In-Situ pH Sensor User Manual

Innovations in

Innovations in

Water Monitoring

Water Monitoring

pH Sensor

Part Number 0059510

Description

The In-Situ® Inc. pH sensor is a combination, single­junction electrode that contains a replaceable junction
and rellable reference electrolyte solution. The pH
sensor is designed and manufactured for long-lasting,
accurate results in a variety of environmental waters.

Installation

The TROLL 9500 may be shipped with a pH sensor
installed. If installation is necessary, unpack and install
the sensor in port 1 or 3 of the TROLL 9500, Figure 1.

1. Remove the restrictor or Cal Cup from the front
end of the TROLL 9500. This allows access to the
sensor block.

2. Remove the sensor hydration bottle and set aside
for future storage of the sensor.

3. Rinse the sensor with clean water.

4. Remove any moisture or dirt from the area around
the port where you will install the sensor, then use
the sensor removal tool to remove the plug from
the port. Retain the plug for future use.

5. Remove any moisture or dirt from the port
connector with a clean swab or tissue.

6. Remove the cap from the sensor connector. Check
lubrication of the sensor o-rings. If the o-rings
appear dry, apply silicone lubricant, provided in the
sensor box, before installation.

7. Visually align the sensor connector pins with the
port connector pins.

8. Press the sensor firmly into the port until you feel
it dock with the port connector. When properly
inserted, a small gap (the width of the sensor
removal tool) remains between the instrument
body and the widest part of the sensor, for ease
of removal.

Instruction Sheet

Technical Note

Calibration

Although pH may be calibrated with Quick Cal (1
point at pH 7), for best results In-Situ recommends a
2- or 3-point calibration. These options are available in
the software:

• Traditionalcalibration–1point:requires a single
solution; results in calculation of sensor oset for a
single pH value (pH 4, 7, or 10). Select a calibration
solution for the pH range you expect to measure.

• Traditionalcalibration–2point:requires 2
solutions; results in calculation of sensor slope and
oset for one pH range (pH 4-7 or pH 7-10). Choose
solutions for the pH range you expect to measure.

• Traditionalcalibration–3point:requires 3
solutions; results in calculation of slope and oset
for 2 ranges (pH 4-7 and pH 7-10). The correct
slope for the pH values being monitored will
automatically be applied.

• DefaultCoecients: Resets factory defaults to the
sensor. No solutions are required.

Calibration Procedure

Figure 1. TROLL 9500 pH Sensor Positions

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1. Fill the Cal Cup to the ll line with the selected
calibration solution and attach to the instrument.

a. With a full set of sensors installed, ll to the

lower line. With one or two sensors installed, ll
to the upper line.

2. Connect the instrument to a PC, open Win-Situ 4 or
Pocket-Situ 4 software, and click Find to connect to
the device. Select the instrument in the Navigation
tree. The software will automatically detect and
display the installed sensors.

3. Click Parameters, select pH, then click Calibrate.

Figure 2. Win-Situ 4 Calibration

4. In the pH Calibration Wizard, specify how many
calibration points you intend to use, and the
solution for each. Click Next and follow the wizard
to perform a 2- or 3-point calibration. Be sure to
rinse the Cal Cup and sensors between solutions.

5. At the end of the Wizard, click Finish to write the
newly calculated calibration coecients to the
sensor. The pH sensor is now calibrated and ready
to use.

If the instrument will be used in a day or so, leave the
sensors installed. Remove the Cal Cup and rinse it and
the sensors. Add about 50-100 mL of tap water to the
Cal Cup. Return the probe to the Cal Cup for transport
to the eld site.

• For best results, try to calibrate at the same
temperature as the expected sample temperature.

• Prior to calibrating, rinse the Cal Cup and the front
end of the TROLL 9500 in clean water, and shake
dry. For best results, follow this with a second rinse
in a portion of the calibration solution.

• The Cal Cup ll line indicates the approximate
amount of solution to use. Fill to the upper line with
1-2 sensors installed; ll to the lower line with more
sensors installed. The temperature sensor should be
submerged at least one half inch.

• Most sensors stabilize in 1 to 3 minutes if
properly hydrated before calibration. To minimize
stabilization time, do not handle the instrument
during calibration readings.

• To shorten the calibration time, you have the option
to accept the calibration when stability is “Nominal.”
If the early value is accepted, the calibration point
will be designated “USER SET” in the calibration
report. If the calibration was performed through to
stability then the sensor will operate according to
specications.

