SMAR DT302, Owner'S Operation And Maintenance Manual

Page: 32 / 84

DT302 – Operation, Maintenance and Instructions Manual
2.2
Functional Description – Electronics
Refer to the block diagram. The function of each block is described below.
PROBE SENSOR ASSEMBLY
MAIN CIRCUIT BOARD
LOCAL ADJUSTE
CPU
EEPROM
DISPLAY
CONTROLLER
FIRMWARE
DOWNLOAD
INTERFACE
EEPROM
FLASH
RAM
MODEM
DISPLAY BOARD
SUPPLY
SIGNAL
SHAPING
POWER
SUPPLY
POWER
ISOLATION
SUPPLY
SIGNAL
ISOLATION
EEPROM
OSCILATOR
C
I
C
II
PRESSURE
REPEATERS
TEMPERATURE
Figure 2.2 - DT302 Block Diagram Hardware
Probe
Part of the transmitter directly in contact with the process.
Pressure Repeaters
It transfers to the capacitive sensor the differential pressure detected in the process.
Temperature Sensor
It captures the process fluid temperature.
Oscillator
This oscillator generates a frequency as a function of sensor capacitance.
Signal Isolator
The control signals from the CPU and the signal from the oscillator are isolated to avoid ground
loops.
Central Processing Unit (CPU), RAM, FLASH and EEPROM
The CPU is the intelligent portion of the transmitter, being responsible for the management and
operation of measurement, block execution, self-diagnostics and communication. The program is
stored in a FLASH memory for easy upgrade and saving data on power-down event occurrence. For
temporary storage of data there is a RAM. The data in the RAM is lost if the power is switched off,
however the main board has a nonvolatile EEPROM memory where the static data configured that
must be retained is stored. Examples of such data are the following: calibration, links and
identification data.
Sensor EEPROM
Another EEPROM is located within the sensor assembly. It contains data pertaining to the sensor's
characteristics at different pressures and temperatures. This characterization is done for each
sensor at the factory. It also contains the factory settings; they are useful in case of main board
replacement, when it does an automatic upload of data from the sensor board to main board.