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Motorola Sensor Device Data
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Pressure Sensor FAQ’s
We have discovered that many of our customers have
similar questions about certain aspects of our pressure
sensor technology and operation. Here are the most
frequently asked questions and answers that have been
explained in relatively non–technical terms.
Q. How do I calculate total pressure error for my
applications
A. You can calculate total error in two fashions, worst case
error and most probable error. Worst case error is taking
all the individual errors and adding them up, while most
probable error sums the squares of the individual errors
and then take the square root of the total. In summary,
Error (Worst Case) = E1 + E2 + E3 + ... + En, while Error
(Most Probable) = SQRT[(E1)2 + (E2)2 + (E3)2 + ...
(En)2]; Please note that not all errors may apply in your
individual application.
Q. What is the media tolerance of our pressure sen-
sors
A. Most Motorola pressure sensors are specifically de-
signed for dry air applications. However, Motorola now
offers an MPXAZ series specifically designed for im-
proved media resistance. This series incorporates a
durable barrier that allows the sensor to operate reliably
in high humidity conditions as well as environments
containing common automotive media. NOTE: Applica-
tions exposing the sensor to media other than what has
been specified could potentially limit the lifetime of the
sensor. Please consult the Motorola factory for more
information regarding media compatibility in your specific
application.
Q. Can I pull a vacuum on P1
A. Motorola pressure sensors are designed to measure
pressure in one direction and are not bi–directional. It is
possible to measure either a positive pressure OR a
negative pressure, but not both. For example, the sensor
can be designed to accept a ”positive” pressure on the
P1 port, providing that P1 is greater or equal to P2 while
staying with in the sensors specified pressure range. Or,
the sensor can measure ”negative” pressure (a vacu-
um)by applying the pressure to the P2 port, again while
P1 is greater or equal to P2 and staying within the
sensors specified range.
Our pressure sensors are based on a silicon diaphragm
and can not tolerate a pressure that alternates from
positive to negative without resulting damage. The
devices are rated for over pressure and burst but should
not be intentionally designed to operate in a bi–direction-
al manner.
If you need to measure both a positive and negative
pressure within the same system, we suggest designing
with two separate sensors, one for each pressure type.
Or, a mechanical pressure transducer should be utilized.
Q. What will happen if I run the pressure sensor beyond
the rated operating pressure
A. For bare elements (uncompensated and compensated
series devices), when you take the sensor higher than
the rated pressure, the part will still provide an output
increasing linearly with pressure. When you go below the
minimum rated pressure, the output of the sensor will
eventually go negative. Motorola, however, does not
guarantee electrical specifications beyond the rated
operating pressure range specified in the data sheet of
each device. The integrated series devices will not
function at all beyond the rated pressure of the part.
These series of parts will saturate at near 4.8 V and 0.2 V
and thus no further change in output will occur.
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Freescale Semiconductor, Inc.
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