General_Reference_

General Reference (Testing Strategies)

When conducting automotive diagnostics, situations may arise when you need to capture and analyze a signal that you are not familiar with, do not know what the intended waveform pattern should look like, or even how to set the scope to acquire the signal.

The following tips are intended to provide guidance, at the most basic level to assist you in your lab scope diagnostics.

Testing information and/or procedures for testing certain components may be available in the Guided Component Test function, see Guided Component Tests for additional information. If you have already narrowed down the system and/or component to test, ID the vehicle within the Guided Component Test function, and check the available tests first, as this may save you some time.

If the Guided Component Test function, does not have the test you are looking for, you need to determine are few thing about what you are testing to get the scope / meter set up to capture a signal or make a measurement.

Testing information and known good waveform libraries may also be available from other sources (e.g. ShopKey Pro or other online sources). Obtaining correct testing reference information can be a key advantage in making sound repair decisions.

Listed below are a few basic questions to help narrow down the testing direction to follow.

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Are you looking to make or test a simple voltage or current level or maybe check resistance or continuity? Then you may want to use the DMM.

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Are you looking to check a circuit/component for an erratic dropout or make a frequency test? You may want to use the GMM.

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Do you need to see signal details (level, shape, frequency etc.)? The lab scope may be the best choice.

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Are you testing a DC or AC signal?

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What is the operating range of the circuit?

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Do you know what type or shape the intended waveform should be?

After answering the previous questions (at a minimum), you need to determine which Scope / Multimeter test function you are going to use (e.g. Lab Scope, DMM or GMM). See Tests and Capabilities (Quick Reference Chart).

Once your test function is selected, you can now connect the test leads and select the applicable probe and scales:

Probe (test) type, see Probe Icon

Vertical scale, see Scale (Vertical / Y-axis)

Sweep scale, see Sweep Scale (X-axis)

Connect the test leads or probe, to the applicable test point(s). Always use the correct lead or probe designed for the test and ensure the signal and ground connections are clean and secure.

For the initial setup, you may wish to turn other channel settings off (e.g. Peak, Filter, Invert, AC Coupling, Threshold etc.), as these may affect the signal display. See Control Panel and Settings.

As a default setting, trigger is normally off. The scope/meter uses internal circuitry to display a signal if present. However, in certain circumstances additional channel adjustments may be required, or the trigger mode may have to be turned on, for a signal that is present but not displayed. You may also need to readjust the vertical scale if set to low, in order to bring the signal into the viewable display area.

At this point you should have a visible signal on the screen. An ideal signal should be displayed within the area of the display.

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If the signal goes beyond the top and bottom of the display, try and readjust the vertical scale to a higher setting, to bring the signal into the viewable display area.

Use the zero baseline controls or move the zero baseline marker onscreen to move the zero baseline of the signal vertically on the screen to the desired position. See Zero Baseline Adjustment.

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If the signal cycles are compressed (close to each other), try and readjust the sweep scale (horizontal scale) to a lower setting to display less cycles.

Once you have a usable signal displayed, if needed use the trigger function to stabilize a changing or erratic signal (a signal that may flicker or drift), so that it is easier to view. Try and set the trigger at the mid-point of the signal, and then adjust as needed from there. See Triggers.

As all signals are different, and due to other variables, additional adjustments may be needed to get the signal displayed exactly how you need. Review the channel settings section in this manual for additional information on using the settings. See Control Panel and Settings.

At this point you should have a signal displayed that will allow you to see the overall signal characteristics, and allow you to begin your diagnosis.

Comparing your captured waveforms to known good waveforms, can be a time saver and provide supporting evidence when trying to determine a fault. See the next section for additional information.

Troubleshooting Signals

When capturing signals, you may occasionally encounter problems with the way the signal initially displays. Noise, hash and fuzz are some of the terms used to describe unwanted signals displaying in or on the signal you are trying to capture, basically making the signal unclear. The following tips are intended to provide some basic guidance, to help resolve these types of issues if encountered.

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Make sure you have the correct test leads connected to the applicable test point(s) and test lead jacks on the diagnostic tool.

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Ensure the signal and ground connections are clean and secure, at the test points and diagnostic tool.

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Ensure the polarity of the test leads connections are correct.

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If using stackable connectors, try to isolate or only connect the leads being used to capture the signal.

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Make sure the ground lead is providing a direct ground from the circuit to the diagnostic tool test lead jack.

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Isolate the test leads from other components, leads, or systems that may induce unwanted noise into the signal being tested (e.g. electric motors, secondary ignition components, relays, alternators, etc.)

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Use the shortest test leads possible.

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Try different test leads, to verify the issue. Use the recommended snap-on leads or probes available for the diagnostic tool or equivalent. Shielded test leads are recommended.

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Check the test lead or probes for damage.

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Enable or disable channel controls also to help try and clean the signal:

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Peak Detect Icon—maximizes sampling rate, but may pickup unwanted noise

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Filter Icon—removes signal noise or interference

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Invert Icon—switches signal polarity

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Coupling AC Icon—blocks the DC portion of signal

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Threshold Auto/Manual (GMM Only)—provides a more accurate measurement on select GMM tests where noise is present

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Scale (Vertical / Y-axis)—adjusts vertical scale. Using a higher setting may provide a cleaner signal in some situations.

