LAB MANUAL/EMIT

EXPERIMENT NO.1PART A

TITLE: Digital Multimeter.

AIM: Perform following using analog and digital multi-meter 1. Measurement of dc voltage, dc current, ac (rms) voltage, ac (rms) current, resistance and

capacitance. 2. Understand the effect of decimal point on resolution. 3. Comment on bandwidth. (Only for Digital Multi-meter) 4. To test continuity, PN junction and transistor. Calculate mean, standard deviation,

average deviation, and variance of measured qty.5. Calculate mean, standard deviation, average deviation, and variance of measured qty.

APPARATUS:

Sr. No. Instrument Model

1 DMM

2 Function Generator

3 DC Power Supply

4 Diode , Transistor Ge/Si Diode, PNP/NPN Transistor

THEORY:

Multi-meters: A multimeter or a multitester, also known as a volt/ohm meter or VOM, is an electronic measuring instrument that combines several functions in one unit. A standard multimeter may include features such as the ability to measure voltage, current and resistance.

A multimeter can be a hand-held device useful for basic fault finding and field service work or a bench instrument which can measure to a very high degree of accuracy. They can be used to troubleshoot electrical problems in a wide array of industrial and household devices such as batteries, motor controls, appliances, power supplies, and wiring systems.

Quantities measured: Contemporary multimeter can measure many quantities.

The common ones are:

Voltage in volts, Current in amperes, Resistance in ohms.

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Additionally, multimeter may also measure:

1. Capacitance in farads. Frequency in hertz, Duty cycle as a percentage.

2. Temperature in degrees Celsius or Fahrenheit.

3. Conductance in siemens. Inductance in henrys

4. Audio signal levels in decibels.

Digital Multimeter may also include circuits for:

1. Continuity that beeps when a circuit conducts.

2. Diodes and Transistors.

Various sensors can be attached to multimeter to take measurements such as:

1. light level

2. Acidity/Alkalinity(pH)

3. Wind speed

4. Relative humidity

The first digital multimeter was manufactured in 1955 by Non Linear Systems.

There are two categories of multimeter

1. Analog Multimeter

2. Digital Multimeter (often abbreviated DMM.)

1. Analog Multimeter:

Fig.no.1 : Analog Multimeter

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Analog meters are older and still preferred by many engineers. One reason for this is that analog meters are more sensitive to changes in the circuit that is being measured.

Analog multimeters are continuously read the test value. If there are slight changes in readings, the needle of an analog multimeter will track them. This continuous tracking feature becomes important when testing capacitors or coils.

Typically an analog meter will have a panel adjustment to set the zero-ohms calibration of the meter, to compensate for the varying voltage of the meter battery.

2. Digital Multimeter:Multimeters are designed and mass produced for electronics engineers. Digital meters give an output in numbers, usually on a liquid crystal display.

Digit Meter Displays:

Fig No 2: Digital Multimeter

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1) Digital multimeter FundamentalsDigital Multimeter Display:1. Digital Display- 3 ½ digit, 7 segment.Liquid crystal display with automatic decimal point

positioning, updated two times per second. When the meter is first turned on, all display

segments appear while the instrument performs a brief power-up self-test.

1. 3 1/2 digit displays:

It can be used to show values from 0999 to 1999, and can include a decimal point, by lighting up the red segments, to suit the number you want.

2. 3 ¾ digit display:

The front digit of the meter can take on values from 0 through 3, thereby doubling the count (resolution) from say 0.999 to 3.999 .

BLOCK DIAGRAM OF DMM:

Working of DMM:The block diagram of DMM is as shown in figure.

1. Resistance measurement –An unknown resistor is connected across its input probes. Rotary

switch is in position–1. Some current flows through the resistor, from constant current source.

Now according to Ohm’s law voltage is produced across it. This voltage is directly proportional

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to its resistance. This voltage is buffered by the buffer amplifier and then fed to A/D converter,

to get digital display in Ohms.

2) AC voltage Measurement– An unknown AC voltage is connected across input probes.

Rotary switch is in position–2. The voltage is attenuated, if it is above the selected range and

then rectified to convert it into proportional DC voltage. It is then fed to A/D converter to get the

digital display in Volts.

3) AC current Measurement – this circuit measures the current indirectly. Because the circuit

can measure only voltage and the A/D converter can convert voltage into proportional digital

signals. So the current is converted into proportional voltage first and then measured.

An unknown AC current is connected across input probes. The switch is in position–3. The

current is converted proportionally into voltage with the help of I–V converter and then rectified.

Now the voltage in terms of AC current is fed to A/D converter to get digital display in Amperes.

4) DC current Measurement -An unknown DC current is connected across input probes. The

switch is in position–4. The current is converted proportionally into voltage with the help of I–V

converter. Now the voltage in terms of DC current is fed to A/D converter to get the digital

display in Amperes.

5) DC voltage Measurement An unknown DC voltage is connected across input probes. The

switch is in position–5. The voltage is attenuated, if it is above the selected range and then

directly fed to A/D converter to get the digital display in Volts.

