Multimeter & Oscilloscopes

Multimeter & Oscilloscope

Safety Statement

Information and Administration: The course will start at 9.00am and finish at 5:00pm. Lunch and refreshments will be provided at the times advised by the training instructor. Workshop Safety • It will be expected that all necessary workshop health and safety procedures are followed e.g. the wearing of suitable work wear, safety footwear, eye and ear protection when in the practical workshops is mandatory. We recommend that barrier cream and workshop gloves are used at all times. • Ensure that you are fully aware of the emergency stop procedure for any of the rotating equipment used during the course. While working on rotary test equipment or engines, please ensure that all loose clothing is secure and can not get caught in the equipment or engine parts.

Objectives

On completion of the course, technicians will be able to:

• Choose and correctly use the measurement apparatus and interpret the various signals.

• Safely measure the various sensors and actuators fitted to the vehicle.

• Make use of guided diagnostic tests.

• Make an effective diagnosis with the help of these measurement apparatus.

Introduction

Fire Escape Smoking Areas Toilets Mobile Phone, please switch off or on silent

Group introductions…..

Content

• Testing active circuits

Different types of multimeters

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• Testing inactive circuits

Multimeter measurements

•

• Electrical load detection/location

The oscilloscope

•

• Testing starting/charging circuits

Leads & clamps

•

• Testing preheating circuits

Basic concepts

•

• Checks on sensors & actuators

Main scope settings

•

• Diagnosing multiplexing networks

Oscilloscope options menu

•

• Permanent and intermittent fault finding

Use of several scope channels

•

Introduction to Multimeters

• One of the most important electrical measurement tools in the current automotive repair workshop is the multimeter.

• A Multimeter is an electronic measuring instrument

• The Multimeter is used to measure various electrical parameters.

• Voltage, resistance, current measurement is incorporated into all types of multimeter, although, depending on models and brands, more measurements may be available.

• For automotive work intelligent multimeters are used, which include a greater number of functions such as RPM, frequencies, duty cycle, pulse times, dwell, temperature tests, diode testing, etc.

• There are 2 types of Multimeters – ANALOGUE or DIGITAL (more common)

Common Multimeter Symbols

These symbols are often found on a multimeter and schematics.

They are designed to symbolize components and reference values

Analogue Multimeter

Analogue Multimeters (AMM) use the force from the circuit to move a needle pointer over a calibrated scale to indicate the measurements, they were the first used to indicate voltage, resistance and in some cases even current levels.

Analogue Multimeters are not as common in the modern era. They can still be preferable in some cases, for example when checking a rapidly varying value but the downside of the AMM is the accuracy due to numerous reasons.

Analogue Multimeter Parts

• Range Selector

• Reading Scale

• Needle Pointer

• Terminal Meter

• Pointer Zero Adjustment

• Ohm Pointer Zero Adjustment,

To set this;

• Set range to lowest Ohm reading • Touch two probes together • Adjust the needle pointer to zero

Analogue Multimeter Features

AMM use the power from the circuit to operate the needle pointer. They must have high Sensitivity (impedance) of at least 20kΩ/V or they may upset the circuit while testing and give an incorrect reading. Batteries inside the AMM provide a small current to the circuit for the resistance measurements.

Digital Multimeter

A Digital Multimeter (DMM) is made up of an electronic testing circuit and a liquid crystal display screen (LCD).

In spite of its lower data display speed, it can incorporate safety systems to protect the device against reverses of polarity or measurements on unsuitable scales. A digital multimeter with the highest possible impedance should be used so it affects the electrical circuit under test as little as possible and does not damage it. Some Digital Multimeters have an “Auto-Range” function, these type of DMM will automatically set the range to suit the circuit being tested.

Digital Multimeter Parts

Digital Multimeter Features

One of the key things of any DMM is the types of measurement and ranges that can be made. Batteries inside the DMM provide a small current to the circuit for the resistance measurements. Most DMMs will offer a variety of measurements and ranges. The basic measurements will include,

Current (DC & AC) Voltage (DC & AC)

• • •

Resistance

However, most DMM’s are able to offer additional tests. These may include some of the following,

Capacitance Diode Test Temperature

• • • • • •

Frequency

Transistor test

Continuity (buzzer)

Safety Precautions & Procedures

• Read the complete Owners Manual supplied with your Multimeter, know your equipment before use. • Inspect the multimeter, test leads condition/quality, terminal connections, etc. for any damage before use, to ensure safety and maintain accuracy, calibrate and check the meter at least once a year. • Damaged test probes cannot be repaired; they must be replaced. Never use damaged test probes. • Ensure all the adequate PPE is being used.

