Page 1
Signet 275X Series Wet-Tap DryLoc® pH and ORP Electrodes
Signet 276X Series Diff erential DryLoc® pH and ORP Electrodes
Signet 277X Series Threaded DryLoc
®
pH and ORP Electrodes
*3-XXXX.090*
3-2764.090 Rev 12 12/19
Operating Instructions
Description
The Signet General Purpose 275X Wet-Tap and High Performance 276X and 277X series
of pH and ORP electrodes are designed to minimize maintenance time and maximize
performance longevity and value. All three family of pH and ORP electrodes are memory
chip enabled to store Manufacturing, Calibration and Operational Data. For more fl exibility
and unique features, pair any pH or ORP electrode with a 2751 Smart Sensor Electronics
and the 9900 Transmitter, 9950 Dual Channel Transmitter or the 0486
Profi bus Concentrator.
The 275X Wet-Tap electrodes are all-purpose sensors ideal for applications where the probe
can be removed for cleaning and maintenance without the system shutdown. They feature a
unique foul-proof DryLoc
with the Signet 2751 Smart Sensor Electronics, and 2760 Preamplifi er. These dependable
and highly responsive electrodes feature a large reference chamber and intelligent
positioning of internal elements that combine to extend the service life. The electrodes
are o ered with a bulb sensing element that can be used for general purpose applications
where a fast response is required even at low temperatures. The choice of a Pt1000 or
3 K temperature sensor allows compatibility into all Signet pH/ORP instruments. The 3719
Wet-Tap assembly allows installation and removal of electrode even under process pressure
without the need for process shutdown.
®
connector with gold-plated contacts, designed specifi cally for use
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California Prop. 65
WARNING:
Cancer and Reproductive Harm
www.p65warnings.ca.gov
The Signet 276X Series Di erential pH and ORP electrodes feature a Ryton® body and
PTFE reference junction to resist fouling, clogging and chemical attack under harsh
chemical applications. The Di erential electrodes use a 3-electrode technique, measuring
the pH and reference electrodes against a ground electrode for a more stable output signal.
The solution ground eliminates noisy measurements by draining electrical current away from
the reference electrode. The reference electrode is housed in a glass half-cell embedded
in the reference chamber to protect it from poisioning or contamination. The electrolyte
chamber is refi llable and the salt bridge is fi eld replaceable.
The Signet 277X Series pH and ORP electrodes are highly responsive electrodes featuring
a PTFE double reference junction, potassium nitrate, KNO3, in the front chamber (to block
various poisoning ions such as copper (Cu2+), lead (Pb2+), mercury (Hg2+)) and a large
reference chamber. The two chambers combine to extend the service-life of the electrode.
Both the 276X Series and the 277X Series feature a unique foul-proof DryLoc® connector
with gold-plated contacts designed specifi cally for use with the Signet 2751 Smart Sensor
Electronics and 2760 Preamplifi er. They are available with either fl at or bulb style sensing
elements. The bulb versions can be used for general-purpose applications. The fl at versions
allow sediment and particles to sweep past the measurement surface, minimizing risks of
abrasion, breakage and coating. All versions can be installed at any angle. The temperature
device in the pH electrodes is positioned at the tip of the measurement surface, resulting in
a temperature response of less than 1 minute. Temperature devices available include 3 K,
or Pt1000 RTD.
Page 2
Warranty Information
218 mm
(8.57 in.)
35 mm
(1.4 in.)
11.9 mm
(0.47 in.)
Chemical Compatibility
Refer to your local Georg Fischer Sales o ce for the most
current warranty statement.
All warranty and non-warranty repairs being returned must
include a fully completed Service Form and goods must be
returned to your local GF Sales o ce or distributor. Product
returned without a Service Form may not be warranty replaced
or repaired.
Signet products with limited shelf-life (e.g. pH, ORP, chlorine
electrodes, calibration solutions; e.g. pH bu ers, turbidity
standards or other solutions) are warranted out of box but not
warranted against any damage, due to process or application
failures (e.g. high temperature,
mishandling (e.g. broken glass,
chemical poisoning, dry-out) or
damaged membrane, freezing
and/or extreme temperatures).
