Measuring instruments

Measuring Instruments

Prepared by:Dharmendra Sadhwani

Assistant ProfessorEC department SISTec-E

SISTEC-E

Constructing a Series Circuit◦ Ohm’s Law Review◦ Breadboard Overview◦ DC Power Supply Review

Measuring the D.C. Voltage in the Series Circuit◦ Multimeter Overview

2

Objectives

SISTEC-E

Determine the current

Use Ohm’s Law: V = I x R

3V = I x 1000 Ω

Solve for I: I=3V / 1000 Ω =

3milliAmps

Today we will build this series circuit

3V

0V

R = 1K Ω

I = ? Amps

SISTEC-E

1)A 1K Ohm Resistor2)Breadboard3)DC Voltage Source4)2 sets of Banana Clip

to mini-grabber wires

How to Build the Circuit

We need 4 components

3V

0V

R = 1K Ω

I = 3mA

SISTEC-E

The Breadboard

The breadboard is used to build circuits without the need of soldering

You can plug resistors and wires right into the board

SISTEC-E

The Breadboard

The left and right side columns are connected horizontally shorted

BR

IDG

E

The columns between the blue and red bars crossing the bridge are vertically shorted

The

SISTEC-E

The The left and right side columns are

connected horizontally shorted

The columns between the blue and red bars crossing the bridge are vertically shorted

The Breadboard

SISTEC-E

Setting up the breadboard

Plug 1 end of the 1K resistor in the top row, on the left side of the bridge

Plug the other end of the 1K resistor in the top row, on the right side of the bridgetor into the top row, on the right side of the bridge

of the resistor into the top row, on the right side of the bridge

SISTEC-E

This DC Power supply is capable of generating voltages from -25V to 25V.

For this lab, we will be using the 6V supply terminals.

First, press the Power Button to turn it on.

Setting Up the DC Power Supply

SISTEC-E

Press Output On/Off once to turn on the output.

Press the +6V button to tell the power supply that we want to alter the output from the 6V terminals.

Once done, your screen should look the same as it does on this slide.


SISTEC-E

Use the dial to increase the display value to 3 volts as shown.

Note: You can safely ignore the value of the right most digit for this experiment.

Once you have reached 3V, Press Output On/Off once to turn the output OFF while you hook up the circuit.


This is the digit we want to adjust

Press this arrow toSelect the

desired digit

Rotate this dial toalter the output value.

SISTEC-E

Plug the ‘banana’ end of your cables into the 6V terminals of your power supply

Connect the mini-grabber ends of the cables around your 1K resistor on the breadboard

After attaching the mini-grabbers to your circuit, press the Output On/Off to apply 3 Volts across your 1K resistor

Connecting the Power Supply to your Circuit

SISTEC-E

Measuring the Voltage Across the Resistor…Using the Multimeter

SISTEC-E

What is a Multimeter?

A tool capable of measuring a variety of different quantities.

Possible Measurements◦ Current (Amperes)◦ Resistance (Ohms)◦ Voltage (Volts)

14

SISTEC-E

www.sistec.ac.in

How is the Multimeter different than the Oscilloscope?

Numerical Output Displayed

Represents a complete signal with a single value.

Measures voltage, current and resistance.

Graphical Output Displayed

Shows how a signal changes over time

Many only display voltage

15

Multimeter Oscilloscope

SISTEC-E

www.sistec.ac.in

Explanation of ControlsSetting up the multimeter for various measurements.

SISTEC-E

Taking measurements with the Multimeter

First, we connect our wires.

One wire is always connected to the black terminal. This is called the common terminal.

The red terminal is used when measuring voltage, resistance and small currents.

The white terminal is used when measuring large currents.

SISTEC-E


Next, we turn it on and select the item to measure. Choose from:

◦ Current◦ Resistance◦ Voltage

18

Power Button

SISTEC-E

www.sistec.ac.in


Now, we select our scale. Either select a scale appropriate for your measurement or

choose AUTO and let the multimeter select the appropriate scale for you.

Measuring the voltage from across the 1K resistor (~3V), you wouldn’t want to choose 200mV (much too small) or 200V (much too large). Instead, the 2V selection is more suitable.

19

SISTEC-E

www.sistec.ac.in


20

While your circuit is attached to the power supply…

Attach the minigrabber end around the 1K resistor

Press the “POWER” button on the multimeter and take a reading!!

SISTEC-E

www.sistec.ac.in

Building & Verifying Series Circuit #2

21

3V R2 = 1KΩ

0V

R1 = 1KΩ

Ohm’s Law States:

V(R1) = 1.5mA x 1K Ω = 1.5V

V(R2) = 1.5mA x 1K Ω = 1.5V

We are now going to build the circuit, and verify the voltage drops…

SISTEC-E

Resistors connected by only 1 terminal, back-to-back, are considered to be in ‘seriesOhm’s Law States:

V(R1) = 1.5mA x 1K Ω = 1.5V

V(R2) = 1.5mA x 1K Ω = 1.5VWe are now going to

build the circuit, and verify the voltage drops…

www.sistec.ac.in

Setting up the breadboard

22

Turn off the 3V supply and disconnect the cables

Disconnect the cables to the minigrabbers to the multimeter

Obtain a 2nd 1K resistor

Plug one end of the resistor into a hole in the same row as the end of the other resistor

Plug the other end into a hole in another row

SISTEC-E

Turn off the 3V supply and disconnect the cables

Disconnect the cables to the minigrabbers to the multimeter

Obtain a 2nd 1K resistor

Plug one end of the resistor into a hole in the same row as the end of the other resistor

Plug the other end into a hole in another row www.sistec.ac.in


23

Set the Power Supply to 3V

Attach the power supply leads as follows

Measure the voltage across each resistor with the multimeter

SISTEC-E

www.sistec.ac.in

Resistors in Parallel

24

Resistors connected at 2 terminals, sharing the same node on each side, are considered to be in ‘parallel’

3V

0V

R1 = 1K Ω

The voltage is the same on both branches of the circuit

The current will split!

