Vernier Conductivity Probe User Manual

Conductivity
Probe

(Order Code CON-BTA)

The Conductivity Probe can be used to
measure either solution conductivity or
total ion concentration of aqueous samples
being investigated in the field or in the
laboratory. Conductivity is one of the most common environmental tests of aquatic
samples. Even though it does not tell you specific ions that are present, it quickly
determines the total concentration of ions in a sample.

Note: Vernier products are designed for educational use. Our products are not
designed nor are they recommended for any industrial, medical, or commercial
process such as life support, patient diagnosis, control of a manufacturing
process, or industrial testing of any kind.

What's Included

 Conductivity Probe
 90 mL bottle of 1000 µS/cm NaCl standard solution

Compatible Software and Interfaces

See www.vern ier. com/ manu als/con- bt a for a li st o f interfa ces an d so ftware
compatible with the Conductivity Probe.

Getting Started

1. Connect the sensor to the interface (LabQuest Mini, LabQuest 2, etc.).

2. Start the appropriate data-collection software (Logger Pro, Logger Lite,
LabQuest App) if not already running, and choose New from File menu.

The software will identify the sensor and load a default data-collection setup. You
are now ready to collect data.

If you are collecting data using a Chromebook™, mobile device such as iPad

®

or
Android™ tablet, or a Vernier wireless sensor or interface, please see the following
link for up-to-date connection information:

www.vern ier.co m/sta rt/ con -b ta

Using the Product

1. Set the range switch on the sensor.

2. Thoroughly rinse the lower section of the probe using distilled or deionized

water.

3. Connect the sensor following the steps in the Getting Started section of this

user manual.

4. When you are finished making measurements, rinse the electrode with distilled

water. Store d ry.

Videos

View videos related to this product at www.vern ier.co m/con -b ta

Calibration

For many experiments, calibrating the Conductivity Probe is not required. A
calibration equation is stored on each probe before they are shipped, which is used
as a default by Vernier software.

For the most accurate measurements with this sensor, we recommend calibration. It
is a simple process that takes only a few minutes.

 For instructions for Conductivity Probe calibration using Logger Pro computer

soft ware, see

www.vern ier.co m/til/2341

 For instructions for Conductivity Probe calibration using LabQuest App, see

www.vern ier.co m/til/3394

 For instructions for Conductivity Probe calibration using Graphical Analysis

with a Chromebook, see

www.vern ier.co m/til/3631

 For instructions for Conductivity Probe calibration using Graphical Analysis

with an iOS or Android device, see

www.vern ier.co m/til/3630

In order to calibrate a Conductivity Probe, or to confirm that a saved calibration is
accurate, you should have a supply of conductivity standard solutions that cover
the range of the conductivity values you will be measuring. For more information
about conductivity standard solutions, including recipes for preparation, see

www.vern ier.co m/til/760

Specifications

Low range 0 to 200 µS/cm (0 to 100 mg/L TDS)

Mid range 0 to 2000 µS/cm (0 to 1000 mg/L TDS)

High range 0 to 20,000 µS/cm (0 to 10,000 mg/L TDS)

Type ABS body, parallel graphite electrodes

Response time 98% of final reading in 5 seconds

Temperature compensation automatic from 5 to 35°C

Temperature range 0 to 80°C

Accuracy using factory
calibration

±8% of full-scale reading for low range

±3% of full-scale reading for mid range

±4% of full-scale reading for high range

Accuracy using custom
calibration

±2% of full-scale reading for each range

Shaft diameter 12 mm OD

Care and Maintenance

 When you have finished using the Conductivity Probe, simply rinse it off with

distilled water and blot it dry using a paper towel or lab wipe. The probe can

2

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. Imp ortant: Avoid scratching the inside electrode surfaces
of the elongated cell.

 Important: Do not place the electrode in viscous, organic liquids, such as

heavy oils, glycerin (glycerol), or ethylene glycol. Do not place the probe in
acetone or other organic solvents, such as pentane or hexane.

How the Sensor Works

The Vernier Conductivity Probe 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.

The Conductivity Probe is actually measuring conductance, defined as the
reciprocal of resistance. When resistance is measured in ohms, conductance is
measured using the SI unit, siemen s (formerly known as a mho). Since the siemens
is a very large unit, aqueous samples are commonly measured in microsiemens, or
µS.

Even though the Conductivity Probe is measuring conductance, we are often
interested in finding conductivity of a solution. Conductivity, C, is found using
the following formula:

C=G•k

c

where G is the conductance, and kc is the cell constant. The cell constant is
determined for a probe using the following formula:

k

c

=d/A

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

c

=d/A=1.0cm/1.0cm2=1.0cm

-1

The conductivity value is found by multiplying conductance and the cell constant.
Since the Vernier Conductivity Probe also has a cell constant of 1.0 cm

-1

, 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

c

= (1000 µS) X (1.0 cm-1) = 1000 µS/cm

3

A potential difference is applied to the two probe electrodes in the Conductivity
Probe. 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 the Conductivity Probe 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 relatively inert graphite electrodes.

The Vernier Conductivity Probe 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 extends into the space between the graphite
electrodes. Readings are automatically referenced to a conductivity value at 25°C;
therefore, the Conductivity Probe will give the same conductivity reading in a
solution that is at 15°C as it would if the same solution were warmed to 25°C.
This means you can calibrate your probe in the lab, and then use these stored
calibrations to take readings in colder (or warmer) water in a lake or stream. If the
probe was not temperature compensated, you would notice a change in the
conductivity reading as temperature changed, even though the actual ion
concentration did not change.

Troubleshooting

When testing a Conductivity Probe, it is best to measure a standard solution
because it is easier to determine if the sensor is reading correctly. If your
Conductivity Probe is reading differently from the standard solution, you may
simply need to calibrate the sensor. See the Calibration section for more
information. Here are some other tips to ensure best data collection practices:

 Blot the inside and outside of the electrode cell dry to avoid water droplets

diluting or contaminating the sample to be tested.

 Be sure the electrode surfaces in the elongated cell are completely submerged

in the liquid and that there are no bubbles around the electrode surface.

 Gently swirl the probe, or stir the solution with a stirring bar and stir plate,

during data collection.

 Do not completely submerge the sensor. The handle is not waterproof.

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