a full-scale deflection rating of 1 mA and a coil resistance of 500 Ω:

Experiment-Basic Concept and Test Equipment-chapter-6

 Experiment-Nonlinear resistance

PARTS AND MATERIALS

• Calculator (or pencil and paper for doing arithmetic)
• 6-volt battery
• Low-voltage incandescent lamp (Radio Shack catalog # 272-1130 or equivalent)

CROSS-REFERENCES

 "Ohm's Law"

LEARNING OBJECTIVES

• Voltmeter use
• Ammeter use
• Ohmmeter use
• Use of Ohm's Law
• Realization that some resistances are unstable!
• Scientific method

SCHEMATIC DIAGRAM

Experiment-Basic Concept and Test Equipment-chapter-5

 Experiment-Ohm's Law

PARTS AND MATERIALS

• Calculator (or pencil and paper for doing arithmetic)
• 6-volt battery
• Assortment of resistors between 1 KΩ and 100 kΩ in value

I'm purposely restricting the resistance values between 1 kΩ and 100 kΩ for the sake of obtaining accurate voltage and current readings with your meter. With very low resistance values, the internal resistance of the ammeter has a significant impact on measurement accuracy. Very high resistance values can cause problems for voltage measurement, the internal resistance of the voltmeter substantially changing circuit resistance when it is connected in parallel with a high-value resistor.

At the recommended resistance values, there will still be a small amount of measurement error due to the "impact" of the meter, but not enough to cause serious disagreement with calculated values.

Experiment-Basic Concept and Test Equipment-chapter-4

Experiment-Ammeter usage Procedure

PARTS AND MATERIALS

• 6-volt battery
• 6-volt incandescent lamp

Basic circuit construction components such as breadboard, terminal strip, and jumper wires are also assumed to be available from now on, leaving only components and materials unique to the project listed under "Parts and Materials."

CROSS-REFERENCES

 "Basic Concepts of Electricity"

"DC Metering Circuits"

LEARNING OBJECTIVES

• How to measure current with a multimeter
• How to check a multimeter's internal fuse
• Selection of proper meter range

SCHEMATIC DIAGRAM

ILLUSTRATION

INSTRUCTIONS

Current, definition Ampere Amp Unit, ampere

Current is the measure of the rate of electron "flow" in a circuit. It is measured in the unit of the Ampere, simply called "Amp," (A).

The most common way to measure current in a circuit is to break the circuit open and insert an "ammeter" in series(in-line) with the circuit so that all electrons flowing through the circuit also have to go through the meter. Because measuring current in this manner requires the meter be made part of the circuit, it is a more difficult type of measurement to make than either voltage or resistance.

Some digital meters, like the unit shown in the illustration, have a separate jack to insert the red test lead plug when measuring current. Other meters, like most inexpensive analog meters, use the same jacks for measuring voltage, resistance, and current. Consult your owner's manual on the particular model of meter you own for details on measuring current.

When an ammeter is placed in series with a circuit, it ideally drops no voltage as current goes through it. In other words, it acts very much like a piece of wire, with very little resistance from one test probe to the other. Consequently, an ammeter will act as a short circuit if placed in parallel (across the terminals of) a substantial source of voltage. If this is done, a surge in current will result, potentially damaging the meter:

Fuse

Ammeters are generally protected from excessive current by means of a small fuse located inside the meter housing. If the ammeter is accidently connected across a substantial voltage source, the resultant surge in current will "blow" the fuse and render the meter incapable of measuring current until the fuse is replaced. Be very careful to avoid this scenario!