Safety Precautions & Procedures

• If you are not confident, testing a certain circuit, do some research before beginning tests.

• Never assume a meter is working properly. Use a known voltage source to verify.

• Before starting any measurement activity, you should check the multimeter for continuity. To do this, connect its leads and confirm that it reads zero or close to zero.

• The range or function switch should only be changed when the leads are disconnected from the circuit.

• Use test leads with minimal exposed metal at the tip to protect against electrical shorting

Safety Precautions & Procedures

• Know your circuit before testing, voltage sources, earths, etc.

• If you are unsure of which Range to choose, then start with the highest and work your way down

• Ensure that test leads are in the correct terminals before testing.

• When using probes, keep fingers behind the finger guards on the probes.

• Never check the resistance of an Airbag Unit as it could deploy the airbag.

Safety Precautions & Procedures

After care

• When not in use, make sure the multimeter is turned OFF.

• Always disconnect your leads from the multimeter and store both in a dry & safe place.

• It is not recommended to pierce the insulation on the wires with the probes but if you do, use clear nail varnish to seal the hole and avoid moisture ingress which would damage the wire.

DC & AC Voltage Measurement

• Set the function switch to Volts DC or AC depending on the circuit your testing.

• Plug the black lead into the COM jack and Red into V jack.

• If you do not know the approximate voltage range about to be measured, use the largest range available and work your way down.

• Connect the test probes to the circuit: Black to the earth and red to positive test point.

• Voltage is always measured in Parallel with the circuit.

Resistance Measurement

• Plug the black test lead into the COM jack and V jack.

• Set the function switch to ohms, check the internal resistance of your meter by joining the two probes and take note of the reading.

• Connect the red and black test leads ACROSS the device to be measured or if you are testing a wire, disconnect both ends of a wire and place the 2 probes each end of the wire.

• Resistance is always measured with the meter in Parallel with an open circuit.

Current Measurement

• Plug the black test lead into the COM jack and the red test lead into either of the Current jacks.

• If you do not know the current range about to be measured, use the 10 A jack and set the function switch to either DC Amps or AC Amps. • Break open the circuit at the point where you want to measure the current, connect your two probes in Series and then re-apply the power to the circuit.

• Turn the power off to the device before removing the meter from the circuit.

Clamp Ammeter Measurement

Clamp Ammeter Measurement

• Connect both leads to the meter, black to common and red to V terminal

• If the clamp includes a range setting, select the most suitable for taking the measurement.

• Set the multimeter range to V dc according to the selection made on the clamp ammeter. Normally an mV/A value is indicated. Zero the clamp ammeter, the clamp will have a button to do this.

• Position the clamp around the cable to be measured, remember the direction of the current when putting it into position.

• When the circuit is activated, you will see a V reading on the DMM, this must be converted according to the range chosen on the clamp to Amps.

Diode Testing

Diode has two terminals Anode (+) and Cathode (-). Terminals can be identified by the shaded portion or a ring at the end of the diode. Terminal near the shaded portion or ring is Cathode (-) and other one is anode (+).

1.

Turn the power off to the device and discharge any capacitors!

6.

Diodes are tested in Parallel .

7. Take note of the reading on the LCD, normally read around 0.5v – 0.8v.

2. Plug the black test lead into the COM terminal & the read lead into the V terminal.

3. Set the function switch to Diode test.

4.

Place the red lead on the Anode (+).

5.

Place the black lead on the Cathode (-).

Diode Testing

Diode has two terminals Anode (+) and Cathode (-). Terminals can be identified by the shaded portion or a ring at the end of the diode. Terminal near the shaded portion or ring is Cathode (-) and other one is anode (+).

Swap the leads on the diode and you should see “O.L” on the LCD

Frequency Measurement

Analogue Waveform

• Plug the black test lead into the COM terminal & red test lead into the V terminal. • Set the function switch to Hz (Hertz). • Place the black probe on a good earth. • Place the red probe on wire being tested. • Frequency is measured in Parallel . Frequency is measured using a unit called the Hertz to measure the number of cycles a waveform produces in a second. The number of Hertz is calculated by dividing the number of repeat cycles by the length of time in seconds.

