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SAE J2735-Draft-Rev28 [issued: 11-10-08]
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98 -
This is an SAE Motor Vehicle Council draft document of the DSRC committee, subject to change.
Used By: This entry is directly used by the following 2 other data structures in this standard (record type,
descriptive name, ASN.1, and XML name (if present) of each):
DF
<XML>, and
DF
In addition, this item may be used by data structures in other ITS standards.
7.3 Data Element: DE_AmbientAirPressure (Barometric Pressure)
Use: This data element is used to relate the measured Ambient Pressure (Barometric Pressure) from a
vehicle or other device. The value of zero shall be used when not equipped. The value of one indicates a
pressure of 580 hPa.
ASN.1 Representation:
AmbientAirPressure ::= INTEGER (0..255)
-- 8 Bits in hPa starting at 580 with a resolution of
-- 2 hPa resulting in a range of 580 to 1,090
XML Representation:
<xs:simpleType name="AmbientAirPressure" >
<xs:annotation>
<xs:documentation>
8 Bits in hPa starting at 580 with a resolution of
2 hPa resulting in a range of 580 to 1, 090
</xs:documentation>
</xs:annotation>
<xs:restriction base="xs:unsignedByte"/>
</xs:simpleType>
Used By: This entry is used directly by one other data structure in this standard, a DF called
DF_VehicleStatus <ASN> <XML>. In addition, this item may be used by data structures in other ITS
standards.
Remarks: Definition: The pressure exerted by the weight of the earth's atmosphere, equal to one bar, 100
kilopascals, or 14.7 psi (often rounded off to 15 psi) at sea level. Barometric pressure changes with the
weather and with altitude. Since it affects the density of the air entering the engine and ultimately the
air/fuel ratio, some computerized emissions control systems use a barometric pressure sensor so that the
spark advance and EGR flow can be regulated to control emissions more precisely.
To convert pounds per square inch to kilopascals, multiply the PSI value by 6.894757293168361.
To convert kilopascals to pounds per square inch, multiply the kpa value by .14503773773020923.
7.4 Data Element: DE_AmbientAirTemperature
Use: This data element is used to relate the measured Ambient Air Temperature from a vehicle or other
device. Its measurement range and precession follows that defined by the relevant ODB-II standards. This
provides for a precision of one degree centigrade and a range of -40 to +150 degrees encoded in a one byte
value. The value of -40 deg C is encoded as zero and every degree above that increments the transmitted
value by one resulting in a transmission range of 0 to 191. Hence, a measurement value representing 25
degrees centigrade is transmitted as 40+25=65 or Hex 0x41.
ASN.1 Representation:
AmbientAirTemperature ::= INTEGER (0..191) -- in deg C with a -40 offset
XML Representation:
<xs:simpleType name="AmbientAirTemperature" >
<xs:annotation>
<xs:documentation>