For signals that do not display or display off the screen, erratic, compressed etc.:

Use a trigger to help stabilize the signal. Try and set the trigger at the mid-point of the signal, and then adjust as needed from there. See Triggers.

If the signal wraps off the top and bottom of the display, try and readjust the vertical scale to a higher setting, to bring the signal into the viewable display area. See Scale (Vertical / Y-axis).

If the signal cycles are compressed (close to each other), try and readjust the sweep scale (horizontal scale) to a lower setting to display less cycles. Try a higher setting if the cycles are spread too far across the screen and seem flat. See Sweep Scale (X-axis).

Move the zero baseline marker to move the zero baseline of the signal vertically on the screen to the desired position. See Zero Baseline Adjustment.

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Check calibration of test leads or probe(s) if applicable. See Test Lead / Probe Calibration.

Units of Measurement / Conversions

Base Units
(Symbol) / Unit Prefix	Typical Expressions
(µ) micro	0.000001 or 10-6 or 1/1,000,000
(m) milli	0.001 or 10-3 or 1/1,000
(c) centi	0.01 or 10-2 or 1/100
(k) kilo	103 or 1,000
(M) mega	106 or 1,000,000

Electrical Units
(Symbol) / Description	Equivalents
(V) Voltage	V = I × R
(I) Current	I = V ÷ R
(R) or (Ω) Resistance	R = V ÷ I
(Hz) Frequency	ƒ(freq.) = 1 ÷ T(time) or 1 cycle per second
Voltage
(µV) microvolt	1 µV = 0.000001 V
(mV) millivolt	1 mV = 0.001 V
(V) volt	1 V = 1000 mV
(kV) kilovolt	1kV = 1,000 Volts.
Ohms
(mΩ) milliohm	1 mΩ = 0.001 ohms
(Ω) ohm	1 Ω = 1000 mΩ
(kΩ) kiloohm	1 kΩ = 1000 Ω
(MΩ) megaohm	1 MΩ = 1,000,000 Ω
Amperes
(µA) microamps	1 µA = 0.000001 amps
(mA) milliamps	1 mA = 0.001 amps
(A) amps	1A = 1000 mA
(ka) kiloamps	1 ka = 1000 amps
Frequency
(MHz) megahertz	1 MHz = 1,000,000 Hertz
(kHz) kilohertz	1 kHz = 1000 Hertz

Pressure Units
(Symbol) / Description	Equivalents
(psi) pounds per square inch	1 psi = 6894.757 Pa 1 psi = 0.06894757 bar 1 psi = 2.036021 inHg
(bar)	1 bar = 14.50377 psi 1 bar = 100000 Pa 1 bar = 29.52999 inHg
(Mbar) Millibar	1 Mbar = 0.001 bar
(Pa) pascal	1 Pa = 0.0001450377 psi 1 Pa = 0.00001 bar 1 Pa = 0.0002952999 inHg
(kPa) KiloPasca	1 kPa = 1000 Pa
(MPa) Megapascal	1 MPa = 1,000,000 Pa
(inHg) inches of mercury	1 inHg = 0.03386388 bar 1 inHg = 0.4911541 psi 1 inHg = 3386.388 Pa

Pressure Conversions
psi x 0.0689 = bar
psi x 6.8950 = kPa
psi x 0.0703 = kg/cm²
bar x 14.5030 = psi
bar x 100.0000 = kPa
bar x 29.5300 = inHg (60°F)
kPa x 0.1450 = psi
kPa x 0.0100 = bar
kPa x 0.0102 = kg/cm²
kPa x 0.295299 = inHg
kg/cm² x 98.0700 = psi
kg/cm² x 0.9807 = bar
kg/cm² x 14.2200 = kPa
inHg (60°) x 0.0333 = bar
inHg (60°) x 3.3770 = kPa
inHg (60°) x 0.0344 = kg/cm²
inHg x 25.4 = mmHg
mmHg x 0.003994 = inHg

Temperature Units
(Symbol) / Description	Conversions
(°C) degree Celsius	°C = 0.556 x (°F - 32)
(°F) degree Fahrenheit	°F = (1.8 x °C) + 32

Time Units
(Symbol) / Description	Equivalents
(µs) microsecond	1 µs = 0.000001 of a second
(ms) millisecond	1 ms = 0.001 of a second
(s) second	1 s = 1000 ms

Duty % to Dwell Conversions
Duty Cycle	Dwell
%	4 cyl	6 cyl	8 cyl
10	9.0	6.0	4.5
20	18.0	12.0	9.0
30	27.0	18.0	13.5
40	36.0	24.0	18.0
50	45.0	30.0	22.5
60	54.0	36.0	27.0
70	63.0	42.0	31.5
80	72.0	48.0	36.0
90	81.0	54.0	40.5
100	90.0	60.0	45.0