Digital Waveform

2 cycles per second (2Hz)

Pulsed Signal Measurement

Known as Duty Cycle, describes the “On Time” for a pulsed signal. We can report duty cycle in units of time, but usually as a percentage.

• Plug the black test lead into the COM terminal & red test lead into the V terminal. • Set the function switch to Hz (Hertz). • Connect the test leads to the circuit to be tested in Parallel . • A positive symbol (+) indicates Positive time percent voltage measurement. • A negative symbol (-) indicates Negative time percent voltage measurement.

Duty cycle changing but the Frequency staying the same. This is known as Pulse Width Modulation (PWM)

Duty cycle staying the same but frequency changing

Temperature Measurement

For the measurement of temperature, a probe is required that is supplied in some multimeters as an addition. It can give a reading in Degrees Celsius or Degrees Fahrenheit.

Some temperature probe must be connected in a specific socket on the multimeters, or with an adapter it is fitted into the "COM“ & “V” multimeter terminals.

RPM Measurement

An inductive clamp is required to carry out this measurement, which an additional accessory.

• Connect the clamp's black lead to the "COM" terminal, while the red lead should be connected to the voltage terminal or a specific terminal.

Select “RPM” on your meter.

•

• Fit the clamp around a Plug Lead and start the engine.

Introduction To Oscilloscopes

The oscilloscope is a device that can graphically display the voltage of the circuit over time on a co-ordinate axis.

These co-ordinates are called

“Y” for signal voltage “X” for signal time.

Introduction To Oscilloscopes

Main Advantages of an Oscilloscope

• You can determine the time and voltage values of a signal. • You can calculate the frequency of an oscillating signal. • You can see the "moving parts" of a circuit represented by the signal. • You can tell if a malfunctioning component is distorting the signal. • You can find out how much of a signal is direct current (DC) or alternating current (AC). • You can tell how much of the signal is noise and whether the noise is changing with time

There are two types of oscilloscopes, Analogue and Digital .

Analogue Oscilloscope

An Analogue Oscilloscope is based on the movement of a light point over a cathode-ray tube screen in real time, this movement causes a light beam that remains temporarily on the screen as if it were tracing a line.

Therefore, its image cannot be displayed continuously as the trace moves from left to right on the screen.

The main problem of this type of oscilloscope lies in very low or high frequency signals, as when tracing in real-time the light beam is not displayed or is illegible.

Digital Oscilloscope

Digital Oscilloscopes have replaced the analogue devices, as these, by means of an analogue/digital converter, are capable of storing the sampling signal and later reconstructing it in order to properly display it on the screen. To reduce costs without losing a significant amount of performance, there are PC based oscilloscopes.

They come in a large variety with a great difference in price, the most important variables being:

• Analogue/digital converter type. • Sampling rate. • Memory capacity. • Number of channels. • Type of screen.

Technical Characteristics

The most important characteristics are:

• The sampling rate or frequency.

Bandwidth

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The input sensitivity.

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• The number of available channels.

The maximum input voltage.

•

The horizontal scale.

•

Technical Characteristics

The sampling rate or frequency is exclusive to digital oscilloscopes, as these have an analogue/digital converter. These samples, depending on their size and rate, allow the details of the signals to be better represented.

Bandwidth indicates the range of frequencies that can be measured with precision. It is measured in MHz and the larger it is, the better the resolution on the screen.

Technical Characteristics

Input sensitivity This is the minimum voltage range that can be displayed on the screen, therefore if the signal oscillates under this value, it cannot be displayed (usually between 2 mV and 100 mV per division). Number of channels In the automotive sector, a minimum of two channels are required although four is ideal. Scopes with several channels, the quantity and type of analogue/digital converter used can influence the sampling rate when several channels at the same time are used. Maximum input voltage is the maximum input voltage that should enter through the oscilloscope channel in order not to damage it. The use of an inserted accessory is required to avoid this problem.

Horizontal scale gives the minimum and maximum time that can be displayed on the same screen.

Oscilloscope Leads

Conventional leads and Attenuation leads/adapters,

Attenuation leads and adapters are used to display high-frequency signals that standard equipment is not capable of displaying correctly. It “downsizes” readings that would not normally be possible to display.

You can buy attenuation leads or your other option is to buy an attenuation adapter which allows you to use conventional leads.

