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HPB\HPA User Manual
4 FUNCTIONAL OPERATION
4.1 OVERVIEW
The 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
which, when modeled over a matrix of pressures and temperatures at the factory, provides a digitally
compensated pressure reading. The HPB has an accuracy of 0.03% of full scale (FS) over a -40 to +85°C
temperature range. This accuracy is achieved by compensation algorithms in the microprocessor. Because
of the internal digital circuitry,
via RS-485 signals or RS-
connected to a computer, the user can modify the pressure reading rate, integration times, units of pressure,
thresholds for deadbands and more.
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. Any configuration parameter that can be
changed by a command may be retrieved by use of that same command except baud rate or parity.
Commands used to change parameters must be preceded by an enabling command (WE or NE), 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.
4.2 WHAT IS INTEGRATION?
The input pressure is converted to an analog electrical signal at the pressure sensor. This signal feeds into a
delta-sigma analog-to-digital (A/D) converter where it is changed into a digital signal representing the
pressure value. During the A/D conversion cycle, the signal is integrated over time. That is, the pressure
reading is averaged (integrated) over the A/D conversion cycle so the resultant digital value is the summation
of the average pressures observed during the cycle. This conversion cycle is controlled by the user with the
Deadband and Sensitivity (DS), Synchronization Integration (SI), Idle Count (IC), and Integration (I=)
commands.
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having a digital output capability is straight forward. The digital readings are transmitted
232 signals, which are commonly available on most personal computers. When
Figure 4.1—HPB Block Diagram
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