Conductivity Probe
The Vernier
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. It can be connected to any
of the Vernier interfaces (ULI, Serial Box Interface, MPLi, or Voltage Input
Unit)t as well as the Texas Instruments CBL System. Conductivity is one of the
easiest environmental tests of aquatic samples. Even though it does not tell
you specific ions that are present, it does quickly determine the total
concentration of ions in a sample. It can be used to perform a wide variety of
tests or planned experiments to determine the changes in or levels of total
dissolved ions or salinity:
Figure 1. Schematic
diagram of the conductivity probe.
• Allow students to
qualitatively see the difference between the ionic and molecular nature of
substance in aqueous solutions This can include differences in strength of
weak acids and basest or the number of
ions that an ionic substance dissociates into per formula unit.
• Use the probe to
confirm the direct relationship between conductivity and ion concentration in
an aqueous solution. Concentrations of
unknown samples can then be determined.
• Measure changes in
conductivity resulting from photosynthesis in aquatic plants, with the
resulting increase in bicarbonate-ion concentration from carbon dioxide.
• Use this sensor for
an accurate on-site measurement of total dissolved solids (TDS) in a stream or
lake survey. Monitor the rate of
reaction in a chemical reaction in which dissolved ions and solution
conductivity varies with time due to an ionic specie being consumed or
produced.
• Perform a
conductivity titration to determine when stoichiometric quantities of two
substances have been combined.
• Use the
Conductivity Probe to determine the rate at which an ionic species diffuses
through a membrane such as dialysis tubing.
• Monitor changes in
conductivity or total dissolved solids in an aquarium containing aquatic plants
and animals. These changes could be due to photosynthesis or respiration.
How the Conductivity Probe Works
The Vernier
Conductivity Probe measures the ability of a solution to conduct an electric
current between two electrodes. In solution, the currant 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,
siemens (formerly known as a mho). Since the siemens is a very large unit,
aqueous samples are commonly measured in microsiemens, or mS.
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 =
Gkc
where G is the
conductance, and kc is the cell constant. The cell constant is
determined for a probe using the following formula:
kc=d/A
where d is the
distance between the two electrodes, and A is the area of the electrode
surface.
1 cm
1
cm
~
d=1cm
Figure 2. Schematic diagram of conductivity probe.
For example, the cell
in Figure 2 has a cell constant: kc = d /A = 1.0 cm / 1.0 cm2
= 1.0 cm-l. 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 mS, the conductivity,
C, would be:
C = Gkc = ( 1000 mS) x ( 1.0 cm-1) = 1000 mS/cm
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 to be read by a Vernier interface or the
CBL System.
Alternating current
is supplied to prevent the complete ion migration to the two electrodes. As
shown in the figure below, with 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.
One of the most
common uses of the Conductivity Probe is to find the concentration of total
dissolved solids, or TDS, in a sample of water. This can be accomplished
because there is generally a direct relationship between conductivity and the
conductivity concentration of ions in a solution, as shown here. The relationship persists until very large
ion concentrations are reached.
Specific
conductivity
(mS/cm)
Ion
Concentration TDS (mg/L)
The Vernier
Conductivity Probe has three sensitivity range settings:
• 0 to 200 mS (0 to 100 mg/L TDS)
• 0 to 2000 mS (0 to 1000 mg/L
TDS)
• 0 to 20,000 mS (0 to 10,000 mg/L
TDS)
These ranges are
selected using a toggle switch on the end of the amplification box attached to
the probe. It is very important to consider this setting when loading or
performing a calibration; no single calibration can be used for all three
settings.
Inventory of Items Included with the Conductivity Probe
Check to be sure that
each of these items was included in your Conductivity Probe container:
• Conductivity Probe
(conductivity electrode with amplifier box)
• Sodium Chloride
Calibration Standard (equivalent to 1000 ,mS/cm, 491 mg/L as NaCl, or 500 mg/L TDS)
• MSDS sheet for
Sodium Chloride Standard Solution
• Conductivity Probe
booklet
Preparing the Conductivity Probe for Use:
You can be ready to
measure conductivity or concentration using the Vernier Conductivity Probe in
just a few minutes:
• To help ensure that
the electrode surfaces are free of residues, soak the lower portion of the probe in distilled water for about 10
minutes. Blot the electrode surfaces dry (on the inside of the elongated hole near the probe tip).
