Pressure Sensors changes periodically. Similar to the
thermal sensitivity change the output
signal gives a wrong pressure value
due to change of temperature. The
maximum misreading within one cycle
due to this thermal effect is called
cyclic temperature drift or thermal
shock error.
The cyclic temperature drift is one of
the most significant parameters for
thermodynamic analysis. This is due
to the fact that it acts over a large
crank angle range. The influence on
parameters that are integrated over
one cycle (e.g. the indicated mean
effective pressure IMEP) is therefore
significant. Consequently a smaller
cyclic temperature drift results in a
higher accuracy of the measurement.
It is crucial how the procedure to
measure this value is defined. At the
moment there exists no standard
procedure which defines under
which conditions the cyclic drift
has to be measured. This makes a
direct comparison between values
of different manufacturers almost
impossible. At AVL the measuring
conditions are chosen in that way
that they are as critical as possible.
The values given in this catalog are
measured on a DI diesel engine at
1300 rpm and an IMEP of 7 bar. The
choice of the combustion engine
type for the determination of cyclic
drift is significant. In addition to the
AVL standard values Δp is also stated
in order to allow comparisons with
sensors from other manufacturers.
This value is measured at 9 bar IMEP
and 1500 rpm on a typical gasoline
engine.
E
Eccentricity mm
In a standard spark plug the center
electrode is exactly in the axial
middle of the spark plug. Sparkplugs
with diameter M10 and integrated
pressure sensor require a small eccentricity
of the electrode due to the
limited available space.
Electric strength V
Based on the design of the center
electrode the electric strength indicates
the maximum electric voltage
capability of the spark plug.
Electrode gap mm
The optimal electrode gap of a spark
plug is determined by the gap of the
original spark plug.
The maximum electric strength of
the spark plug defines the maximum
possible electrode gap of the measurement
spark plug. The electrode
gap must be adjusted according
to the final compression pressure
(FCP) from the compression stroke.
This is a convenient metric which is
roughly proportional to the voltage
demand required to jump the gap.
For detailed instructions please refer
to the document AT4370E which can
be requested from your technical
sales support or downloaded from
our website.
The maximum electric strength of
the new generation of spark plugs
(ZI22, ZI33 and ZI45) is high enough
(45 kV) to use the same gap as the
original spark plug.
F
Front sealed
Front sealed sensors have the sealing
surface at the rim of the sensor
membrane. This kind of sealing
prevents deposits in the thread and
can be important for long time monitoring
installations. Front sealed
mounting requires always a recessed
mounting. Depending on the
mechanical strength of the cylinder
head the recessing of the membrane
results in an indicating channel. If the
dimensions of this indicating channel
are not well chosen, pipe oscillations
can occur. This physical effect can
limit the signal quality during the
measurement. On the other hand
front sealed sensors show in principal
a better thermal conductivity
to the cylinder head than shoulder
sealed sensors and can reduce
thermal effects and improve signal
precision. Shoulder sealed sensors
seal at the upper end of the housing
which results in almost no mechanical
stress on the membrane. It allows
also a flush mounted membrane
which eliminates the chance for pipe
oscillations.
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