You may test the condition of a multimeter's fuse by switching it to the resistance mode and measuring continuity through the test leads (and through the fuse). On a meter where the same test lead jacks are used for both resistance and current measurement, simply leave the test lead plugs where they are and touch the two probes together. On a meter where different jacks are used, this is how you insert the test lead plugs to check the fuse:

Build the one-battery, one-lamp circuit using jumper wires to connect the battery to the lamp, and verify that the lamp lights up before connecting the meter in series with it. Then, break the circuit open at any point and connect the meter's test probes to the two points of the break to measure current. As usual, if your meter is manually-ranged, begin by selecting the highest range for current, then move the selector switch to lower range positions until the strongest indication is obtained on the meter display without over-ranging it. If the meter indication is "backwards," (left motion on analog needle, or negative reading on a digital display), then reverse the test probe connections and try again. When the ammeter indicates a normal reading (not "backwards"), electrons are entering the black test lead and exiting the red. This is how you determine direction of current using a meter.

Metric prefix

For a 6-volt battery and a small lamp, the circuit current will be in the range of thousandths of an amp, or milliamps. Digital meters often show a small letter "m" in the right-hand side of the display to indicate this metric prefix.

Try breaking the circuit at some other point and inserting the meter there instead. What do you notice about the amount of current measured? Why do you think this is?

Re-construct the circuit on a breadboard like this:

Students often get confused when connecting an ammeter to a breadboard circuit. How can the meter be connected so as to intercept all the circuit's current and not create a short circuit? One easy method that guarantees success is this:

• Identify what wire or component terminal you wish to measure current through.
• Pull that wire or terminal out of the breadboard hole. Leave it hanging in mid-air.
• Insert a spare piece of wire into the hole you just pulled the other wire or terminal out of. Leave the other end of this wire hanging in mid-air.
• Connect the ammeter between the two unconnected wire ends (the two that were hanging in mid-air). You are now assured of measuring current through the wire or terminal initially identified.

Again, measure current through different wires in this circuit, following the same connection procedure outlined above. What do you notice about these current measurements? The results in the breadboard circuit should be the same as the results in the free-form (no breadboard) circuit.

Building the same circuit on a terminal strip should also yield similar results:

The current figure of 24.70 milliamps (24.70 mA) shown in the illustrations is an arbitrary quantity, reasonable for a small incandescent lamp. If the current for your circuit is a different value, that is okay, so long as the lamp is functioning when the meter is connected. If the lamp refuses to light when the meter is connected to the circuit, and the meter registers a much greater reading, you probably have a short-circuit condition through the meter. If your lamp refuses to light when the meter is connected in the circuit, and the meter registers zero current, you've probably blown the fuse inside the meter. Check the condition of your meter's fuse as described previously in this section and replace the fuse if necessary.

Experiment-Basic Concept and Test Equipment-chapter-3

Experiment-A Very Simple Circuit

PARTS AND MATERIALS

• 6-volt battery
• 6-volt incandescent lamp
• Jumper wires
• Breadboard
• Terminal strip

From this experiment on, a multimeter is assumed to be necessary and will not be included in the required list of parts and materials. In all subsequent illustrations, a digital multimeter will be shown instead of an analog meter unless there is some particular reason to use an analog meter. You are encouraged to use both types of meters to gain familiarity with the operation of each in these experiments.

CROSS-REFERENCES

Lessons In Electric Circuits, Volume 1, chapter 1: "Basic Concepts of Electricity"

LEARNING OBJECTIVES

Experiment-Basic Concept and Test Equipment-chapter-2

 Experiment-Ohmmeter(Insulation tester)Usage

PARTS AND MATERIALS

• Multimeter, digital or analog
• Assorted resistors (Radio Shack catalog # 271-312 is a 500-piece assortment)
• Rectifying diode (1N4001 or equivalent; Radio Shack catalog # 276-1101)
• Cadmium Sulphide photocell (Radio Shack catalog # 276-1657)
• Breadboard (Radio Shack catalog # 276-174 or equivalent)
• Jumper wires
• Paper
• Pencil
• Glass of water
• Table salt

Experiment-Basic Concept and Test Equipment-chapter-1

Voltmeter usage Procedure 

PARTS AND MATERIALS

• Multimeter, digital or analog
• Assorted batteries
• One light-emitting diode (Radio Shack catalog # 276-026 or equivalent)
• Small "hobby" motor, permanent-magnet type (Radio Shack catalog # 273-223 or equivalent)
• Two jumper wires with "alligator clip" ends (Radio Shack catalog # 278-1156, 278-1157, or equivalent)

A multimeter is an electrical instrument capable of measuring voltage, current, and resistance. Digital multimeters have numerical displays, like digital clocks, for indicating the quantity of voltage, current, or resistance. Analogmultimeters indicate these quantities by means of a moving pointer over a printed scale.