• Connect the
Conductivity Probe to one of the ports(channels) of your Vernier interface box
or TI CBL System. You are now ready to
perform or load a calibration for the probe.
Calibration
The Conductivity
Probe can be easily calibrated at two known levels, using any of the Vernier
data-collection programs. The calibration units can be, mS, mg/L as TDS, mg/L
as NaCl, or any other unit you choose.
• Select the
conductivity range setting on the probe box: low = 0 to 200 mS, medium = 0 to 2000, mS, and high - 0 to 20,000, mS. Note: if you are not sure of which setting to use, you
may first want to load a stored Vernier
calibration for one or more of the settings to determine an approximate value for the solution to be
sampled.
• Zero Calibration
Point: Simply perform this calibration point with the probe out of any
liquid or solution (e.g., in the air).
A very small voltage reading will be displayed on the computer or CBL screen. Call this value 0 mS or 0 mg/L.
• Standard Solution
Calibration Point: Place the Conductivity Probe into a standard solution (solution of known concentration), such as
the sodium chloride standard that is supplied with your probe. Be sure the entire elongated hole with the electrode
surfaces is submerged in the solution. Wait for the displayed voltage to
stabilize. Enter the value of the standard solution (e.g., 1000 mS, 491 mg/L as NaCl,
or 500 mg/L as TDS). For further information on preparing and interpreting
standard solutions, see subsequent sections on calibration.
This method of
calibrating is easy enough that we recommend that you perform a calibration
whenever you use the probe. As an alternative, you can save a calibration
performed using a conductivity range setting (range setting or standard value
in the calibration name), and reload it at a later date.
For even better
results, the two-point calibration can be performed using two standard
solutions that bracket the expected range of conductivity or concentration
values you will be testing. For examples if you expect to measure conductivity
in the range of 600 mg/L to 1000 mg/L (TDS), you may want to use a standard
solution that is 500 mg/L for one calibration point and another standard that
is 1000 mg/L for the second calibration point.
Taking Measurements using the Conductivity Probe
Once the Conductivity
Probe has been calibrated, you are ready to take readings
• Rinse the tip of
the Conductivity Probe with distilled water. Optional: Blot the inside of the
electrode cell dry only if you are concerned about water droplets diluting or
contaminating the sample to be tested.
• Insert the tip of
the probe into the sample to be tested. Important: Be sure the electrode
surfaces in the elongated cell are completely submerged in the liquid.
• While gently
swirling the probe, wait for the reading on your computer, CBL, or calculator
screen to stabilize. This should take no more than 5 to 10 seconds.
• Rinse the end of
the probe with distilled water before taking another measurement.
• If you are taking
readings at temperatures below 15°C or above 30°C, allow more time for the temperature compensation to adjust and
provide a stable conductivity reading.
• 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 non-polar
solvents such as pentane or hexane.
Storage and Maintenance of the Conductivity Probe
• 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 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.
Maintaining and Replacing the Sodium Chloride Standard
Calibration Solution
Having accurate
standard solutions is essential for performing good calibrations. The Sodium
Chloride Calibration Solution that was included with your probe can last you a
long time if you take care not to contaminate it with a wet or dirty probe. You
should perform and save a calibration with your probe while it is new and
uncontaminated. At some point, you will need to resupply yourself with several
standard solutions. To prepare your own standard solutions using solid NaCl or
KCl:
• Use a container
with accurate volume markings (e.g., volumetric flask) and add the amount of
solid shown in the first column of Table 1. This standard can be used to
calibrate using the amount shown in mg/L as NaCl (first column), mg/L as TDS
(second column), or mS/cm (third column).
Table 1.
Standards for the calibration of the conductivity probe.
|
NaCl to make |
TDS and
Conductivity values the NaCl concentration in |
equivalent to first column: |
|
|
total dissolved
solids (TDS) |
conductivity
(microsiemens/cm) |
|
0.0474g (47.4mg/L) |
50 mg/L as TDS |
100 mS/cm |
|
|
500 mg/L as TDS |
1000 mS/cm |
|
|
1000 mg/L as TDS |
2000 mS/cm |
|
|
5000 mg/L as TDS |
10,000 mS/cm |
• Note also that
standard solutions of lower concentration can be prepared by diluting standard
solutions of higher concentration. For example, if you have a solution that is
1000 mg/L, and want to dilute it to obtain a solution that is 200 mg/L, simply take
100 ml of the 1000 mg/L solution and add enough distilled water to it to yield
500 ml of solution (~400 ml of water is added). The new solution has a
concentration of: 1000 mg/L x ( 100 ml/ 500 ml) = 200 mg/L.