Product Registration
Thank you for purchasing the Signet line of Georg Fischer
measurement products.
If you would like to register your product(s), you can now register
online in one of the following ways:
• Visit our website www.gfsignet.com.
Under Service and Support click on
Product Registration Form
• If this is a pdf manual (digital copy),
click here
Safety Information
The retaining nuts of pH and ORP sensors are not designed
for prolonged contact with aggressive substances.
Strong acids, caustic substances and solvents or their
vapor may lead to failure of the retaining nut, ejection of the
sensor and loss of the process fl uid with possibly serious
consequences, such as damage to equipment and serious
personal injury. Retaining nuts that may have been in
contact with such substances, e.g. due to leakage or spilling,
must be replaced.
• The use of this product assumes
operators are trained and familiar
with this type of device.
• Operators should be knowledgeable
of the potential risks associated with
pressurized piping systems.
• Operators MUST follow all
necessary safety procedures.
Dimensions
2756 Wet-Tap pH
2757 Wet-Tap ORP
Electrode
1. Use appropriate eye, face, hand, body and/or
respiratory protection when using chemicals or solvents.
2. Prior to installation or removal:
• Depressurize and vent system
• Drain below sensor level.
3. Confi rm chemical compatibility before use.
4. Do not exceed the max. temperature/pressure
specifi cations.
5. Do not alter product construction.
If installing into a threaded connection:
6. Inspect threads to ensure integrity. Do not install a sensor
that has damaged threads.
7. Apply PTFE tape to the 3/4" M-NPT or ISO 7/1-R 3/4 process
connection threads in accordance with industry practices.
8. HAND TIGHTEN the sensor into the process connection.
DO NOT USE TOOLS.
Caution / Warning / Danger
Indicates a potential hazard.
Failure to follow all warnings may lead to equipment damage, injury, or
death
Personal Protective Equipment (PPE)
Always utilize the most appropriate PPE during installation and service of
Signet products.
Pressurized System Warning
Sensor may be under pressure, take caution to vent system prior to
installation or removal.
Failure to do so may result in equipment damage and/or serious injury.
Hand Tighten Only
Overtightening may permanently damage product threads and lead to
failure of the retaining nut.
Do Not Use Tools
Use of tool(s) may damage product beyond repair and potentially void
product warranty.
Note / Technical Notes
Highlights additional information or detailed procedure.
Do Not Freeze
Products are temperature sensitive and may contain freezable liquids.
Freezing damage to pH, ORP, and Chlorine electrodes voids product
DO NOT
warranty.
FREEZE
Signet 276X Series
Differential Electrode
35.3mm
(1.39 in.)
85.3mm
(3.36 in.)
1 in.
NPT
45mm
(1.8 in.)
Lubricate o-rings
with a non-petroleum
based, viscous lubricant
(grease) compatible
with the system.
Signet 277X Series
Bulb Electrode
35.3mm
(1.39 in.)
85.3mm
(3.36 in.)
¾ in.
NPT
43mm
(1.7 in.)
Signet 277X Series
Flat Electrode
35.3mm
(1.39 in.)
85.3mm
(3.36 in.)
32.6mm
(1.28 in.)
¾ in.
NPT
2
Signet 275X, 276X, 2777X Series pH and ORP Electrodes
Page 3
Specifi cations
276X Series Diff erential Electrodes
277X Series Threaded Electrodes
General
Compatibility ......................... Signet 2751 and 2760
Shipping Weight ................... 0.25 kg (0.55 lbs.)
