Azbil ALTJ 9000 Series, User Manual, Page: 17 / 68

2-3
Chapter 2 Function and Configuration
„
Operating Principle
The pressure-receiving section transmits the water pressure through the metallic dia-
phragm and sealed liquid to the sensor section. In the sensor section, the sensor deforms
to a degree that corresponds to the transmitted pressure, and the resistance value changes.
A Wheatstone bridge circuit detects the resistance and sends it to the transmission section
after A-D conversion. At the same time, the auxiliary sensor (temperature sensor), which is
built onto the sensor chip, detects the ambient temperature and sends it to the transmission
section. The digitalized signal that has been sent to the transmission section is processed
by a microprocessor to convert it into a 4–20 mA DC analog signal proportional to the set
range using D-A conversion. After that, the converted signal is output. All of the pressure
and temperature data for the probe is obtained during manufacturing. In order to do the
calculations necessary to correct the measured pressure to the true pressure, this data is
stored in EEPROM. The microprocessor uses the information in EEPROM and outputs the
result.
Differential pressure
(pressure sensor)
Temperature
sensor
Transmission section
Compound semiconductor sensor
Pressure-
receiving section
A/D
EEPROM
D/A
Static pressure
sensor
Micro-
processor
Lig
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tor
Fig. 2-3. Overall configuration diagram
Hollow cable
Probe Junction box
Power
Analog output
4 to 20 mA DC
during communication
Digital signal
Power supply -
Hollow pipe Hole open to air