It is now up to you to build this circuit and verify the voltages

R2 = 1K Ω

SISTEC-E

www.sistec.ac.in

Including a Diode In the Circuit

25

We’ll use LEDs (Light Emitting Diodes) for our circuits.

3V R1

= 1

KΩ

0V

Unlike resisters, the two diode leads (wires) must be connected in the correct way.

The longer lead (anode) should be connect so that current flows through it and to the shorter lead (cathode).

Note: In some diodes, a stripe is used to indicate the cathode lead. Round diodes often have a flat side, indicating the cathode.

SISTEC-E

www.sistec.ac.in

Your Turn1) Build the parallel circuit (in the last slide) and measure

the voltage across it◦ Using Ohm’s Law, what is the current through each

resistor?◦ What is the total current in the circuit?

2) In your parallel circuit, change one of the 1K resistors to a 2K resistor◦ Measure the voltage across each resistor◦ Use Ohm’s law to determine the current through each

resistor3) Rebuild the two resistor series circuit…

◦ Change one of the 1K resistors to a 2K resistor◦ Measure the voltage across each resistor◦ Use Ohm’s law to determine the current through each

resistor

26

SISTEC-E

www.sistec.ac.in

Your Turn4) Build a circuit with a diode in series with a 1K resistor

◦ Using Ohm’s Law, what is the current through the resistor?◦ What is the total current in the circuit?◦ Reverse the anode and cathode connections of the diode

and observe the results.

5) Build a circuit with a diode in series with 2 parallel 1K resistors

◦ Measure the voltage across each resistor◦ Use Ohm’s law to determine the current through each

resistor

6) Don’t forget the HW!

27

SISTEC-E

www.sistec.ac.in

Digital Multimeter

SISTEC-E

What is a Digital Multimeter?A digital Multimeter measures AC / DC

voltage, resistance, and current in an electric circuit. It is highly accurate and displays an LCD number readout.

SISTEC-E

Test leads are used to connect the multimeter to the circuit to be tested.

Test Leads

SISTEC-E

Function/Range Switch

DC Voltage

Battery Test

DC Current

AC Voltage

Resistance

Continuity Test

SISTEC-E

Voltage Meter The voltmeter is used

to measure the voltage potential across a component in an active circuit.

It can be used to measure either DC or AC voltages.

AC voltage can ONLY measure sinusoidal (SINE) waveforms.

SISTEC-E

Test Lead Connections - Voltage

Plug the RED test lead into the jack labeled V/ and the test lead into the jack labeled COM (common).

SISTEC-E

The ohmmeter is used to measure the resistance of a component.

POWER CANNOT be applied to the component being tested.

The ohmmeter actually applies a small voltage and uses Ohm’s law to calculate the resistance from the measured current.

Ohmmeter

SISTEC-E

Test Lead Connections - Resistance

Same as voltage measurement

SISTEC-E

AmmeterThe ammeter is used to measure the current through a component in an active circuit.

It can be used to measure only DC current.

Some multimeters can also measure AC current.

SISTEC-E

Test Lead Connections - Current

Plug the RED test lead into the jack labeled mA for milliamps or into the jack labeled 10A for circuits with high current levels. Plug the BLACK test lead into the jack labeled COM.

Be certain to select the range according to the test lead connections.

Observe proper polarity.

SISTEC-E

Be sure the test leads are connected appropriately for the intended measurement.

Turn the meter’s Function/Range switch to the function (ACV, DCV, DCA or ) to be measured.

Select a range which is higher than the expected value.

Connect the test leads to the circuit/component being tested. Observe proper polarity.

Turn the meter’s Function/Range switch to reduce the range and increase the accuracy.

Record results. Remember to turn the power OFF when finished.

Basic Instructions

SISTEC-E

Special FunctionsContinuity Tester

Used to test the continuity between two points. Will produce an audio tone.

Diode Tester

Used to test the resistance in a diode for forward bias and reverse bias.

Battery Tester

Used to test 9 volt and 1.5 volt (AAA,AA, C, D) batteries.

SISTEC-E

Check meter’s battery Review instructions to make sure all the

meter’s settings are accurate for the type of testing being conducted

Check to see if test leads are broken or not connected properly

Inspect and test the fuse

If the Meter Malfunctions :

SISTEC-E

Function Generator

SISTEC-E

Introduction

A function generator is used in many engineering fields to generate a wide variety of synthesized electrical signals such as the sine, square, triangle and ramp functions. These signals are used for testing and diagnostic applications.

SISTEC-E

SISTEC-E

www.sistec.ac.in 44

THANK YOU

Measuring instruments

Business

Transcript of Measuring instruments