Glossary of Common Terms

Term / Abbreviation	Description
AC	Alternating Current - electrical current that switches polarity at regular intervals.
Aliasing	An effect that causes an incorrect signal to be displayed and/or causes a trigger to malfunction, due to the input signal exceeding the sample rate of the scope.
Amperage	The strength of an electric current, expressed in amperes
Amplitude	Vertical magnitude (level or position) of a signal, or the varying quantity from its zero value.
Buffer	An electronic reservoir for temporary storage of data.
Cursor	Onscreen markers used to measure time, amplitude and frequency.
Coupling AC	Function used to subtract the average value of a signal so that small variations can be displayed in the waveform.
DC	Direct Current - electrical current that flows in one direction only.
Delta	Difference in time between two events.
Dropout	An intermittent or unwanted, vertical fall in a signal to zero that may cause an undesired result.
Duty cycle	Measurement of the length of a signals on time. Specified as a percentage (ratio), of the total cycle time.
Dwell	Used to measure a signals on time in degrees of dwell. Commonly used to measure mixture control solenoids on carbureted feedback engines and specified in duty cycle %.
Dwell 60	Measurement of the length of a signals on time displayed on a 0 to 60 degree scale. 0° = 0%; 30° = 50%; 60° = 100%.
Dwell 90	Measurement of the length of a signals on time displayed on a 0 to 90 degree scale. 0° = 0%; 45° = 50%; 90° = 100%.
Filter	Function used to filter or smooth out spikes and fast variations in signals.
Frequency	The number of times a signal repeats in one second. Measured in Hertz (cycles per second).
Glitch	An intermittent or unwanted, error in a signal that may cause a false or undesired result.
Grid	The graph displayed on the scope screen that is made up of the x and y axis scales that aid in the measuring of signal characteristics.
Horizontal Scale	See Sweep Scale
Invert	Function used to switch signal polarity.
Lambda (l)	Used to represent a numerical value denoting the actual measured air/fuel ratio with respect to the ideal air/fuel ratio at stoichiometry. Lambda equals one (1) when the actual air/fuel ratio is equal to the theoretical (stoichiometric) air/fuel ratio of 14.7 (14.66) to 1. Lambda less than 1 means excess fuel; greater than 1 means excess air.
Megasamples per second (MS/s)	Sample rate unit equal to one million samples per second.
Noise or Hash	Unwanted voltage, current or signal interference that is imposed on a signal.
Parasitic Voltage	Trace voltage in a circuit after the main power source is disconnected.
Peak	The maximum amplitude value present in a varying or alternating voltage. This value may be either positive or negative.
Peak Detect	Peak detect captures and evaluates all signal sample points, in order to display fast occurring events or glitches.
Pressure Transducer	Electronic device that converts pressures (negative/positive) to electrical signals.
Pulse	A signal with abrupt (fast) signal direction changes in a positive or negative direction, with consistent level and duration.
Pulse Period	One complete on and off cycle or time period.
Pulse Train	Collection of signal pulses traveling together.
Pulse Width (duration)	Measurement of a signals on time in a circuit that pulses on and off. Specified in units of time.
Pulse Width Modulation (PWM)	A signal that continuously cycles on and off while the on-time varies within each cycle.
RMS	The RMS (root mean square) value of alternating currents and voltages is the effective current or voltage applied, rather than the peak current or voltage measurable. The AC RMS voltage value can be defined as the equivalent DC voltage of the AC voltage measured. RMS values are commonly used in AC electrical measurement, as they are more representative of DC measurements.
Sample Rate	Number of times (frequency) the scope/meter takes a sample of the signal. Specified in mega samples per second (MS/s).
Sampling	Process of obtaining a sequence of instantaneous values for a signal at regular or intermittent intervals. When a quantity of samples are collected the operational status of the device is determined.
Screen Update Rate	How often the captured data is (updated) displayed on the screen.
Signal	Detectable voltage, current, or magnetic field, by which specific information is transmitted in an electronic circuit or system.
Square Wave	A square or rectangular waveform (digital) which alternately switches high to low (on/off) for specific lengths of time, that has very fast rise and fall times.
Sweep Scale	The horizontal scale on the grid. Also referred to as time scale or x axis.
Threshold	The threshold function automatically sets a trigger and determines a threshold level in the middle of the signal range (calculated from the Min and Max measurements) to be used as a reference point to calculate the measurement.
Trace	The actual visible line displayed on the scope screen.
Trigger	A conditional function that initiates if and when a trace is drawn on the screen.
Trigger Slope	The slope that a trigger source signal must reach before the trigger circuit initiates a sweep.
VAC	Volts Alternating Current.
VDC	Volts Direct Current.
Vertical Scale	The vertical scale on the grid or (y-axis) represents what is being measured (voltage, amperage, pressure etc.), and the unit of measurement it is being measured in.
Volt	Unit of electric potential difference.
Voltage	Electromotive force or potential difference, expressed in volts.
Voltage (inductive) Kick	A voltage, many times higher than the applied voltage, produced by the collapsing magnetic field in a coil when the current through it is abruptly terminated.
Waveform	The graphic representation (form) of a signal over time, which the trace displays on the screen.
Zero Base Line	Reference setting or 0% level of a graph scale.