Manual Selection switch on probe

20:1 attenuation adapter (multiply reading by 20)

Oscilloscope Clamps

The clamp ammeter These are used for measuring the current that flows through the cable under test. As it does not have direct contact with the installation, it causes very little interference to the signal. These work the same way as described previously in the “Multimeter Measurement” section except some oscilloscopes have the ability to convert the V reading into Amps.

Inductive clamp

This is usually used to display ignition signals by fitting it on the high voltage cable of cylinder number 1. Current that flows through it causes a current pulse due to induction in the winding in it. This voltage peak is used as a synchronisation trigger by the oscilloscope.

Oscilloscope Clamps

Capacitive clamp

This probe is used for the display of the ignition secondary; it should be fitted directly on the high voltage cable to the plug or on the high voltage cable that goes from the coil to the distributor.

Oscilloscope Lead Extras

To avoid damaging the electrical insulation of the wire, it is very important to choose the correct test clamps and probes. Also using the correct test clamp or probe will make testing easier and more accurate.

You can purchase additional devices such as:

• Back probe pins. • Small and large alligator clips. • Piercing probes.

Basic Concepts

It is important to know the types of signals there are, irrespective of whether it is a direct or alternating current. There are basically three types of signals:

Sinusoidal/Sine, With a waveform normally due to slow changes of the voltage level.

Square, Also commonly called digital, as there are two voltage levels and the change between both occurs very quickly.

Triangular – (not common in Automotive), It is only an instant at its maximum voltage level, therefore it forms rising peaks that can form two of a triangle.

Basic Concepts

Amplitude This is the maximum voltage level that the signal can reach. It should be remembered that in some cases it can be negative. Peak to peak voltage In alternating sinusoidal signals, the peak-to-peak voltage is considered as the maximum voltage differential value. Dwell This is the percentage of time in which the signal remains with its voltage level near to ground with respect to the duration of one cycle. It is measured in %, a value of 100 % corresponds to a direct voltage of 0V or ground, and 0% to a direct positive voltage.

Basic Concepts

Duty Cycle The duty cycle is the cycle or working time of an actuator activated by a pulsed current and corresponds to the percentage of the cycle in which there is a potential difference at the actuator. Frequency This is the number of cycles in a specific time. It is measured in hertz (Hz). A hertz corresponds to a signal in which there is one cycle per second.

Cycle A cycle is a complete signal, which is repeated periodically in time.

Period The period is the duration of the complete cycle.

Basic Concepts

Edges They can be rising or falling, in which the signal moves between two voltage points with a different value. Valley Voltage The valley voltage is the voltage that exists at the end of a falling edge of a signal, for example in a voltage drop. PWM or RCO A PWM (Pulse Width Modulation) signal has a fixed signal frequency and a variable dwell percentage.

Main Settings

Setting the voltage level This setting changes the size of the signal on the vertical Y axis, with the intention of making the entire signal visible on the screen.

20V setting

5V setting

Main Settings

Setting the time Set the divisions in order to see the image wider or narrower. An increase of the "Time/Division" leads to a narrower image and vice versa.

100ms divisions

500ms divisions

Main Settings

Setting the Trigger

The trigger controls let you stabilize repeating waveforms and capture single-shot waveforms.

The trigger makes repeating waveforms appear static on the oscilloscope display by repeatedly displaying the same portion of the input signal.

Trigger

Voltage Over Time

A waveform is simply a graph of voltage plotted against time .

Voltage

Time

PicoScope vs Live Data

Accelerator Pedal - Live data capture, both tracks.

Typical example of a serial diagnostic live data stream, but in reality, this is anything but live, and only a scan tools interpretation of signals that have been filtered multiple times.

PicoScope vs Live Data

With PicoScope however . . .

PicoScope vs Live Data

With PicoScope you can;

Be sure to see an absolutely live image of the component working

View both tracks on the same screen

Identify intermittent faults

Zoom in to view every detail

PicoScope 6 Software

Pico software is free to download, and there are no annual fees.

Works on any windows-based PC, laptop or tablet.

Demo mode available before purchasing a scope to explore and understand how to use the system.