Operating Range
276X Series ......................... 0 to 14 pH, ± 1500 mV ORP
277X Series .......................... 0 to 14 pH, ± 2000 mV ORP
Reference Electrolyte
276X Series ......................... Bu ered KNO
277X Series ......................... KCI/AgCl gel with KNO
bridge
Reference Element
276X Series .......................... pH glass electrode
277X Series .......................... Ag/AgCl
Temperature Sensor
276X Series pH .................... 3 K or Pt1000 RTD
277X Series pH .................... 3 K or Pt1000 RTD
276X Series ORP ................. 10 K ID for Signet instruments;
277X Series ORP ................. 10 K ID for Signet instruments
3 solution
3 salt
bar
6.89
pH/ORP Electrodes
276X Series and 277X Series
psi
Pressure vs. Temperature
100
6
80
60
4
40
2
20
0 40 50 60 70
°C
32 122
°F
277X Series
0 °C to 85 °C @ 6.89 bar
(32 °F to 185 °F @ 100 psi)
10 20 30
276X Series ONLY
90 100 80
212 176 50 86
Wetted Materials
Body ..................................... Ryton
®
Reference junctions .............. PTFE
Sensing surface .................... Glass (pH), Platinum (ORP)
O-rings .................................. FKM
Solution ground .................... Carbon graphite
(276X series only)
Operating Temperature
276X Series .......................... 0 °C to 95 °C (32 °F to 203 °F)
277X Series .......................... 0 °C to 85 °C (32 °F to 185 °F)
Storage Temperature ............ > 0 °C (32 °F)
Max Operating Pressure ..... 6.89 bar (100 psi)
275X Series Wet-Tap Electrodes
General
Compatibility ......................... Signet 2751 and 2760
Shipping Weight ................... 0.25 kg (0.55 lbs.)
Operating Range .................. 0 to 14 pH, ± 1500 mV ORP
Reference Electrolyte ........... Polymerized Acrylamide Gel
Wet-Tap electrolyte ............... 3.5 M KCl
Reference Element ............... Ag/AgCl
pH Temp Sensor ................... Pt1000 RTD or 3 K Balco
ORP Identifi cation ................. 10 K ID for Signet instruments
Wetted Materials
Wet-Tap body ....................... PAS (Poly Aryl Sulphone)
Wet-Tap Junctions ................ Porous PTFE
Sensing surface .................... Glass (pH), Platinum (ORP)
O-rings .................................. FKM
Standards and Approvals
• CE, WEEE, RoHS Compliant
• Manufactured under ISO 9001 for Quality,
ISO 14001 for Environmental Management and
OHSAS 18001 for Occupational Health and Safety.
China RoHS (Go to www.gfsignet.com for details)
Declaration of Conformity according to FCC Part 15
This device complies with Part 15 of the FCC rules.
Operation is subject to the following two conditions:
(1) This device may not cause harmful interference, and
(2) This device must accept any interference received,
including interference that may cause undesired operation.
REACH Information Obligation: in accordance with Article 33
of the European REACH Regulation (EC) No. 1907/2006, the
substances Lead and Acrylamide are present in the glass
matrix and as a polymerized gel respectively; in a concentration
>0.1% (w/w). During normal use, the articles do not pose any
risks and no additional information is required for safe use.
Temperatures
Operating Temperature ......... 0 °C to 85 °C (32 °F to 185 °F)
Storage Temperature ............ 0 °C to 85 °C (32 °F to 185 °F)
Maximum Temperature and Pressure rating
6.89 bar @ 0 °C to 65 °C (100 psi @ 32 °F to 149 °F)
4.00 bar @ 65 °C to 85 °C (58 psi @ 150 °F to 185 °F)
Ryton® is a registered trademark of Chevron Phillips Chemical
Signet 275X, 276X, 2777X Series pH and ORP Electrodes
3
Page 4
In-Line Installation
1. 2774 and 2775 electrodes can be mounted at any angle
2. Di erential (276X series) electrodes must be mounted at a
downward angle (> 15° from horizontal)
3. 275X Wet-Tap electrodes must be mounted in a 3719
Assembly at any angle
4. Avoid air pockets and sediments
5. Select a Signet installation fi tting (0.5” to 4” size range) for
convenience. Lightly lubricate o-ring with a non-petroleum
based lubricate (grease) compatible with the system.
