YOKOGAWA vigilantplant DM8, User Manual

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<2. PRINCIPLES OF OPERATION>
2-3
IM 12T03A01-02E
The amplifier converts the output of the capacitance pickup electrode into an AC voltage
to amplify it. This frequency signal is, together with the temperature signal from the RTD,
transmitted to the converter. A part of the frequency signal is fed back to the piezoelectric element
to maintain the vibrator oscillation.
2.2.2 Density Converter
Figure 2.3 is a block diagram of the density converter.
As shown in the diagram, the density converter receives the density signal (frequency) F and
temperature signal (voltage) RT from the density detector and finally outputs a 4 to 20 mA
analog signal and 0 to 1 V DC signal corresponding to the liquid density converted to that at
reference temperature. The digital signals of densities at measuring temperature and reference
temperature, and measuring temperature and measuring temperature value are also output.
The converter circuit comprises three printed circuit boards. Changing displayed items or setting
constants are performed by keys or transfer switches on the front panel.
CPU EEPROM
PC
PC
PC
PC
PC
0 to 1 V
4 to 20 mA
TD
200 V
Reference frequency
Ref. temp. Zero
Frequency of Density (F)
Temp. Signal
(RT)
R/V
Ref. temp. Span
Multiplexer
Multiplexer V/F
Integrator
V/I
Zero
Span
Driver
Key &
Display
Controller
Key
LED
Digital Output
Fail Alarm
Figure 2.3 Block Diagram of Density Converter
5th Edition : Dec. 11, 2015-00