4.12
Engine RPM – Tachometer
Daqu — Manual
Variable-reluctance (magnetic) pickup
sensors are also sometimes used.
They give lower voltage spikes and they shall also be connected to the
Z channel.
Active inductive (Hall effect)
sensors have a clean signal and shall be
connected to Y channel.
Number of pulses per one engine RPM must be also known. Some engines
have only one sensor pulse per one RPM, some have two pulses and some can
have much more.
When reduction gearbox is attached to an engine, propeller PRMs are smaller
than engine RPMs. When reduction ratio is provided, Daqu emits propeller
RPMs instead of engine RPMs. Usually, the reduction ratio is 1.0, which
means that engine RPMs are emitted.
Let
N
denotes number of pulses per RPM,
T
denotes time between pulses
measured in seconds and
R
denotes reduction ratio.
N
and
R
are given by
configuration and
T
is measured by Daqu. Output RPM is then calculated
as:
RPM =
60
N
·
T
·
R
4.12.1
Z Channel
Trigger coil and variable-reluctance pickup sensors connect to the Z channel.
Schematics shown on Figure 24 illustrates the connection principle.
Table 17 shows appropriate settings for Rotax 912 engine.
Pulses
is set to
one as there is only one pulse per RPM.
Prop reduction
value is set to one –
no reduction is applied and output value will be engine RPMs.
4.12.2
Y Channel
When active inductive (Hall effect) sensors are used, signal shapes are much
more polite and Y channel shall be used to handle them.
Connection schematics were already given in section 3.8. Two schematics
were given, one for NPN sensor, Figure 13 and the other for PNP sensor,
Figure 14.
Sensors often do not specify wheather they are NPN or PNP types. Trial
and error may be used here. Connect the sensor first as NPN and of there is
©
Kanardia
2019
42