6. Use the ¾ in. M-NPT or ISO 7/1-R ¾ threads on the electrode
body to install the electrode into reducing tee fi ttings.
7. Inspect threads to ensure integrity. Do not install an electrode
with damaged threads.
8. Apply PTFE tape to the M-NPT or ISO 7/1-R ¾ process
connection threads, in accordance with industry standards.
9. Use piping installation hardware with smooth,
well-fi nished threads to facilitate the installation.
10. If necessary, the pipe should be plumbed with a depression
(trap) so liquid is maintained around the electrode tip.
11. Hand-tighten the electrode into the process connection.
Do not use any tools to install the electrode.
The use of wrenches, pliers or similar may over-stress the
sensor body and lead to breakage and
subsequent spillage of the process liquid.
CAUTION:
A broken sensor may be ejected
forcefully from the fi tting and can cause
severe injury.
12. The safety instructions have an
adhesive label and should be placed
near the sensor.
NOTE:
When mounting in a standard threaded
fi tting, the electrode must be mounted
horizontal to 60 degrees below horizontal
position only:
0°
SAFETY INSTRUCTIONS
1. Use appropriate eye, face, hand, body
and/or respiratory protection when using
chemicals or solvents
2. Prior to installation or removal:
a. Depressurize and vent system
b. Drain below sensor level
3. Confirm chemical compatibility before use
4. Do not exceed the maximum
temperature/pressure specifications
5. Do not alter product construction
If installing into a threaded connection:
6. Inspect threads to ensure integrity. Do not
install a sensor that has damaged threads
7. Apply PTFE tape to the process connection
threads in accordance with industry
practices
8. Hand tighten the sensor into the process
connection. DO NOT USE TOOLS
Failure to follow
these instructions may
result in personal injury
See peel & stick warning label on back!
WARNING
Attach near sensor
3-2700.615 (B-04/08)
YES
275X Wet-Tap
YES
275X Wet-Tap with 2751 or 2760 and
3719 pH/ORP Wet-Tap Assembly
1) Choose sensor; 2) Choose preamplifi er or sensor electronics;
3) Choose Wet-Tap assembly; 4) Choose customer supplied
mounting option
1
Wet-Tap pH or
ORP Sensor:
3-2756-WTP
3-2756-WTP-1
3-2757-WTP
2
2760
Preamplifier:
3-2760-11
3-2760-21
OR
2751 Smart Sensor
Electronics:
3-2751-1
3-2751-2
4
-15°
YES
YES
+15°
276X
NO
NO
277X
Signet 275X, 276X, 2777X Series pH and ORP Electrodes
NO
YES
YES
0°
Horizontal
YES
YES
YES
3
3719 Wet-Tap Assembly:
3-3719-11
3-3719-12
3-3719-21
3-3719-22
4
Customer supplied Tees and Fittings
Page 5
Removing from In-Line Installation
• The use of this product assumes
that operators are trained and are
familiar with this type of device.
• They should be knowledgeable of
the potential risks associated with
pressurized piping systems.
• Operators MUST follow all
necessary safety procedures.
Submersible Installations
In-line removal Instructions:
1. Wear safety goggles or face shield during removal.
Use all appropriate eye, face, hand, body and/or respiratory
protection when working with chemicals or solvents.
3. Depressurize and vent the piping system.
3. Drain the system to below sensor level.
4. Practice proper Lock Out/ Tag Out procedures when the sensor
is removed for maintenance to prevent accidental opening and
exposure to potentially hazardous chemicals.
The user must supply the following hardware
to complete a submersible installation:
• ¾ in. Pipe, ¾ in. (DN 20) Male Adapter, Liquid Tight
Connection at top of pipe assembly
• Wiring junction box
• Pipe clamps (quick-release type recommended)
• Tank fl ange for closed tanks
• Silicone Caulking Sealant & PTFE Tape
The Signet pH/ORP electrodes
are designed to install in tanks
by attaching conduit to the ¾ in.