• Flinn Scientific
(P.O. Box 21, Batavia, IL 60510, Tel: 800-452-1261) sells a set of four
standard solutions, 5()0-ml bottle of each. The concentrations correspond to
the four solutions shown in Table 1. Here is the ordering information:
- Conductivity Calibration Kit with four
500-ml bottles ...AP 9111.....$19.95
(50 mg/L, 500 mg/L, 1000 mg/L, and 5000
mg/L TDS)
Automatic Temperature Compensation
Your Vernier
Conductivity Probe is automatically temperature compensated between
temperatures of 5 and 35°C. 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.
Specifications
Range of Conductivity
Probe:
• Low flange: 0 to
200 , mS/cm
(0 to 100 mg/L TDS or 0 to 1.63 x 10-3 mol/L as NaCl)
• Mid Range: 0 to
2000 mS/cm
(0 to 1000 mg/L TDS or 0 to 0.017 mol/L as NaCl)
• High Range: 0 to
20,000 mS/cm
(0 to 10,000 mg/L TDS or 0 to 0.19 mol/L as NaCl)
Resolution (with
12-bit interface[1]):
• Low Range: 0.082 mS/cm, 0.041 mg/L TDS
• Mid Range: 0.82 mS/cm, 0.41 mg/L TDS
• High Range: 8.2 mS/cm, 4.1 mg/L TDS
Accuracy: ±l% of full-scale
reading for each range
Response time: 98% of
full-scale reading in 5 seconds, 100% of full-scale in 15 seconds
Temperature
compensation: automatic from 5 to 35°C
Temperature range
(can be placed in): 0 to 80°C
Cell Constant: 1.0 cm-l
Description: dip
type, epoxy body, parallel carbon (graphite) electrodes
Dimensions: 12-mm OD
and 150-mm length
Using the Conductivity Probe with other Vernier Sensors
It is very important
for the user to know that the Conductivity Probe will interact with some other
Vernier sensors and probes, if they are placed in the same solution (in the
same aquarium or beaker, for example), and they are connected to the same interface
box (e.g., the same Serial Box Interface). This situation arises because the
Conductivity Probe outputs a signal in the solution, and this signal can affect
the reading of another probe.
The following probes
cannot be connected to the same interface as a Conductivity Probe and placed in
the same solution:
• Dissolved Oxygen
Probe
• pH System
• Direct-Connect
Temperature Probe
If you wish to take
simultaneous readings using any of the probe combinations listed above, here
are some alternative methods:
• To take
simultaneous conductivity and dissolved oxygen or conductivity and pH readings,
you can connect the probes to two different interface boxes. If the two probes
in question are connected to separate CBL units (or separate Serial Box
Interfaces), the two probes will read correctly in the same solution.
• The temperature
probe that comes with the Texas Instruments CBL System can be used in the same
container with the Conductivity Probe.
• If you wish to use
a Direct-Connect Temperature Probe in the same solution with the
Conductivity Probe, wrap the part of the
probe in the solution with Saran Wrap or Parafilm, to isolate the probe
electronically. The small increase in thermal mass will not significantly
decrease the response time of the temperature probe.
• If you wish to take
temperature readings along with Conductivity, the Vernier Standard
Temperature Probe (TPA-DIN, $43) or the
Vernier Quick Response Temperature Probe (TPAQ-DIN, $49) may be used in place
of the Direct-Connect Temperature Probe. Neither of these probes will interfere
with the Conductivity Probe reading.
• If you are sampling
a lake or stream and want to use two of the probes with a single interface, you
can connect the two probes in question to the same interface and load their
respective calibrations. Place one probe in the water first and take its
reading. Then remove it and place the second probe in the solution to take its
reading.