2) Front Panel Description of DMM1. Function Selector Rotary Switch-Turn to select any of 10 different functions, or OFF.

2. Volt, Ohms, Diode Test Input Terminal-Input terminal used in conjunction with the volts,

mV (ac or dc), ohms, or diode test position of the function selector rotary switch.

3. COM Common Terminal-Common or return terminal used for all measurements.

4. Milliamp/Micro amp Input Terminal-Input terminal used for current measurements up to

320 mA (ac or dc) with the function selector rotary switch in the mA or μA positions.

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5. Amperes Input Terminal-Input terminal used for current measurements up to 10A continuous.

6. Back Light- When this button is pushed, the back light of display is ON, after about 5Sec it is

self-OFF.

3) Measurement of parameters

3.1 Steps for measuring ac voltage with a digital multimeter:

1. Turn the dial to ṽ. Some digital multimeters (DMMs) also include mV . If voltage in the circuit is unknown, set the range to the highest voltage setting and set the dial on ṽ.

2. First insert the black lead into the COM jack.

3. Next insert the red lead into the VΩ jack. When finished, remove the leads in reverse order: red first, then black.

4. Connect the test leads to the circuit: black lead first, red second.

5. Read the measurement in the display. When finished, remove the red lead first, black second.

3.2 Measure Frequency:

If your digital multimeter offers a frequency setting (Hz is the symbol) on the dial:

1. Turn the dial to Hz. It usually shares a spot on the dial with at least one other function. Some meters enter the frequency through a secondary function accessed by pushing a button and setting the rotary switch to ac or dc.

2. First insert the black test lead into the COM jack.

3. Then insert the red lead into the V Ω jack. When finished, remove the leads in reverse order: red first, then black.

4. Read the measurement in the display. The abbreviation Hz should appear to the right of the reading.

3.3 Measure Capacitance :

A multimeter determines capacitance by charging a capacitor with a known current, measuring the resulting voltage, then calculating the capacitance.

Warning: A good capacitor stores an electrical charge and may remain energized after power is removed. Before touching it or taking a measurement, a) turn all power OFF, b) use your multimeter to confirm that power is OFF and c) carefully discharge the capacitor by connecting a resistor across the leads

3.4. Test continuity:

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1. Turn the dial to Continuity Test mode (  ). It will likely share a spot on the dial with one or more functions, usually resistance (Ω). With the test probes separated, the multimeters display may show OL and Ω.

3.5. Test Diode:

Digital multimeters can test diodes using one of two methods:

Diode Test mode: almost always the best approach. Or Resistance Test Method

Procedure using Diode Test Method:

1. Make certain a) all power to the circuit is OFF and b) no voltage exists at the diode. Voltage may be present in the circuit due to charged capacitors. If so, the capacitors need to be discharged. Set the multimeter to measure ac or dc voltage as required.

2. Turn the dial (rotary switch) to Diode Test mode ( ). It may share a space on the dial with another function.

3. Connect the test leads to the diode. Record the measurement displayed.

4. Reverse the test leads. Record the measurement displayed.

Things to know about the Resistance mode when testing diodes:

Should not be taken when a diode is connected in a circuit, since it can produce a false reading. CAN be used to verify a diode is bad in a specific application after a Diode Test indicates a diode

is bad.

A diode is best tested by measuring the voltage drop across the diode when it is forward-biased. A forward-biased diode acts as a closed switch, permitting current to flow.

3.6. Measure resistance:

How to measure resistance

1. Turn power to circuit OFF. If a circuit includes a capacitor, discharge the capacitor before taking any resistance reading. Do not touch resistance under measurement.

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2. Turn dial to Ω (resistance, or ohms), which often shares a spot on the dial with one or more other test/measurement modes (continuity, capacitance or diode; see illustration below).

3.7. Measure DC voltage:

1. Turn dial to . Some digital multimeters (DMMs) also include . If uncertain of

which to choose, start with , which handles higher voltage.

3.8. Test transistor:

Transistors register as two diodes connected back-to-back when tested with a multimeters “resistance “or “� diode check”. Meter will display the actual forward voltage of the PN junction and not just whether or not it conducts current.

PNP transistor meter check: (a) forward B-E, B-C, resistance is low; (b) reverse B-E, B-C, resistance is ∞.Checking NPN transistor (diode check):

1. First, you should read the pertinent transistor's datasheet to identify the pin-out (i.e., which pins

are the B (base), C (collector) or E (emitter). Set Diode Check mode.

2. Touch the DMM's + probe (red, if you have the probe wires plugged in to the meter correctly) to

the transistor's B pin, and then touch the - probe (black) to the transistor's C pin. You should read

between around 0.6V to 0.7V on your meter display. This checks the forward voltage of the B-C

junction "diode".

3. Keeping the red probe on the B pin, now touch the black probe on the E pin. You should also read

around 0.6V to 0.7V. This checks the forward voltage of the B-E junction "diode".