(
ISO 7/1-R ¾ )
threads at the top of
1
the accompanying preamplifi er or
sensor electronics:
1. The O-ring at the top of the
electrode fi ts very tightly into
the preamplifi er. Use a small
amount of non-petroleum
based lubricant to assist the
assembly.
2. To prevent moisture from
migrating into the preamplifi er,
backfi ll the conduit with 3 in. to
4 in. of sealant.
3. Mount electrodes in a location
with ample clearance to
3
3
B.
remove them for periodic
cleaning and recalibration.
4. Choose a location that keeps
the electrode glass completely
submersed at all times.
D.
C.
A.
Preamplifier
Lubricate
O-ring(s)
Technical Note:
• Mount the electrode near tank outlets, away from reagent
addition areas.
• Use the ¾ in. (
ISO 7/1-R ¾
) threads at the top of the
preamplifi er to run the cable inside pipe or conduit.
• Place the electrode tip in 3.0M KCl solution or pH 4 Bu er
for temporary storage during system maintenance to avoid
dehydration. For long term storage place the electrode tip
in 3.0M KCl solution.
Fill with
3 to 4 in.
of sealant
3/4 in. NPT or
ISO 7/1-R 3/4
Sealant
J-Box
2
Customer
supplied
pipe
B.
D.
C.
A.
4
B.
C.
A.
B.
C.
A.
E.
2 in.
min.
Open
tanks
Caution: If liquid level is not constant, always ensure liquid contact with electrode tip
Open
tanks
Signet 275X, 276X, 2777X Series pH and ORP Electrodes
Closed
tanks
Closed
tanks
E.
5
Page 6
Electrode Date Code
• The electrode date code indicates the
manufacturing date of the electrode.
• Electrodes should be put into service as
soon as possible and should not remain in
the box for more than two years.
• Over time, the storage solution (found in
the "boot" covering the electrode tip) will
evaporate or leak, allowing the delicate
sensing tip and reference junction to dry.
• To rehydrate a dry electrode, soak the tip in
3.0 mol/L KCl solution for 24 to 48 hours.
Preheating the KCl solution to <140 °F may
speed up the re-hydration process.
• Electrodes more than 2 years old may still be
functional, but will take longer to rehydrate.
• Restoration may not be e ective for severely
dehydrated electrodes.
Letter = Month
N = January
M = February
L = March
K = April
J = May
H = June
G = July
F = August
E = September
D = October
C = November
B = December
K2K2
Example: K2 = manufactured in April 2017
Numeral = Year
5 = 2010
6 = 2011
7 = 2012
8 = 2013
9 = 2014
0 = 2015
1 = 2016
2 = 2017
3 = 2018
4 = 2019
5 = 2020
6 = 2021
Electrode Care
Depending on the type of application and the accuracy needed, pH and ORP electrodes will require routine maintenance.
Contaminated/dirty electrodes should be swapped with properly cleaned conditioned and calibrated electrodes.
The solution used to clean an electrode varies depending on the type of coating:
Caution: Always wear appropriate safety gear and exercise proper safety practices when working with or near chemicals
• General Cleaning – Soak the electrode for 5 minutes in a mixture of warm tap water (< 140° F), and mild detergent such as
liquid dish detergent. A soft brush, like a toothbrush may also be used to clean o particulates.
• Biofi lm and bacterial growth – soak the electrode in a diluted household laundry bleach solution (pH electrodes only), 1part
bleach to 10 parts water for 10 minutes.
• Alkaline or Scale – Lime/calcium and mineral buildup deposits may be removed by soaking the electrode in a solution of 2% to
5% hydrochloric acid (HCl) or vinegar for no more than 5 minutes.
• Acidic contaminants – may be removed by soaking the electrode in a weak caustic (less than 2% to 5% NaOH) for a few
minutes only. Use the least harsh chemical which will remove the contaminant within 2-5 minutes of soaking without attacking
the materials of construction.
• Oily or organic coatings – Soak the probe for 5 to 10 minutes in a solution of warm tap water < 140° F, and dish detergent.
