Advanced Automotive Fault Diagnosis

tải về 7.07 Mb.

Chế độ xem pdf

trang	52/299
Chuyển đổi dữ liệu	12.10.2022
Kích	7.07 Mb.
	#53540

1 ... 48 49 50 51 52 53 54 55 ... 299

Advanced Automotive Fault Diagnosis
LÔØI NOÙI ÑAÀU, ledklok

4.2.6 Hall effect distributor pick-up waveform Hall sensors are now used in a number of ways. The ignition distributor is very common but they Figure 4.9

4.2.5 Coolant temperature
sensor waveform
Most coolant temperature sensors are NTC ther-
mistors; their resistance decreases as tempera-
ture increases (Figure 4.9). This can be measured
on most systems as a reducing voltage signal
(Figure 4.10).
The coolant temperature sensor (CTS) will
usually be a two wire device with a voltage sup-
ply of approximately 5 V.
The resistance change will therefore alter the
voltage seen at the sensor and can be monitored
for any discrepancies across its operational range.
By selecting a time scale of 500 seconds and con-
necting the oscilloscope to the sensor, the output
voltage can be monitored. Start the engine and in
the majority of cases the voltage will start in the
region of 3 to 4 V and fall gradually. The voltage
will depend on the temperature of the engine.
The rate of voltage change is usually linear
with no sudden changes to the voltage, if the sen-
sor displays a fault at a certain temperature, it
will show up in this test.
4.2.6 Hall effect distributor
pick-up waveform
Hall sensors are now used in a number of ways.
The ignition distributor is very common but they
Figure 4.9 Temperature sensor

Oscilloscope diagnostics
45
are also used by ABS for monitoring wheel speed
and as transmission speed sensors, for example
(Figure 4.11).
This form of trigger device is a simple digital
‘on/off switch’ which produces a square wave out-
put that is recognised and processed by the igni-
tion control module or engine management ECU.
The trigger has a rotating metal disc with open-
ings that pass between an electromagnet and the
semiconductor (Hall chip). This action produces
a square wave that is used by the ECU or ampli-
fier (Figure 4.12).
The sensor will usually have three connections
which are: (1) a stabilised supply voltage, (2) an
earth and (3) the output signal. The square wave
when monitored on an oscilloscope may vary in
amplitude; this is not usually a problem as it is
the frequency that is important, not the height of
the voltage. However, in most cases the amplitude/
voltage will remain constant.

tải về 7.07 Mb.

Chia sẻ với bạn bè của bạn:

1 ... 48 49 50 51 52 53 54 55 ... 299