DAF LF45, LF55 Series. Manual — part 338
5
LF45/55 series
General
COMPONENTS
1-1
1. GENERAL
1.1 MULTIMETER
The Fluke 87 multimeter allows you to select
various measuring options:
Units of measurement
The multimeter should be set to the range for
the unit of measurement required.
For example, the voltage, current or resistance
range.
The units of measurement are indicated by
symbols on the meter. The following symbols
are used.
1.
DC voltage
2.
AC voltage
3.
DC current
4.
AC current
5.
resistance
6.
duty cycle
7.
frequency
DCV - V
ACV - V
DCA - A
ACA -A
Ohm -
%
Hz
1
2
3
4
5
6
7
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COMPONENTS
General
LF45/55 series
1-2
1.2 SCOPEMETER
Diagnostics in modern electronic systems is
steadily becoming more complex.
Using a multimeter on its own is not always
sufficient to diagnose a fault.
The scopemeter allows complex signals to be
measured.
Practical examples of complex signals are:
-
PWM signals
-
deformation of signals
-
CAN-bus signals
1.3 SIGNAL MEASUREMENTS
Sine-wave signal (AC voltage)
This signal regularly changes polarity with
respect to the “0” line
+
-
0
Frequency
The frequency is shown in Hertz (Hz).
The number of complete sines per second is the
frequency of the signal (3 Hz in the diagram).
t = 1 second
+
-
t
1
2
3
0
Voltage
If the number of sines per second increases, not
just the frequency increases but also the
voltage. This depends on the type of sensor.
+
-
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LF45/55 series
General
COMPONENTS
1-3
Measuring a sine-wave signal
The sine-wave signal can be measured in the
following ways using a multimeter:
-
with the multimeter in the frequency
(Hz) position.
In this way, the number of complete sines
per second is measured.
-
multimeter in the AC voltage position.
In this way, the average value of the
supplied voltage is measured.
Sine-wave signals in the vehicle
-
Wheel speed sensor output signal
-
Engine speed sensor output signal.
Square-wave signal
Square-wave signals are signals with only two
voltage levels, both of which have the same
duration in principle (t1 is equal to t2).
+
0
t
2
t
1
If the duration is different for the two levels (t1 is
not equal to t2), the signal is also called “pulse
train”.
t
1
t
2
0
+
Duty cycle
The duty cycle is the ratio between the two
voltage levels, expressed as a percentage.
A
x 100%
B
x 100%
The voltage level ratio of a pulse train may
change (for example, when the vehicle speed
increases).
A
B
0
+
Voltage
If the duty cycle increases, the average voltage
will also increase.
0
+
A
B
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COMPONENTS
General
LF45/55 series
1-4
Measuring a square-wave signal
The square-wave signal can be measured in the
following ways using a multimeter:
-
with the multimeter in the duty cycle
(%) position.
In this way, the voltage level ratio is
measured.
-
multimeter in the DC voltage position.
In this way, the average value of the
supplied voltage is measured.
Square-wave signals in the vehicle
-
Output signal of the vehicle speed sensor
-
Vehicle speed signal from tachograph to
electronic units
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