Alternatively, use an appropriate solvent (isopropyl alcohol or similar) that will not attack the materials of construction. If
required gently clean junction and/or glass with a very soft tooth brush, and follow up with brief soaking (2-5 minutes) in 2% to
5% NaOH (sodium hydroxide). In the case of pH (not ORP) a di cult organic fouling can be treated with household bleach
(4-6%) as a substitute for the dish detergent.
• ORP Platinum Coating – Gently wipe the electrode surface with a soft lint-free paper towel. If the various forms of chemical
cleaning are not su cient to achieve an accurate measurement and response time, a last resort would be to polish the platinum
surface with a 0.3-1.0 micron alumina polishing slurry to remove any stubborn coatings.
• After cleaning, rinse pH/ORP electrode in distilled or tap water, then re-examine the electrode for damage that may have been
hidden from view. Sensor may not initially behave properly; and have a temporary o set due to the cleaning chemistry. Proper
conditioning is always recommended
Electrode Conditioning
Soak sensor tip (pH or ORP) in 3 mol/L KCl (potassium chloride), for at least 45 minutes to regenerate / condition.
The more aggressive the cleaning, the longer the soak in potassium chloride.
Failure to soak the electrode will cause the electrode to drift for a time after the cleaning procedure, and could adversely a ect the
calibration process/results.
If the cleaning and conditioning yield results within operational tolerance, the pH/ORP sensor is once again suitable for use.
However, if the results do not bring the readings of the pH/ORP sensor within tolerance, it is time to replace the sensor.
6
Signet 275X, 276X, 2777X Series pH and ORP Electrodes
Page 7
pH System Calibration
There are two functions in a pH electrode that require the system to be calibrated:
Temperature Calibration
• The temperature output of the electrode (measured by a 3K Balco or Pt1000 RTD) must be calibrated only once. When a new electrode
is installed, it does not need to be repeated.
• Because the temperature measurement has a signifi cant infl uence on the electrochemical measurement, the temperature output in new
pH electrodes should always be calibrated before the pH/mV calibration.
NOTE: All Signet transmitters and controllers incorporate automatic temperature compensation.
pH error due to temperature changes in fl uid
°C pH 2 pH 3 pH 4 pH 5 pH 6 pH 7 pH 8 pH 9 pH 10 pH 11 pH 12
0.15 0.12 0.09 **0.06 0.03 0 0.03 0.06 0.09 0.12 0.15
15
25
35
45
Table 1
As the pH value moves away from neutral (7 pH) or the temperature moves away from 25 ºC, the electrochemical output is a ected.
* Example: At pH 5 the mV output of the electrode is not a ected if the temperature is at 25 °C.
** The electrode output will be shifted by 0.06 pH units if the temperature is reduced to 15 °C.
55
Off set and Slope Calibration
The pH electrode calibration is an important function that must be done routinely to standardize the electrode due to its ever-changing
characteristics. The electrode contains a gel that depleates over time, so the instrument must be readjusted periodically to maintain
system accuracy. There are many infl uences, including aging, temperature, coatings and chemicals used that will a ect the probe
characteristics. After cleaning and conditioning, Signet pH electrodes may be calibrated in two pH bu er solutions of di erent pH
values (a two point calibration).
000* 0 0000000
0.15 0.12 0.09 0.06 0.03 0 0.03 0.06 0.09 0.12 0.15
0.3 0.24 0.18 0.12 0.06 0 0.06 0.12 0.18 0.24 0.3
0.45 0.36 0.27 0.18 0.09 0 0.09 0.18 0.27 0.36 0.45
The pH electrode is calibrated by placing it in a bu er solution of known pH and measuring the cell potential.
This is a linear function of pH in the range of pH 2-11, therefore two calibration points are needed. Most
common calibration bu ers are pH 4.01 and pH 7.00 (@ 25 °C). If the pH measurements are made in an acid
to neutral range, we recommend using bu er pH 4.01 and bu er pH 7.00 for calibration. If an alkaline sample
is measured, we recommend using bu er 7.00 and bu er 10.01 for calibration.
