Care And Maintenance; How The Sensor Works - Vernier Go Direct GDX-CONPT Quick Start Manual

Battery life (single ~24 hours
full charge)
Battery life (long ~500 full charge cycles (several years depending on
term) usage)

Care and Maintenance

When you have finished using Go Direct Platinum-Cell Conductivity, simply
rinse it off with distilled water and blot it dry using a paper towel or lab wipe.
The probe can then be stored dry.
If the probe cell surface is contaminated, soak it in water with a mild detergent
for 15 minutes. Then soak it in a dilute acid solution (0.1 M hydrochloric acid
or 0.5 M acetic acid works well) for another 15 minutes. Then rinse it well with
distilled water. Important: Avoid scratching the inside electrode surfaces of the
elongated cell.
Battery Information
Go Direct Platinum-Cell Conductivity contains a small lithium-ion battery in
the handle. The system is designed to consume very little power and not put
heavy demands on the battery. Although the battery is warranted for one year,
the expected battery life should be several years. Replacement batteries are
available from Vernier (order code: GDX-BAT-300)
Storage and Maintenance
To store Go Direct Platinum-Cell Conductivity for extended periods of time, put
the device in sleep mode by holding the button down for at least three seconds.
The red LED will stop flashing to show that the unit is in sleep mode. Over
several months, the battery will discharge but will not be damaged. After such
storage, charge the device for a few hours, and the unit will be ready to go.
Exposing the battery to temperatures over 35°C (95°F) will reduce its lifespan. If
possible, store the device in an area that is not exposed to temperature extremes.
Water Resistance
Go Direct Platinum-Cell Conductivity is not water resistant and should never be
immersed in water.
If water gets into the device, immediately power the unit down (press and hold
the power button for more than three seconds). Disconnect the sensor and
charging cable, and remove the battery. Allow the device to dry thoroughly
before attempting to use the device again. Do not attempt to dry using an
external heat source.

How the Sensor Works

Go Direct Platinum-Cell Conductivity measures the ability of a solution to
conduct an electric current between two electrodes. In solution, the current
flows by ion transport. Therefore, an increasing concentration of ions in the
solution will result in higher conductivity values.
Go Direct Platinum-Cell Conductivity is actually measuring conductance,
defined as the reciprocal of resistance. When resistance is measured in ohms,
conductance is measured using the SI unit, siemens (formerly known as a mho).
Aqueous samples are commonly measured in microsiemens, µS.
Even though Go Direct Platinum-Cell Conductivity is measuring conductance,
we are often interested in finding conductivity of a solution. Conductivity, C, is
found using the following formula:
where G is the conductance, and k
determined for a probe using the following formula:
where d is the distance between the two electrodes, and A is the area of the
electrode surface.
For example, the cell in Figure 1 has a cell constant:
k = d / A = 1.0 cm / 1.0 cm
c
The conductivity value is found by multiplying conductance and the cell
constant. Since Go Direct Platinum-Cell Conductivity also has a cell constant of
-1
1.0 cm , its conductivity and conductance have the same numerical value. For a
solution with a conductance value of 1000 µS, the conductivity, C, would be:
C = G•k = (1000 µS) × (1.0 cm
c
A potential difference is applied to the two probe electrodes in Go Direct
Platinum-Cell Conductivity. The resulting current is proportional to the
conductivity of the solution. This current is converted into a voltage.
Alternating current is supplied to prevent the complete ion migration to the two
electrodes. Each cycle of the alternating current, the polarity of the electrodes is
reversed, which in turn reverses the direction of ion flow. This very important
feature of Go Direct Platinum-Cell Conductivity prevents most electrolysis and
polarization from occurring at the electrodes. Thus, the solutions that are being
measured for conductivity are not fouled. It also greatly reduces redox products
from forming on the platinum-cell electrodes.
Temperature Compensation
Go Direct Platinum-Cell Conductivity has two temperature compensation
settings: 0% and 2%. The 2% setting is designed for most aqueous salt
solutions.
If you select the 2% setting, the sensor reading is automatically temperature
compensated between temperatures of 5 and 35°C. Note that the temperature of
a solution is being read by a thermistor that is embedded in the electrode.
Readings are automatically referenced to a conductivity value at 25°C;
therefore, Go Direct Platinum-Cell Conductivity gives the same conductivity
reading in a solution that is at 15°C as it would if the same solution were
3
C = G × k
c
is the cell constant. The cell constant is
c
k = d /A
c
2 -1
= 1.0 cm
-1
) = 1000 µS/cm