• Cal solutions may be ushed down the drain with
running water, or saved in a separate container and
used to rinse the next time you calibrate with the
same solution.

• A calibration report in HTML format is created for
each calibration—even one that was cancelled. You
can view the report right after calibrating, or at any
time. See “Calibration History” in Section 10 of the
TROLL 9500 Operator’s Manual for details.

• Calibrate the sensor after replacing the reference
junction and/or the lling solution, during routine,
scheduled maintenance, or every 2-6 weeks in the
absence of other indicators.

Indicators During Calibration:

NOTTESTED is displayed until Run is selected.

UNSTABLE indicates the sensor response does not

meet the criteria for a valid calibration point.

Calibration Notes:

NOMINAL indicates the sensor deviation meets early

• pH 4, pH 7, and pH 10 buers are available from
In-Situ Inc. for pH calibration. Always begin with the
lowest buer value when performing a multi-point
calibration.

• Ensure that every port is lled with a sensor or a
plug before calibrating.

stabilization criteria. The Accept button becomes
available when stability is nominal. You may accept the
early value, or wait for complete stability. If you accept
the early value, the calibration point will be designated
“USER SET” in the calibration report.

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STABLE is displayed when the readings have stabilized.
The calibration automatically proceeds to the next screen.

• Temperature and barometric pressure may be
displayed for some calibrations.

• Sensor Reading: The current sensor response in
indicated units.

• Sensor Deviation: Change in sensor response
between the last two readings.

Resetting Default Coefficients

Sensor calibration may be reset to factory defaults at
any time. This option is most eective when the sensor
is new.

1. With a pH sensor installed, establish a connection to

2. Select pH in the Parameters list and click Calibrate.

3. In the rst screen, select Use Default Coecients,

4. In the nal screen, click Finish to send the values to

the instrument in Win-Situ 4 or Pocket-Situ 4.

then Next.

the sensor.

• Temperature compensation is provided in the
software to account for measurements taken
at temperatures dierent from the calibration
temperature. For most accurate results, try to
calibrate at the same temperature as the expected
sample temperature.

• After an initial 1-2 week settling period, during
which the sensor should be calibrated weekly,
calibration frequency will depend on the nature
of the sample and degree of accuracy required. In
clean water samples, the pH sensor should retain
its accuracy specication for 2-6 weeks before
requiring calibration.

• A small error in pH will occur in basic solutions
(>pH 10) that contain high levels of sodium salts
(>0.01M) due to sodium interference.

• pH readings in pure water samples (<100µS/cm
conductivity—also known as “low ionic strength”
samples) require up to 20 minutes after calibration
to stabilize and begin producing accurate results.
After calibration, condition the sensor in a low
conductivity solution.

Sensor Slope and Offset

The pH calibration curve pivots around pH 7 (0 mV
response). The oset calculated by the software when
calibrating at pH 7 will typically be between 350-450 mV.
If the oset falls outside these limits, replace the lling
solution or the junction.

The slope should fall between -54 mV/pH and -62 mV/pH.
A calculated slope greater than -50 mV/pH or less than -66
mV/pH indicates that the sensor requires maintenance.

Usage Recommendations

Sensor Handling and Storage

Routine Maintenance

After the pH sensor is moistened, it must be kept moist
for the life of the sensor.

The pH sensor ll solution has a shelf life of 2 years.
Replace the ll solution every 5 to 6 months or when:

• The sensor fails to calibrate within the acceptable
slope and oset range.

• Sensor readings vary.

• Readings during calibration at pH 7 are greater than

+30 mV or less than -30 mV.

• Sensor is slow to respond.

Note: If the sensor fails to calibrate after you replace the ll

solution, replace the reference junction.

Replacing the Filling Solution

1. Use the sensor removal tool to pry the sensor up
and out of the instrument.

2. Unscrew the reference junction. See Figure 4.

3. Protect the connector end of the sensor with

Figure 3. pH sensor calibration graph

Figure 4. pH sensor with reference junction removed

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the dust cap it shipped with, or wrap the sensor
in a paper towel to prevent lling solution from
entering the electrical connector.

4. Hold the sensor at an angle and shake out the old
lling solution.

5. Using the dispenser cap on the lling solution
bottle, insert the tube into the bottom of the empty
reservoir as shown. Squeeze a steady stream of
solution into the reservoir until it overows and no
bubbles are observed. Continue to add solution
while pulling the tube out of the reservoir.