Using the Conductivity Probe in your Classes:
Experiments from
Vernier Software lab manuals: Vernier Software has several lab manuals that
have experiments that support a conductivity probe. These include:
• Chemistry with
Computers for the Macintosh
• Chemistry with
Computers for IBM
• Chemistry with CBL
• Physical Science
with Computers for Macintosh and IBM (Serial Box and ULI)
• Physical Science
with Computers (Apple II and IBM Game Port Interface)
• Biology with
Computers for Macintosh and IBM (to be released in the Summer of 1996)
Here is a summary of
some of the experiments from these manuals
Properties of Solutions:
Electrolytes and Non Electrolytes
In this experiment,
student discover some properties of strong electrolytes, weak electrolytes, and
non-electrolytes by observing conductivity values of aqueous solutions. One
part of the experiment has students measure the conductivity of three chloride
solutions with the same concentrations. The data shown here are for 0.005 M
solutions:
NaCl 721 mS
CaCl2 1251 mS
AlCl3 1650
mS
Based on these data,
students discover for themselves that each of these compounds produce different
ratios of ions when they dissociate in water. Notice that the ratio of
conductivity values (1.8 to 3.0 to 4.0) is very close to the mole ratio of ions
formed when each compound dissociates: 2 to 3 to 4. Another part of the
experiment has students place the Conductivity Probe in 0.005 M acid solutions,
arranged here from weakest to strongest:
HC2H302 142 mS Ka =
1.8 x 10-5
H3PO4 1230 mS Ka1 =
7.5 x 10-3
HCl 1990 mS Ka=
very large
Saltwater Conductivity: The Effect of Concentration
In this experiment,
concentrated sodium chloride solution is added drop-by-drop to distilled water.
After each drop is added, a conductivity reading is made, and the number of
drops recorded using a prompted (or keyboard) input. Here is some sample data
from this experiment:
Figure 3: Conductivity of saltwater vs. drops
of NaCl
Using Conductivity to Find an Equivalence Point
Students perform a
titration using the Conductivity Probe by adding 0.080 M sulfuric acid to 0.01
M barium hydroxide:
Ba2+(aq) + 2 OH-(aq)
+ 2 H+(aq) + S042-(aq) ® BaS04(s) + H2O(l)
Notice in Figure 4
that this reaction results in a minimum conductivity value at the equivalence
point, since the barium hydroxide precipitate and water products yield very few
aqueous ions.
Figure 4: Conductivity vs.
volume of sulfuric acid solution
Diffusion Through Membranes
In this experiment, a
potassium chloride or sodium chloride solution is allowed to diffuse through
dialysis tubing into distilled water. The Conductivity Probe is used to monitor
the increase in concentration as the potassium chloride diffuses through the
membrane. Sample data is shown here:
Figure 5:
Conductivity vs. time of membrane diffusion
Sampling in Streams and Lakes: It is best to sample away from shore and below the water
surface, if possible. In free-flowing streams there will usually be good mixing
of the water, so that samples taken near the current will be quite
representative of the stream as a whole. If the you are sampling an impounded
stream or a lake, there will be very little mixing—therefore, it is important
to sample away from shore and at different depths, if possible. We do not
recommend that you drop the Vernier Conductivity Probe so that the entire
electrode is submerged; the electrode is not constructed to withstand higher
pressures, so seepage into electronic components of the electrode might result.
As an alternative we recommend that you devise an extended sampling device that
allows you to reach out into a stream from shore, downward from a bridge,
or one or two feet
into the stream. Many ecology books will suggest various designs of such
sampling devices from inexpensive materials (e.g., metal rods, simple plastic
containers, golf all retrievers).
Although it is better to take readings at the collection site, readings of
total dissolved solids or conductivity should not change significantly if you
collect samples and take readings at a later time. However, be sure that
samples are capped to prevent evaporation. If sample bottles are filled brim
full, then a gas such as carbon dioxide, that is capable of forming ionic
species in solution, is prevented from dissolving in the water sample.
Since the probe has
built-in temperature compensation, you can do your calibration in the lab. This
means that even though you will be sampling in water that has a different
temperature than your calibration temperature, the probe will take correct
readings at the new sampling
temperature.
Sampling in Ocean Salt Water or Tidal Estuaries: Salt-water samples may exceed the high range of the
Conductivity Probe, 0 to 20,000 mS. Sea water from the mid-Atlantic ocean has a conductivity
value of 53,000 mS
(or a concentration of more than 27,000 mg/L as NaCl). Samples in this range
will need to be diluted in order for them to be monitored using the high range.
