salino meter
DESCRIPTION
salinometer pptTRANSCRIPT
Water purity
• Water purity may refer to the absence of
dissolved salts, a measurement in terms of
acidity or alkalinity, or the presence of oil in a
sample.
• Various instruments which make these
measurements, their operating principles and
the need for the measurement, will now be
described.
Water purity
• Water purity, in terms of the absence of salts,
is a necessary requirement where it is to be
used as boiler feed.
• Pure water has a high resistance to the flow
of electricity, i.e. a low conductivity, so much
so that it is considered non-conductive.
Water purity
• . Water containing dissolved salts, in particular sea
water, has a high conductivity.
• A measurement of conductivity is a measure of
purity.
• A pair of electrodes of known area are placed in
the sample solution at a known distance apart.
• The resistance between them is measured and
expressed in conductivity units which are siemens.
Siemens/cell constant
• . A siemen is a reciprocal ohm and represents the
passage of one ampere at one volt potential
through one cubic centimeter of the liquid.
• Where electrodes are smaller than one square
centimeter and spaced closer or farther than one
centimeter then a cell constant is used to correct
the readings obtained.
Salinometer
• . One common type of salinity indicator uses a small
cell containing two platinum electrodes.
• The liquid sample passes through the cell and the
current flow as a result of any conductance is
measured.
• The reading given assumes all conductivity is due to
sodium chloride which, although not strictly accurate,
is acceptable for most practical purposes.
Salinometer
• Electrical conductivity rises with
temperature and thus a temperature
compensating resistor is incorporated in
the measuring circuit.
Salinometer
• In the dionic water purity meter Conductivity is
measured between two platinum wire ring
electrodes and two gunmetal ring electrodes
• . The liquid flows through these rings which are
separated by insulated lengths of tubing, see
Figure .
• In effect measurements are made on two
columns
Salinometer
• . In effect measurements are made on
two columns of liquid.
• A bimetallic strip operates a plunger
which insulates the two columns and
provides temperature compensation to
20°C.
Salinometer
• . Specific conductivity in siemens/cm3 is the
conductance across a centimeter long column
of mercury whose cross-sectional area is one
square Centimeter.
• A much smaller unit, the microsiemen/cm3,
when corrected to 20°C, is known as a dionic
unit..
Salinometer
• Pure distilled water has a Conductance of
about 1 dionic unit while fresh water is about
500 dionic units.
• A de-grassfire should be fitted upstream of
this unit to remove dissolved carbon dioxide
since this will cause errors in measurement
Acidity/alkalinity/p h meter
• Water, when acidic or alkaline, can cause corrosion.
Boiler feed water when acidic or strongly alkaline will
cause corrosion.
• It is usual to monitor and maintain boiler feed water
slightly alkaline. A scale of measurement using pH values
indicates the degree of acidity or alkalinity within a
solution. A solution which is neutral is neither acidic nor
alkaline. The pH scale is a measure of the concentration
of hydrogen ions in a solution using numbers from 1 to 14