6. Attach the reference junction to the sensor and

Figure 5. Fill the pH reservoir

To clean the pH sensor, gently rinse with cold water.
If further cleaning is required, consider the nature of
the fouling.

To remove crystalline deposits:

• Clean the sensor with warm water and mild soap.

• Soak the sensor in 5% HCI solution for 10 to 30 minutes.

• If deposits persist, alternate soaking in 5% HCI and

5% NaOH solutions.

To remove oily or greasy residue:

• Clean the sensor with warm water and mild soap.

• Methanol or isopropyl alcohol may be used for

short soaking periods, up to 1 hour.

• Do not soak the sensor in strong solvents, such
as chlorinated solvents, ethers, or ketones,
including acetone.

To remove protein-like material, or slimy lm:

• Clean the sensor with warm water and mild soap.

• Soak the sensor in 0.1M HCI solution for 10 minutes

and then rinse with deionized DI water.

hand-tighten until snug, rmly seating the junction.
Some lling solution will overow. Wipe the excess
o the sensor body.

7. Soak the sensor in tap water for at least 15 minutes.

8. Calibrate the sensor.

Note: If necessary, thoroughly clean the sensor connector to

remove lling solution: Using a disposable pipette, ll the
connector with isopropyl alcohol (70% - 100%). Shake to
dry. Repeat 3 times. Dry overnight. When thoroughly dry,
calibrate the sensor.

Replacing the Junction

Replace the junction when the sensor fails to calibrate
with a reasonable slope and oset, even after replacing
the lling solution.

1. Unscrew the reference junction and discard.

2. Replace the lling solution and screw in a new
reference junction.

3. Soak for 15 minutes, then calibrate the sensor.

Note: Keep the junction damp at all times to avoid a lengthy

rewetting process.

After performing any of these cleaning methods, rinse
the sensor with water, then soak overnight in pH 4 buer.

Sensor Removal

You can store the pH sensor on the TROLL 9500, or you
can remove the sensor. If you remove the sensor from
the instrument, seal the port with a port plug and place a
dust cap on the port side of the pH sensor.

To remove the sensor, use the sensor removal tool to
pry the sensor upward and outward.

Short-term Storage

Up to 1 week: Fill the electrode storage bottle with pH 4
buer and immerse the sensor tip in the buer. Tighten
the cap to prevent drying. Alternatively, pH 7 buer can
be used for a few days.

Long-term Storage

Greater than 1 week: Fill the electrode storage bottle with
10-20 mL of storage solution (Order No. 0065370) and
immerse the sensor. Tighten the cap to prevent drying.

Cleaning

Begin with the most gentle cleaning method and
continue to the other methods only if necessary. Do not
directly wipe the glass bulb.

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Storage Recommendations

Prior to using the pH sensor after long-term storage, rinse the sensor with DI water and then soak it in pH 4 buer
for 1 or 2 hours. This will saturate the glass bulb with hydrogen ions and prepare it for use.

Do not store the pH sensor in DI water because it will deplete the reference solution and drastically reduce the life
of the sensor.

Specifications

Type: Glass sensing bulb with Ag/AgCl reference half-cell, replaceable single junction,
replaceable reference lling solution

Range: 0 to 12 pH units

Pressure Rating: 211 m (692 ft)

Accuracy: ± 0.1 pH unit

Resolution: 0.01 pH unit

Operating Temperature: 0 to 50° C (32 to 122° F)

Replacement Parts

Reference Filling Solution (60 mL)................................................................................................................................................0056900

pH Calibration Kit (1 L each pH 4, pH 7, pH 10, DI water)......................................................................................................0032080

Quick Cal (4 x 250 mL).......................................................................................................................................................................0033250

Reference Junction Kit (3 junctions, 60 mL reference lling solution...............................................................................0059620

Storage Solution (500 mL)................................................................................................................................................................0065370

For more information, contact In-Situ Inc.

221 East Lincoln Avenue, Fort Collins, CO 80524
1-800-446-7488 (toll-free in U.S. & Canada)
1-970-498-1500 (international & domestic)

www.in-situ.com

Information subject to change without notice. In-Situ, In-Situ logo, Baro Merge, BaroTROLL, HERMIT, RDO, Pocket-Situ, RuggedCable, RuggedReader, TROLL, and Win-Situ are
trademarks or registered trademarks of In-Situ Inc. © 2011. All rights reserved.

0059512 rev. 003 04/12

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