Sartorius IB 31000 P Specifications download pdf (Page 23)

Using the experimental data the wave number k = 211"L -t can be estimated and the pressure

amplitude

can then be calculated.

From the results presented in table 7.3.2 the conclusion can be drawn that the experimental results

correspond very well with what may be expected according to linear short-wave theory and

consequently that the Oruck POCR-8I pressure transducers perform very well.

Conductivity probe

8.1 Description

The electrical conductivity is the reciprocal of resistivity. According to Weast [4] this quantity is

defined by:

R = r

(8.1.1)

where R is the resistance of a uniform conductor, I is its length in the direction of the current, A is

its cross sectional area and ris its resistivity. The resistivity is usually expressed in Ohm-centimetres

[O·cm]. Consequently the conductivity is expressed in Q-t'cm't, which corresponds with Siemens per

cm [S'cm"],

The conductivity of c1earwater is primarily determined by the presence of lens, the conductivity of

distilled water, for instance, is very low because ofthe absence of ions. An other important parameter

is the temperature. When the temperature changes the mobility of ions will change resulting in a

change in conductivity.

The conductivity of water with a constant composition of ions decreases if a certain amount of

sediment is added. The principle of a conductivity concentration meter is based on this phenomenon.

At Delft Hydraulics such a concentration meter was developed and it consists of a probe and a signal

processor. The probe is composed of four separate electrodes and is supplied with an alternating

current in order to eliminate polarisation effects.

is shaped in a wedge form with a measuring

volume of about 3

mm'.

The operation range of sediment concentrations within which this device can

operate accurately is from about 250 to 1300 kg-m". lts accuracy is estimated at about 10% of the

local concentration [3].

8.2 Instructions for use

The conductivity meter supplied by Delft Hydraulics is designed to measure concentrations of

sediment in fresh water. However, in the experiments of De Wit [5] salt water was used with a

salinity of

50/00.

As a consequence, the conductivity meter present in the Hydromechanics Laboratory

was adjusted to operate properly in this environment.

The conductivity concentration meter has to be calibrated before or after every measurement, for the

conductivity change of the pore water caused by a concentration change depends on the type of

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Sartorius IB 31000 P Specifications Page 23