SMAR LD290, Operation And Maintance Manual

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LD290- Operation and Maintenance Instruction Manual
2.2
Functional Description - Hardware
Refer to the block diagram Figure 2.2. The function of each block is described below.
Oscillator
This oscillator generates a frequency as a function of sensor capacitance.
Signal Isolator
The Control signals from the CPU are transferred through optical couplers, and the signal from
the oscillator is transferred through a transformer.
(CPU) Central Processing Unit and PROM
The CPU is the portion of the transmitter, being responsible for the management and operation
of all other blocks..
The program is stored in an external PROM. For temporary storage of data the CPU has an
internal RAM. The data in the RAM is lost, if the power is switched off, however the CPU also
has an internal nonvolatile EEPROM where data that must be retained is stored. Examples of
such data are: calibration, configuration and identification data.
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.
D/A Converter
Converts the digital data from the CPU to an analog signal with 15-bits resolution.
Output
Controls the current in the line feeding the transmitters.
It acts as a variable resistive load whose value depends on the voltage from the D/A converter.
Power Supply
P
H
P
L
PRESSURE
SENSOR
ELECTRONIC
CONVERTER
CONVERTER
TEMPERATURE
DIGITAL
DISPLAY
4-20 mA
PROCESSING UNIT
RANGES
SPECIAL FUNCTIONS
OUTPUT CONTROL
D/A
CONVERTER
MATH
COPROCESSOR
DISPLAY
CONTROLLER
LOCAL ADJUSTMENTS
ZERO / SPAN
HT3012
POWER
SUPPLY
SENSOR
MAIN BOARD
OUTPUT
ELECTRONIC
CONVERTER
Figure 2.2
– LD290 Block Diagram Hardware
Power shall be supplied to the transmitter circuit using the signal line (2-wire system). The
transmitter quiescent consumption is 3.6 mA; during operation, consumption may be as high as
21 mA, depending on the measurement and sensor status.
Power Supply Isolation
The sensor power supply is isolated from the main circuit by this module.
Display Controller
It receives the data from the CPU and actives the LCD segments. Also it actives the back plane
and the control signals for each segment.
Local Adjustment
Two switches that are magnetically activated. The magnetic tool without mechanical or electrical contact
can activate them.