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4.0 FUNCTIONAL OPERATION
4.1 Overview
Honeywells Precision Pressure Barometer (HPB) is based on a silicon piezoresistive sensor coupled with a
microprocessor and other electronic circuitry. The Piezoresistive sensor contains both pressure sensitive and
temperature sensitive elements. After testing the sensor over a matrix of pressure and temperatures at the factory,
values are stored in the EEPROM and used by the microprocessor to correct for any sensor non-linearities. Because
of the internal digital circuitry, having a digital output capability is straight forward. The digital readings are
transmitted via TTL-level signals in either a ring or multi-drop configuration. When connected to a computer via an
RS232-to-TTL converter, the user can modify the pressure reading rate, integration times, units of pressure,
thresholds for deadbands, etc.
Figure 1. HPB Block Diagram
The HPB can be tailored to specific application requirements. Configuration information is sent to, or read from,
the HPB by user command messages over the serial port. Most configuration parameters that can be changed by a
command may be retrieved by use of that same command. Commands used to change parameters must be preceded
by an enabling command (
WE
), but commands used to retrieve information do not require an enable. All
configuration changes are stored in the HPB RAM for immediate use until power is removed. These configuration
changes are only made permanent in the EEPROM when the user executes the Write Enable (
WE
) command
followed by the EEPROM Store Parameters (
SP
) command. (Exceptions to this are the
A=
,
B=
,
C=
, and
D=
commands, which are immediately stored to EEPROM if preceded by the
WE
command.)
The HPB is a low power device. It can be configured to enter a micro-power shut down mode by either sending a
simple command (
See OP=O Command
) or by ap5V to the power control pin on the electrical connector.
If the micro-power mode was entered with a simple command, normal operation is restored by momentarily
grounding the power control pin. If the HPB was configured to enter a micro-power state by ap5V to the
power control pin (
See OP=P Command
), normal operation is restored by permanently grounding the power control
pin.
Voltage Regulator
COM
(Digital
Serial
Data)
DC
Power
Pressure
Input
HPB
Pressure
Sensor
Temperature
Sensor
16 bit
Analog
to
Digital
Converter
Micro-
processor
RAM
Power
Control
TTL-Level
EEPROM