Specifications

Units of Measurement
The basic unit of conductivity is the Siemens (S), formerly called the
mho. Since cell geometry aects conductivity values, standardized
measurements are expressed in specic conductivity units (S/cm) to
compensate for variations in electrode dimensions. Specic conductivity
(C) is simply the product of measured conductivity (G) and the electrode
cell constant (L/A), where L is the length of the column of liquid between
the electrode and A is the area of the electrodes.
C = G x (L/A)
If the cell constant is 1 cm
-1
, the specic conductivity is the same as
the measured conductivity of the solution. Although electrode shapes
vary, an electrode can always be represented by an equivalent
theoretical cell.
Conductivity Temperature Compensation
Conductivity measurements are temperature dependent. The degree to
which temperature aects conductivity varies from solution to solution
and can be calculated using the following formula:
Gt = Gt
std
{1 + α(T-T
std
)}
where:
Gt = Conductivity at measured Temperature T in °C;
Gt
std
= Conductivity at Reference (Normalisation) Temperature T
std
in °C;
α = Temperature Coecient of solution at T
std
in °C;
T
std
= Reference or Normalisation Temperature in °C
All meters have either fixed or adjustable automatic temperature
compensation referenced to a standard temperature – usually 25 °C.
Most meters with xed temperature compensation use α of 2 % per °C
(the approximate α of NaCl solutions at 25 °C). Meters with adjustable
temperature compensation let you to adjust the α to more closely match
the α of your measured solution.
Conductivity Meter Calibration and Cell Maintenance
Conductivity meters and cells should be calibrated to a standard solution
before using. When selecting a standard, choose one that has the
approximate conductivity of the solution to be measured.
A polarized or fouled electrode must be cleaned to renew the active
surface of the cell. In most situations, hot water with a mild liquid
detergent is an eective cleanser. Acetone easily cleans most organic
matter, and chlorine solutions will remove algae, bacteria or molds. To
prevent cell damage, abrasives or sharp objects should not be used to
clean an electrode. A cotton bud works well for cleaning but care must
be taken not to widen the distance of cell.
Conductivity Cells
Most conductivity meters have a 2-cell electrode available in either dip or
ow-through styles. The electrode surface is usually platinum, titanium,
gold-plated nickel, or graphite. The 4-cell electrode uses a reference
voltage to compensate for any polarization or fouling of the electrode
plates. The reference voltage ensures that measurements indicate actual
conductivity independent of electrode condition, resulting in higher
accuracy for measuring pure water.
The Eutech EC620165 4-cell conductivity electrode (cell constant
K=1.0) with in-built ATC and DIN connector is available for use
with the bench meters CON 1500, PC 6000, PC 6500 and PCD 6500.
ECCONSEN9203J 4-cell conductivity electrode with ATC and 3 m
cable is available for COND 600, COND 610, PCD 650 and CD 650
handheld meters.
Important Features to Consider in a Conductivity Meter
• Auto-Ranging
Meter automatically selects the appropriate range for measurement.
There is no need to change the dial, multiply values on the display, or
turn the potentiometer.
•
Temperature Compensation
A cell with built-in temperature sensor allows the meter to make
adjustments to the conductivity or TDS readings based on changes in
solution temperature.
•
TDS Conversion Factor
When a solution does not have a similar ionic content to natural water
or salt water, then a TDS conversion factor is needed to automatically
adjust the readings.
•
Adjustable Temperature Coecients
The TDS of certain samples, such as alcohols and pure water, are aected
by changes in temperature. An adjustable temperature coecient
allows the user to compensate for temperature changes on the solution
being measured.
•
Adjustable Cell Constant
Adjusts the reading on the display to reect use of a cell with a constant
other than k=1.0 cm
-1
.
Eutech’s wide range of conductivity meters incorporates these
features for consistent, accurate and reliable measurements.
Conductivity/TDS | About Conductivity/TDS Measurement
page | 31
Figure 1
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