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Q: Can I use a Sensorex
pH electrode with any meter or controller ?
A:
Yes. The output signal and impedance of all pH/ORP electrodes
are compatible with virtually all meter and controllers. When
ordering, please specify the type of connector, the temperature
compensation (if using Automatic
Temp Comp), and the installation configuration (if installing
in a tank or pipe).
Q:
Does Sensorex make Calomel pH electrodes ?
A:
No. Due to the hazardous materials (Mercury and mercurous
compounds) used in Calomel electrodes, Sensorex has developed
a superior pH electrode using non-hazardous materials. Calomel
electrodes were primarily used in applications involving proteins,
sulfide, Mercaptan and silver ions. These materials react with
the silver ions in the typical reference solution/gel and precipitate
at the reference junction, plugging the junction, creating a reference
junction potential, and/or contaminating the reference solution/gel.
Sensorex offers a double junction design with no silver or chloride
ions in contact with the sample. The classical problems (hysteresis,
instability, and short life at elevated temperatures) characteristic
of Calomel electrodes are eliminated with the Sensorex Double
Reference Junction design.
Q:
Are Sensorex's pH electrodes compatible with Tris Buffers ?
A:
However, if your application involves proteins, a Sensorex
double junction electrode is recommended. Proteins will react
with the silver ions in the typical reference solution/gel and
precipitate at the reference junction, plugging the junction,
creating a reference junction potential, and/or contaminating
the reference solution/gel. Sensorex offers a double junction
design with no silver or chloride ions in contact with the sample.
If your application involves low ionic (less than 100 microsiemens)
samples, Sensorex also has a low ionic electrode which will provide
greater stability and longer life in these applications. Contact
the factory for these specific applications.
Q:
How should I store my pH electrode when not in use ?
A:
Each Sensorex pH electrode is supplied with a soaker bottle
or storage cap containing soaker/storage
solution. If you no longer have the solution, you can purchase
it by pint bottles from Sensorex (part number S16). If
soaker solution is not available, you can use the following in
order of preference:
4 pH Buffer
7 pH Buffer
Tap Water
Note:
Do not store any pH electrode in DI water. DI water
is for rinsing, not storing.
Q:
I am having difficulty measuring low ionic samples and DI water
?
A:
Standard pH electrodes contain 3.5M KCl as a reference
gel. Samples like DI water and other low ionic solution contain
very small amounts of salt. These solutions try to leach ions
from the reference gel to raise their conductivity levels. This
results in very slow, sluggish and unstable readings from a conventional
pH electrode. Sensorex offers any standard double junction electrode
in a special low ionic configuration which addresses these measurements
difficulties. Contact Sensorex for more details.
Q:
How long can I run my pH electrode cable ?
A:
All pH electrodes provide a high impedance millivolt signal.
This signal is amplified by a pre-amp. The pre-amp is typically
built into the instrument or controller, but can be a separate
component or even built into the electrode. Normally, cable runs
under 25 feet are not a problem for the millivolt pH signal. If
you want to ensure a strong signal or need long cable runs, the
Sensorex pHAMP-1 battery powered amplifier can ensure quality
signal transmission. Contact
Sensorex for more details.
Q:
How is your flat surface pH electrode self-cleaning ?
A:
Using a flat measuring surface in agitated turbulent flow
will minimize coating problems on the measuring surface of the
electrode. The coating tends to move off the measuring surface
since the entire surface is exposed to flowing sample. Normal
spherical bulb measuring surface have a dead flow area which promotes
coating buildup. See our Operating
Principles section or contact Sensorex for details.
Q:
What is the output of Sensorex pH electrodes ?
A:
Sensorex and all manufacturers' pH electrodes conform
to the Nernst Equation for pH output as a function of temperature.
At 25 degrees C, the pH output is 59.16 millivolts/pH unit. The
electrode will give zero output at a pH of 7.0 at all temperatures.
Q:
What is the temperature effect on pH glass impedance ?
A:
pH glass impedance goes up as temperature goes down by
a factor of 2.5 times for each 10 degrees C change in temperature.
For example, if the glass impedance is 100 Megaohms at 25 degrees
C, it will be 250 Meg ohms at 15 degrees C. Higher impedance slows
down the electrode's speed of response to changing pH levels.
This is characteristic of all pH electrodes.
Q:
How do I know when to replace my pH electrode ?
A:
As a pH electrode ages, the impedance of the pH sensitive
glass increases causing the output signal to become slow, sluggish,
or drifting. Zero will shift beyond the adjustable range and span
will shorten. In most typical applications, a pH electrode will
function for 6 to 24 months. However, in fluoride applications
or very caustic applications, the typical pH glass has a much
shorter life. See our section on Fluoride Resistant electrodes
for these applications.
Q:
I have calibrated my meter, but when I attach the pH electrode,
the reading is off. What's wrong?
A:
All pH electrodes will have a small amount of offset as
manufactured. The zero adjustment on your meter is designed to
correct this offset. Consequently, you must calibrate the meter
and electrode together, as a system. Sensorex supplies a pH
Checker to calibrate or isolate a problem to your meter or
electrode. But final calibration must be performed with the electrode
connected to the meter. Sensorex also supplies buffers
for performing pH and REDOX system calibrations.
Q:
My new pH electrode is unstable and/or has an offset when installed
in my system.
A:
The most common cause for this problem is an electrical
ground loop in your system. To verify this problem, remove the
electrode and calibrate it with a known buffer solution in a beaker.
If the electrode measures within specification (stable and adjustable
zero) when calibrated, place a copper wire in the beaker and the
other end in your system. If the reading become unstable or shifts,
a ground loop is your problem.
The source of the ground
loop could be any motor, pump, conductivity probe, or other electrically
powered device in the media with the pH electrode. Do not attach
the conductivity probe or any other electrically powered device
to the same ground on your meter or controller as the pH electrode.
You can also try placing a large (12-14 AWG) copper conductor
into the media and the other end to the meter/controller ground
terminal to draw the ground loop away from the pH electrode. See
our section on Ground
Loop Interrupt pH electrodes for other solutions.
Q:
Why does my pH electrode give slow, sluggish, drifting, unrepeatable
readings ?
A:
There are three possibilities to explain these observations:
- the electrode sensing surfaces may be coated
- the electrode may be reaching its useful life (typically 6
to 24 months)
- a low ionic (conductivity below 100 microsiemens) media is
being measured.
Call Sensorex for our
special low ionic pH electrodes or specify low ionic application
on the order form.
Q:
How can I clean a coated pH glass electrode ?
A:
A 2% - 5% hydrochloric acid (HCl) solution will dissolve
most coatings. It is best to use a cleaning chemical that
will dissolve the coating on the pH glass but not harm the materials
of construction of the pH electrode. Refer to the product
specifications for materials of construction.
Q:
Do I need a Double Junction Reference in my electrode ? A:
If your application includes proteins, heavy metals (Ni,
Cd, Cu, Cr, Ag), sulfides, cyanides or iodides or any other material
which will react with silver or chloride ions, a Double Junction
electrode will provide added protection and last longer. |
