Scope / Multimeter
General Reference
41
3.13.3 Troubleshooting Signals
When capturing signals, you may occasionally encounter problems with the way
the signal initially displays. Noise, hash, 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.
•
Make sure you have the correct test leads connected to the applicable test
point(s) and test lead jacks on the diagnostic tool.
•
Ensure the signal and ground connections are clean and secure, at the test
points and diagnostic tool.
•
Ensure the polarity of the test leads connections are correct.
•
If using stackable connectors, try to isolate or only connect the leads being used
to capture the signal.
•
Make sure the ground lead is providing a direct ground from the circuit to the
diagnostic tool test lead jack.
•
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.)
•
Use the shortest test leads possible.
•
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.
•
Check the test lead or probes for damage.
•
Enable or disable channel controls also to help try and clean the signal:
–
—maximizes sampling rate, but may pickup unwanted noise
–
—removes signal noise or interference
–
—switches signal polarity
–
—blocks the DC portion of signal
–
—provides a more accurate measurement on select GMM tests
where noise is present
–
Scale (Vertical scale adjustment)
—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
•
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 scale adjustment)
•
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 (Horizontal or Time scale adjustment)
.
•
Move the zero baseline marker to move the zero baseline of the signal vertically
on the screen to the desired position. See
.
•
Check calibration of test leads or probe(s) if applicable. See
.
3.13.4 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
10
3
or 1,000
(M) mega
10
6
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
