Sartorius IB 31000 P Specifications download pdf (Page 18)

6.2 Instructions for use

When the gauge has been kept dry for a long period, it should be cleaned and the electrodes should

be placed under water for a few hours before starting the actual measurement. At the beginning of

each experiment it is recommended to clean the rods and the reference-electrode of the gauge with

a piece of cloth soaked in a three percent solution of nitric acid (HN0

or "degreaser", the latter is

generally used in the Hydromechanics Laboratory .

Furthermore it is recommended to allow the instrument a warm-up period of at least half an hour.

After the electronics have warmed up the instrument must be calibrated. For that purpose the probe

is attached to a point-gauge, for instance. The depth ofthe probe is chosen in such a way, that during

the calibration and the actual measurement the top of the reference electrode is immersed for at least

4 cm. A recommended immersion-depth is half the value of the selected range plus 4 cm, measured

from the top of the reference electrode in the stagnant fluid. Then the pointer of the indicating meter

on the front panel of the main amplifier and also the output voltage must be adjusted to its centre-

scale position which corresponds with

0.0

Vdc output. After these preparations the calibration of the

instrument can be carried out, i.e. changing the immersion-depth of the probe by means of the point-

gauge and measuring the change in the output voltage.

is recommended to determine at least five

calibration points and calculate the best straight line through these points with a least squares

approximation.

When several wave height meters are used simultaneously and close to each other, they might

influence each other. However, for distances larger than

cm, this influence is negligible.

6.3

The influence of clay and salt on the Iinearity

The described wave height meters are not designed for employment in saline water. As a result of

that some doubts arose about the linearity of the device in saline water and a suspension of China

Clay. Therefore some experiments were carried out to measure the linearity under these conditions.

In these experiments only the devices built between 1974 and 1978 were tested. A description of these

tests and the results will be given next.

A large tank was filled with a fluid. A probe attached to a point-gauge is immersed in the fluid. The

output voltage

(V)

is measured with a voltmeter. The change in water depth in the tank due to a

change of the immersed depth

(11)

of the probe is negligible. In this configuration five-point

calibrations were carried out for three ranges, namely 5, 10 and 20 cm and several fluids, including

tap-water, saline tap-water and saline tap-water with China Clay.

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Sartorius IB 31000 P Specifications Page 18