Experiments-Introduction-Chapter-2

Setting up a Home Lab

In order to build the circuits described in this volume, you will need a small work area, as well as a few tools and critical supplies. This section describes the setup of a home electronics laboratory.

Work area

A work area should consist of a large workbench, desk, or table (preferably wooden) for performing circuit assembly, with household electrical power (120 volts AC) readily accessible to power soldering equipment, power supplies, and any test equipment. Inexpensive desks intended for computer use function very well for this purpose. Avoid a metal-surface desk, as the electrical conductivity of a metal surface creates both a shock hazard and the very distinct possibility of unintentional "short circuits" developing from circuit components touching the metal tabletop. Vinyl and plastic bench surfaces are to be avoided for their ability to generate and store large static-electric charges, which may damage sensitive electronic components. Also, these materials melt easily when exposed to hot soldering irons and molten solder droplets.

EIA-Experiments-Introduction-Chapter-1

    Introduction-Chapter-1 

    Electronics as Science

    Dear Readers 

Glad to inform you that we have going to provide experiments procedure  of equipment/instruments /self made device with help of your own home mad lab. The LAB experiment based on EIA (Electrical Instrumentation and Automation).

List of content which will explain in experiment topic as follows

INTRODUCTION
BASIC CONCEPT OF TEST EQUIPMENT
AC CIRCUIT
DC CIRCUITS
DISCRETE SEMICONDUCTOR CIRCUITSANALOG INTEGRATED CIRCUITSDIGITAL INTEGRATED CIRCUIT
555 TIMER CIRCUIT

Concept of Magnetic Flux and Magnetic Lines of Force

Flux and Magnetic Lines of Force

Concept of electric flux was used in connection with the electric field in whichwhic electric flux density at a point in free space is directly proportional to the electric field intensity at that point. Analogous relations exist for the magnetic field in that the magnetic flux density at a point in free space is directly proportional to the magnetic field intensity at that point, as expressed by

.      [3-15]

where B = magnetic flux density and μ0 = magnetic permeability of free space. In the rationalized MKS μ0 has the value of 4π x 10-7 henry per meter and B is expressed in webers per square meter.
The magnetic field is a field of force and requires energy for its production. A magnet when brought into the magnetic field produced by another magnet or by a current in a circuit experiences a force. Although a positive or negative charge can be isolated, a magnetic pole cannot exist by itself since every magnet has an equal number of poles of opposite polarity. The simplest magnet has one north pole and one south pole. However, if a north pole could exist by itself without the accompanying south pole, and this north pole were brought to within a distance of r1 of the filament in Fig. 3-2, it would experience a force in a direction tangent to the circle of radius r1 as determined by the right-hand rule. The locus of constant force would be a cylinder of radius r1 concentric with the filament. The magnetic field can therefore be represented by lines of force.

The Unit Magnet Pole

Magnet Pole

It is shown that electric charges produce an electric field and that forces between electric charges exist. The force between point charges isolated in free space which expresses Coulomb's law for point electrical charges. A similar law known as Coulomb's law of force between point magnetic poles applies to magnetic fields in free space and is given by the following formula

[3-19]

CONDUCTOR AND INSULATOR TABLES

Gage size, wire Wire size, gage scale
Soild copper wire table:

Size        Diameter         Cross-sectional area       Weight
AWG          inches        cir. mils     sq. inches   lb/1000 ft
================================================================
4/0 -------- 0.4600 ------- 211,600 ------ 0.1662 ------ 640.5
3/0 -------- 0.4096 ------- 167,800 ------ 0.1318 ------ 507.9
2/0 -------- 0.3648 ------- 133,100 ------ 0.1045 ------ 402.8