PicoScope 6 Software

Pico Diagnostics

Alongside Pico’s oscilloscope software, they also provide a diagnostic software package that includes some advanced testing procedures, including :

Compression

• • • •

Battery and Alternator Propshaft Balancing

Cylinder Balance

• Noise Vibration and Harshness

Pico Diagnostics

Pico Diagnostics test procedures are Wizard driven and allows the user to unobtrusively analyse and test vehicle systems in a user-friendly manner. The above shows the helpful wizard lead tests, guiding the user through the correct connection and the conditions to run the test. A test report is also produced showing compression levels (in our example) of an eight-cylinder engine all to be within tolerance.

All test reports can be saved, shared and printed for customer information.

Connecting to Components

Pico Scope kits come with a variety of accessories to help make connecting to vehicle components simple and more importantly, non-intrusive. This allows capturing signals to be done without removing components or damaging vehicle wiring.

Current clamps

Breakout leads

Back-pinning probes

COP probe

Capturing Waveforms

Once connection to the component is made it’s easy to capture a waveform using PicoScope software

To capture data, remember:

• The scope must be connected to the Laptop or PC with the LED active • Locate the components signal wire • If a current clamp is used, ensure it is switched on and turned the right way around • The vehicle ignition is on and for some tests the engine is running • Always press Go on the scope screen

Using Guided Tests

PicoScope software has over 150 guided tests to help the user connect, capture and analyse data;

Connection info

• • •

Example waveform

Waveform analysis help

Also by selecting a guided test, the software sets the scope settings to run the chosen test

Testing Compression

Pico Diagnostics Compression Test

The easiest way to view a potential compression issue on one cylinder is running a relative compression test using our PicoScope diagnostic software.

As with all the tests contained within Pico Diagnostics there is a wizard to guide you through the test.

This helps you to connect to the vehicle correctly and run the test.

Pico Diagnostics Compression Test

The beauty of the Pico Diagnostic software is giving the technician a simple and clear result that can either pinpoint an issue for further investigation or eradicate a suspected issue.

The test will run on any vehicle with up to 12 cylinders and give the technician a clear bar graph highlighting any issues – suspect cylinders would be shown in red. As with all PicoScope files, you can save, share and print out a copy for your customer prior to any work being undertaken.

Pico Diagnostics Compression Test

This information is simply a graphed result of a relative compression test that you could perform with our PicoScope software. However showing a customer this raw data view can really back up the bar graph showing the clean saw tooth pattern we would expect to see in compression.

Further Testing with WPS500X

Further Compression Testing with WPS500X

If following your relative compression testing using Pico Diagnostics a compression issue is found, further testing and analysis should be carried out using our WPS pressure transducer.

Consider this an X-ray machine for your engine.

Running Compression (Petrol) Connection

WPS500X: How is it used?

Running Compression Waveform (Petrol)

Running Compression Waveform (Petrol)

Running compression waveform (Petrol)

Compression Towers Must be Equal

Compression Tower

Compression Tower

Expansion and intake pockets must be equal in depth

So knowing all this it would be easy to spot the cause of a compression problem before an expensive engine strip down?

So what's going wrong here? Engine runs uneven and severe misfire present

Cam/Crank Synchronisation

Cam Crank Synchronisation

Details of how to connect to individual components are available in PicoScope guided tests, but here are some tips for capturing Cam/Crank signals:

• Set your timebase over an extended period – we’ve used 50 ms/div • Use the Zoom function to view the detail

• A consistent pattern for both cam and crank signals • The ability to even count the teeth on the flywheel

Cam Crank Synchronisation

Start by capturing Cam and Crank signals together, you should see a pair of waveforms something like the image to the left.

With a little knowledge it is easy to start deciphering these signals.

Cam Crank Synchronisation

Camshaft signal (Red)

To understand how this relates to the crank signal, we must first identify a pattern.

In this case note the purple arrows, and gaps – large – large –small – small – large-etc.

Cam Crank Synchronisation

The Crankshaft signal will give us a clear 720° of revolution of our engine.

So now we have a reference of a good known timing waveform between the Cam and Crank sensor.

Cam Crank Synchronisation

Remember our cam signal and our big – big – small – small gaps?

Note how our crank sensor waveform lines up alongside the end of the last small gap in the cam sensor pattern. This gives us an absolute reference for this engine .

Cam Crank Synchronisation

With PicoScope can you view this data in so much detail.

Use the zoom function and our built- in software rotation rulers to help with analysis

Component tested:_________________________________________________________

Y

X t/div__________________________

Y v/div__________________________

X

Thank you for your time, Any questions?