For example, you can take a sample of ocean water, and dilute it to 1/4 of its
original concentration by adding 100 Ml of the salt-water sample to 300 Ml of
distilled water. This diluted sample
can then be measured using the Conductivity Probe at the high-range setting. If
the conductivity value for the diluted sample is measured to be 13,000 mS, then this answer
is multiplied by a factor of 4 to obtain the conductivity value of the original
sample: 4 x 13,000 = 52,000 mS.
More about
Conductivity
Conductivity is an
easy and informative water quality test. It is sometimes used as a ‘watchdog”
environmental test—any change in the ionic composition of a stream or lake can
quickly be detected using a conductivity probe. Conductivity values will change
when ions are introduced to water from salts (e.g., Na+, Cl-),
acids (H+), bases (OH-), hard water (Ca2+, HCO3-,
C032-), or soluble gases that ionize in solution (C02,
NO2, or SO2). However, a conductivity probe will not tell
you the specific ion responsible for the increase or decrease in conductivity.
It simply gives a general indication of the level of total dissolved solids
(TDS) in the stream or lake. Subsequent tests can then help to determine the
specific ion or ions that contributed to the initial conductivity reading
(e.g., pH for H+, a titration for hard water as Ca2+, or
a colorimetric test for NO3-). If a sample is composed of only one
particular type of ion, a conductivity probe can be calibrated for that
particular ion, allowing you to determine the concentration of that ion from
conductivity readings. This can also be done if the concentration of one salt
is so high that concentrations of other salts become negligible (e.g., NaCl in
salt-water samples, or CaCO3 in hard-water samples).
State and local
regulations often place upper limits on the level of total dissolved solids in
drinking water. These levels vary from state to state, but often must be at a
level less than 1100 mg/L TDS. A conductivity probe can give a quick and
accurate reading for such a determination.
2000 mS 
conductivity
1000
mg/L
Since there is a
nearly linear relationship between conductivity and concentration of a
specification or salt, the Conductivity Probe can be used to determine the
concentration of an ion. A curve similar to the one shown here can be obtained
if you prepare or purchase standard solutions (solutions with known
concentrations). Note in the figure below the 2:1 ratio between conductivity in
mS
and TDS concentration in mg/L.
TDS Concentration
Even though total
dissolved solids is often defined in terms of this 2:1 ratio, it should be
understood that a TDS reading of 500 mg/L can have a different meaning in a
sample that is mostly NaCl than in another sample that is composed primarily of
hard water ions such as Ca2+ and HCO3-. The
relationship between conductivity and sodium chloride concentration is
approximately a 2:1 ratio and is very nearly a direct relationship. Table 1
shows some corresponding values for conductivity (mS/cm), concentration
(mg/L as NaCl), and concentration (mg/L TDS).
Conductivity probes
can provide students with important clues as to the ionic or molecular nature
of compounds. Non-ionizing molecular compounds, such as methanol, will give
readings of nearly zero conductivity. Note: Solutions that give a zero
conductivity reading will be rare. Even in very pure distilled water, ions will
be produced from dissociation of water into H+ and OH-
ions or carbon dioxide dissolving and producing HCO3-
ions. Water-soluble ionic compounds will give significant conductivity values,
the size of which depends on such factors as ionic radius, charge of ions, and
mobility of ions. Ionizing molecular compounds such as weak acids will yield
conductivity values that can be used to relate the relative strength of these
acids—an aqueous solution of a strong acid such as hydrochloric acid will give
a much higher conductivity value than a weak acetic acid solution of equal
concentration.
Table 2. Conductivity of Sodium chloride solutions as
a function of temperature.
|
Sodium chloride concentration (mg/L) |
Total dissolved solids (TDS) (mg/L) |
Conductivity (mS/cm) |
|
1.0 |
1.1 |
2.2 |
|
5.0 |
5.4 |
10.8 |
|
10 |
10.7 |
21.4 |
|
20 |
21.4 |
42.7 |
|
50 |
52.5 |
105 |
|
100 |
105 |
210 |
|
150 |
158 |
315 |
|
200 |
208 |
415 |
|
500 |
510 |
1020 |
|
1000 |
995 |
1990 |
|
1500 |
1465 |
2930 |
|
2000 |
1930 |
3860 |
|
5000 |
4482 |
8963 |
|
10250 |
9000 |
18000 |
Warranty
All Vernier
Conductivity Probes are warranted to be free from defects in material and
workmanship for a period of twelve (12) months from purchase provided the
electrode has been used in accordance with this instruction manual and used
under normal laboratory condition. The warranty does not apply when the
electrode has been subjected to accident, alternate use, misuse, or abuse in
any manner.
