SMAR ld301, Инструкция по эксплуатации и техническому обслуживанию

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LD301- manual de Instruções, Operação e manutenção
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 intelligent portion of the transmitter, being responsible for the management and
operation of all other blocks, linearization and communication.
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 14-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.
Modem
This system providers the data exchange between the se serve-master digital communication
. The transmitter demodulates information from the current line, then modulates the relies
sending then over the line. A "1" is represented by 1200 Hz and "0" by 2200 Hz. The frequency
signal is symmetrical and does not affect the DC-level of the 4-20 mA signal.
Power Supply
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.
The ld301, in the transmitter mode, shows failure indication at 3.6 mA if configured for low
signal failure; at 21 mA, if configured for high signal failure; 3.8 mA in the case of low saturation;
20.5 mA in the case of high saturation and measurements proportional to the applied pressure
in the range between 3.8 mA and 20,5 mA. 4 mA corresponds to 0% of the working range and
20 mA to100 % of the working range.
Fig. 2.2 – LD301 Block Diagram Hardware