Yokogawa DM8C/VD6 Liquid Density Analyzer - Manual (Page 51)

< 4. OPERATION >
4-9
IM 12T03A01-02E
4.3.6 Pressure Compensation
Pressure compensation means to compensate the shift generated by measurement under
operating pressure. The compensation should be carried out as necessary only for calibration under
atmospheric pressure.
Measured value is affected up to +0.00005 g/cm 3 by 100 kPa pressure variance.
Therefore, for liquid under pressure approximating to the atmospheric pressure calibrated value under
atmospheric pressure can be used. Pressure compensation is to be carried out to minimize effects
generated by high operating pressure.
Compensation data is obtained by conducting sample liquid. Measure the data according to the
following procedure when the liquid density is stable. The procedure assumes that sample liquid is
already conducted according to Section 4.3.3.
(1) Fully open the needle valve “NV4” and read P from the pressure gauge. At the same time, obtain
density at the reference temperature indicated on the density converter.
(2) Fully close the ball valve “BV1”, and open the needle valve “NV3” to equalize the sample
liquid pressure in the detector to the atmospheric pressure. Obtain density at the reference
temperature indicated on the density converter.
(3) Calculate the compensation data using the densities obtained in (1) and (2).
Compensation data (g/cm 3 ) =
Density under working pressure – density under atmospheric pressure
When calibration the compensation data should be subtracted from the density value of the
standard solution.
STEAM IN
CONDENSATE OUT
V2
a
a
V1
b
ST1
a'
a'
b'
TI
F
FM
NV1
PI
NV2
DD
NV3
NV4 BV1
Element specifications
F: Strainer body; SUS316
Element; SUS316, or Ni (option)
PI: Pressure gauge, 0 to 1MPa or 0 to 2MPa, SUS316
TI: Thermometer. 0 to 100 °C or 0 to 150 °C, SUS316
FM: Flowmeter, tapered metal tube flowmeter, 1 to 10 l/min, SUS316
BV1: Ball valve, SUS316
NV1 to 4: Needle valve, SUS316
DD: Density
detector
V1, V2: Valve
ST1: Steam trap
SAMPLE IN
SAMPLE OUT
Figure 4.5 Flow Diagram
4.4 Calibration
The vibration type density meter should be calibrated as occasion demands to keep the specifi ed
accuracy.
Calibration has two methods: one-point calibration and two-point calibration, and each method is
carried out by either sample liquid or standard solution. The calibration with sample liquid is not
requiring stopping operation and pressure compensation resulting in assurate measurement. On the
other hand, in calibration with standard solution, the solution density is once determined at the fi xed
value, density measurement of sample liquid should not be repeated at a laboratory.