In the event of a
defect in material or workmanship within the twelve (12) month period, Vernier
Software will either repair or replace the electrode at no expense to the user
other than freight charges. Returned electrodes will not be accepted unless authorization
has been issued by Vernier. For warranty service, please write or call Vernier
Software directly.
Vernier Software
8565 S.W.
Beaverton-Hillsdale Hwy.
Portland, OR 97225-2429
(503) 297-5317
• FAX (503) 297-1760
dvernier@vernier.com •
http://www.teleport.com/~vernier
Flinn QuickStarts™
Conductivity Sensor (TC1146)
The Connections:
1. Connect the
Conductivity Sensor to Port 1 of the Serial Box Interface.
2. Connect the Serial
Box Interface to the COM 1 or COM2 port of the computer
using the cable
provided. (Use the 9-pin to 25-pin adapter if necessary.)
3. Plug the Serial
Box Interface into an electrical outlet using the AC adapter.
The Set-up/Customizing Data Loggers:
1. Open the Data
Logger program. Click on Start, Program, Vernier, LoggerPro.
Note: If the
message “Warning! Cannot find the interface box” appears;
a) Check all
connections,
b) Determine which
port (COM1 or COM2) is accepting the cable from the Serial Box
Interface, and
c) Click on the
appropriate button (“COM1” or “COM2”).
A default graph
called “Untitled-1” will appear. Data Logger does not currently contain a
prepared experiment file for the Dissolved Oxygen Sensor, so it is necessary to
prepare one.
The right mouse button is used only to access Data Logger
menus. Use the left mouse button for all other operations.
3. From the list,
double-click on “Conductivity Probe”,
open the file for the Conductivity Measurements. You may need to scroll the
list by clicking on the left mouse button and dragging the cursor across the
list to find these files.
4. The “Setup” menu can be used to specify
Sensor [Sensor setup, Calibration, and Details(units
can be specified here)]
Data Collection
[Mode, Sampling (Rate)]
and Interface details (Com port).
5 Customize the axes:
a) Double-click
anywhere on the graph. This causes the “Axes” dialog box to appear.
b) Click and hold the
cursor or the y-axis label (which currently reads “Pl & P2”). Move the
cursor to “Port 1” and release the mouse button.
c) To change the
y-axis range, simply double-click inside the upper and/or lower limit value box
and enter the desired value. (Use 20,000 mS to begin.)
d) The x-axis should
already be in units of “Time.” You may change the x-axis range in the same
manner as you did for the y-axis above.
e) Click”OK”.
4. Under the
“Display” menu, choose “Labels & Units”.
a) Double-click in
the box for Port 1 under “Long Name” and enter “Conductivity”.
b) Double-click in
the box under “Short Name” and enter “Cond.”.
c) Double-click in
the box under “Units” and enter ‘’mS/cm’’
Calibration:
It is recommended
that the Conductivity Sensor be calibrated with each use. First, soak the lower
portion of the sensor in distilled water for 10 minutes to remove any residues.
Set the toggle switch on the Conductivity Meter for “0-20,000 mS”.
1. Under the
“Experiment” menu, choose “Calibrate...”.
2. The program will
ask, “How would you like to calibrate the probes?” Click on “Calibrate Now”.
3. The program will
ask “Which ports would you like to calibrate?” Click on “Port 1 Only”.
4. Take the probe out
of the distilled water and hold it in the air. Once the voltage shown on the screen
stabilizes, click on “Stable”. The program will ask for the stable reading:
enter “0” for the conductivity. Click on “OK”.
5. Place the
Conductivity Sensor into your 0.02N potassium chloride standard solution. Be
sure the hole of the sensor is completely submerged. When the voltage
stabilizes, click on “Stable”. Enter “2768” for the conductivity of the
standard solution. Click on “OK”.
Using the Conductivity Sensor:
1. Rinse the sensor
with distilled water, and insert the tip of the probe into the solution being
tested.
2. While gently
swirling the probe in the solution, click “Start” to take readings. Click
“Stop” to discontinue data collection.
3. Rinse the sensor
with distilled water before taking another measurement.
4. When finished,
rinse the Conductivity Sensor with distilled water and blot it dry using a
paper towel or lab wipe. The probe can be stored dry.