YOKOGAWA vigilantplant DM8, User Manual

Page: 51 / 63

<4. OPERATION>
4-10
IM 12T03A01-02E
4.4 Calibration
The vibration type density meter should be calibrated as occasion demands to keep the specified
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 accurate measurement. On
the other hand, in calibration with standard solution, the solution density is once determined at
the fixed value, density measurement of sample liquid should not be repeated at a laboratory.
The one-point calibration is equal to that omitting the 2nd calibration two-point calibration, so, the
two-point calibration using standard solution and sample liquid is described as follows. Since the
following is described assuming that the density converter is installed in the vicinity of the density
detector, for the connector installed away from the detector, please edit the manual for it and
carry out the calibration according to the manual.
4.4.1 Calibration with Standard Solution
Provide two kinds of standard solution whose density at reference temperatures is already known
*1. One density (standard solution 1) should be near to the low limit of the measuring range and
the other to the high limit (standard solution 2). Temperature coefficients (g/cm 3 /°C) of these
standard solutions should be obtained beforehand.
*1: When measuring the density of the standard solution, use a hydrometer whose minimum scale is 0.0005 kg/cm 3 .
Calibration should be made in the following procedure. During calibration, only the density
detector and the density converter are to be driven and the unit to receive output signals from the
converter can remain stopped.
(1) Set the converter to “CAL” mode and input data corresponding to function No. ‘3’, ‘4’, ‘5’, ‘7’,
‘8’ and ‘9’. For pressure compensation, subtract the compensation value obtained in Section
4.3.6 from density of standard solution, and set them to function No. ‘3’ and ‘7’.
(Note) When the compensation value is a minus number, the set value becomes large than the standard solution density.
(2) Purge the inside of the vibrator with air as follows. Fully close the ball valve “BV1” and the
needle valve “NV4” in the sampling unit. Fully open the needle valve “NV2” and “NV3”,
connect an air pipe to the outlet port of the needle valve “NV3” and blow air for one or two
minutes. Pneumatic pressure should be 0.2 to 0.3 MPa*1.
*1: For sample liquid remains in the vibrator, blow it out by 0.05 MPa G pneumatic pressure, and increase the pressure up to 0.2 to
0.3 MPa to dry the inside of the vibrator.
(3) Pouring 18 to 20 mL of standard solution 1 into the vibrator, avoiding air bubble entering it is
described here.
Firstly, remove the blind plugs from the pouring ports for the standard solution (two places)
located on the detector base plate. Secondly, pour the standard solution into the pouring
port using the injector (accessory) so that the solution flows along the inner wall of the
vibrator tube. Using the pouring port near to the sample inlet is recommended. If the injector
is stained, clean it with alcohol.
(4) Read the measured density value at the reference temperature. It is displayed with the
mode selector switch 3 set to “DSPL” and function No. not displayed.
(5) Since calibration with standard solution 1 is made two times, blow out the used standard
solution from the vibrator. Before blowing, plug the pouring orts (two places), and blow air
according to (2).
(6) Carry out the operations of (3) and (4) to confirm that the same results as that of (4) is
achieved.
(Note): If the result differs from (4), repeat the operations of (3) and (4).
(7) For the calibration 1 computation, press “SET” key at the function No. ‘6’. ‘CAL-1’ flashes
during computation and the density at the reference temperature is displayed after the
computation finishes (NOTE (a) ). Check that this value is the correct density (NOTE (b) ) of
the standard solution 1.
5th Edition : Dec. 11, 2015-00