3
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
The Go Direct Tris-Compatible Flat pH Sensor 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
pH is measured potentiometrically when using an electrode. In other words,
your measurement is based on an electrical signal. A potential develops across
the glass membrane of a pH electrode when it comes in contact with a solution.
This potential varies as the pH varies, but requires a constant second potential
to compare the changes against. This is the function of the reference electrode,
to provide a constant potential, regardless of pH.
In acidic or alkaline solutions, the voltage on the outer membrane surface
changes proportionally to changes in hydrogen ion activity by the Nernst
equation:
E = E
o
+ (2.3RT/nF) log [H
+
]
Where:
E = total potential difference (measured in mV)
E
o
= standard potential
R = gas constant
T = temperature in Kelvin
N = number of electrons
F = Faraday's constant
[H
+
] = hydrogen ion activity
Troubleshooting
The Vernier gel-filled Go Direct Tris-Compatible Flat pH Sensor is designed to
make measurements in the pH range of 0 to 14. The gel-filled reference half cell
is sealed; it cannot be refilled.
The pH Sensor is designed to be used in aqueous solutions. The polycarbonate
body of the sensor can be damaged by many organic solvents. In addition, do
not use the sensor in solutions containing: perchlorates, silver ions, sulfide ions,
Shaft diameter
12 mm OD
Resolution
0.01 pH
USB specification
2.0
Wireless specification
Bluetooth 4.2
Maximum wireless range 30 m
Dimensions
EA: 8.5 cm height × 3 cm wide × 1.75 cm depth
pH: 15.5 cm length, 12 mm OD
Battery
300 mA Li-Poly
Battery life (single full
charge)
~24 hours
Battery life (long term)
~500 full charge cycles (several years depending on
usage)
Care and Maintenance
Short-term storage (up to 24 hours):
Place the electrode in pH 4 or pH 7 buffer
solution. It should never be stored in distilled water.
Long-term storage (more than 24 hours):
Store the electrode in a pH 4
buffer/KCl storage solution in the storage bottle. The pH electrode is shipped in
this solution. Vernier sells 500 mL bottles of pH Storage Solution (order code
PH-SS), or you can prepare additional storage solution by adding 10 g of solid
potassium chloride (KCl) to 100 mL of pH 4 buffer solution. Vernier sells a pH
Buffer Capsule kit (PH-BUFCAP) that includes a buffer solution preservative.
Storing the electrode in this solution contributes to electrode longevity and
retains electrode response time when the unit is placed back into service.
If the electrode is inadvertently stored dry for a short period of time, immerse the
tip in the pH 4 buffer/KCl storage solution for a minimum of 8 hours prior to
use. If the readings are still not accurate after calibration or if the response is
slow, try shocking the sensor as described in the Troubleshooting section.
Battery Information
The Go Direct Tris-Compatible Flat pH Sensor 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 the Go Direct Tris-Compatible Flat pH Sensor 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.