4. Now touch the black probe on the B pin, and the red probe on the C pin. Your meter should read

"over-range".

5. Keeping the black probe on the B pin, now touch the red probe on the E pin. You should also read

"over-range". This checks the reverse voltage of the B-E junction diode.

6. Lastly, put the red probe on the C pin, and the black probe on the E pin, note the reading. Then

reverse the two probes and check the reading again. Both of these should show "over-range".

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3.9 Safety tips:

Choose the right tool

1. Always select a multimeter suitable for the measurement location.

2. Make certain the meter has the proper Overvoltage Installation Category rating (CAT II, CAT III or CAT IV) for the application. Always choose a tool rated for the highest category in which it could potentially be used. CAT ratings are discussed in more detail below.

3. Example: To measure 480 V in an electrical distribution feeder panel, use a meter rated at CAT III-600 V, CAT-III-1000 V or CAT IV-600 V.

SPECIFICATIONS:1. Resolution

The resolution of a multimeter is often specified in "digits" of resolution. For example,

the term 5½ digits refer to the number of digits displayed on the readout of a multimeter.

A 5½ digit multimeter would have five full digits that display values from 0 to 9 and one half

digit that could only display 0 or 1. Such a meter could show positive or negative values from 0

to 199,999. A 3¾ digit meter can display a quantity from 0 to 3,999.

2. Accuracy

Accuracy is specified for a period of 1 year after calibration and at 18-280C with relative

humidity to 80%. Normally the error is quoted in the form:

± (percent of reading + number of digits)

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Let a digital multimeter is set to a 19.99 range. In this case one digit or one count will be equal to

0.01. When measuring a voltage of 10 volts on the 19.99 volt range, the uncertainty is quoted as

(0.002 % + 2 counts) then the total uncertainty for this reading can be calculated as:

± (0.002 % x 10 V + 2 x 0.01V)

= ± (0.02 V + 0.02V)

= ± 0.04 V

3. Environmental and other external specifications

A digital multimeter will only be able to meet its specifications when it is within a certain

environment. Conditions such as temperature, humidity and the like will have impact on the

performance.

CIRCUIT DIAGRAM

Circuit Diagram for AC current measurement:

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DMM

Function Generator

+

_

Rheostat

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OBSERVATION TABLE

1) AC voltage measurement of mains supply

2) AC Current Measurement:

Sr. No. Voltage

(VPk-Pk)

Resister

(R)

Current measured on DMM (Ipr.)

Voltage

(Vrms)

Current Calculated(ITh. =V/R)

1

2

3

CIRCUIT DIAGRAM

3) DC current measurement:

OBSERVATION TABLE

Sr. No. Voltage

(V)

Resister

(R)Current measured on

DMM (Ipr.)

Current Calculated(ITh. =V/R)

1

2

3

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DMMDC Power Supply

Rheostat

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4) DC VOLATGE MEASUREMENT

Sr. No.Voltage on power supply

(V)Voltage on DMM

1

2

3

5) RESISTANCE MEASUREMENT

Sr. No.Resistance value using colour

codeResistance value on DMM

1

2

3

6) DIODE TESTING

Forward bias Voltage Reverse Bias Voltage Comment

Diode OK / Faulty

Diode OK / Faulty

7. Duty Cycle and Freq:

Voltage Duty Cycle on

CRO

Duty Cycle on

DMM

Accuracy

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8. Transistor test:

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CONCLUSIO

N:________________________________________________________________________

__________________________________________________________________________

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PART B

TITLE: Statistical Analysis

AIM: Carry out Statistical Analysis of Digital Voltmeter

Calculate mean, standard deviation, average deviation, and variance.

THEORY:Arithmetic Mean:

When number of readings for the same quantity is taken, then the most likely value from the set of measured values is called as arithmetic mean.

Mathematically it is given by

If x1, x2, x3……xn are the observations then

ARITHMETIC MEAN, (m) = (x1+x2+x3+……..+xn)/n

where n is the sample size and the x correspond to the observed valued.

Deviation From Arithmetic Mean:

It indicates departure of the reading from the arithmetic mean of the group of readings taken for the same quantity being measured.

Mathematically it is given by

DEVIATION FROM ARITHMETIC MEAN, (d) = xi – m

Average Deviation:

It is defined as the sum of the absolute values of deviations divided by the total number of readings. Mathematically it is given by

AVERAGE DEVIATION = (|d1| + |d2| + |d3| +……..+ |dn|)/n

Standard Deviation:

It is defined as the square root of the sum of the individual deviations squared, divided by the total number of readings.

Mathematically it is given by

S.D = ((d12 + d2

2 + d32 +………. + dn

2)/ n-1 )1/2

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Variance :

The variation on either side of the center or deviation is another important characteristic of our measurements. If we take the sample mean as the center of our data, then the sample deviation is the difference between the measured value and the sample mean:

VARIANCE, (V) = (S.D)2

Problem statement

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Conclusio

n:___________________________________________________________________________________

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