The response of the glass electrode is characterized by two parameters, o set and slope. The theoretical
output of a pH electrode at pH 7 is 0 mV. The o set, or zero pH is the deviation of the pH from the nominal
value. In the Signet transmitters, the o set calibration is performed under STANDARD.
The glass electrode slope is the mV developed per each pH unit (mV/pH). At 25 °C, the theoretical slope is
59.16 mV/pH. So, at pH 4.01, +177 mV will be generated, while at pH 10.01 (with a lower H+ concentration),
a potential of -177 mV will be generated, (see Table 2). A new electrode however, will generate 0 ± 15 mV
in pH 7.00 and will have a slope e ciency between 93.2 and 103%. In the Signet transmitters, manual slope
calibration is performed under SLOPE.
Theoretical mV
Values @ 25 °C
pH mV
2 +295.8
3 +236.64
4 +177.48
5 +118.32
6 +59.16
70
8 –59.16
9 –118.32
10 –177.48
11 –236.64
12 –295.8
Table 2
Signet 275X, 276X, 2777X Series pH and ORP Electrodes
7
Page 8
pH System Calibration cont.
How to calculate a pH electrode slope effi ciency
Two pH bu ers are selected to check the pH probe performance, pH 4.01 and pH 7.00. The ratio of the measured potentials (E2-E1) to
the di erence of pH (7.00 – 4.01) gives the slope of the straight line.
1. Read the mV potential generated by the electrode in two calibration bu ers
2. Determine the slope (the mV potential generated per pH unit)
3. Divide this number by the theoretical slope, 59.16 mV/pH @ 25 °C and multiply by 100.
Example 1
pH electrode generates -12 mV in pH 7.00 bu er
and +162 mV in pH 4.01 bu er.
160 mV - (-12 mV) = 172 mV
172 mV/ 3 = 57.33 mV/pH unit
57.33/59.16 x 100 = 96.9 % slope e ciency
Example 2
pH electrode generates -45 mV in pH 7.00 bu er
and +115 mV in pH 4.01 bu er.
115 mV - (-45 mV) = 160 mV
160 mV/3 = 53.33 mV/pH unit
53.33/59.16 x 100 = 90.1%
In Example 2, slope e ciency of 90.1% is acceptable but the o set of -45 mV is not.
An o set shift can be the result of the reference electrode being contaminated or poisoned.
A slope shift can be the result of the glass being etched or coated with a hard build-up.
As the electrode ages, the slope decreases gradually, generally a slope between 85% and 105% is acceptable. If the o set value
(pH 7.00) is > +/- 45 mV, electrode should be replaced. When a great accuracy is required from the electrode, the o set and the slope
values need to be as close as possible to the theoretical values.
Refer to the Calibration Procedure section of the instrument manual for a 2 point pH calibration. If the sensor is used in a 4 to 20 mA
‘blind application’ refer to the Calibration section of the 2751 Smart Sensor Electronics for a 2-point EasyCal pH calibration.
ORP System Calibration
ORP electrodes do not incorporate a temperature sensor, so the only system calibration required is the electrochemical adjustment.
ORP electrodes should need less frequent calibration than a typical pH sensor, the redox potential is a characteristic of the interaction
between the platinum measuring electrode and the redox species in solution.
ORP measurement is only an indicator of the process solution reducing or oxidizing potential. Always perform a single point calibration
(standardization). Using the 9900 or 9950 transmitter, this can be performed under STANDARD. Disregard the SLOPE calibration.
If calibrating the ORP electrode under EasyCal (9900 Transmitters, Gen IV or later), one point calibration will be your only option.
A new ORP electrode measures the listed value +/- 20 mV. A two-point calibration will not increase the accuracy of the measurement
given the +/- 20 mV repeatability of the sensor itself. On top of that, the ORP is not temperature compensated, so if the measurement
is not done at 25 °C, any benefi t gained will be lost. A true two-point calibration is possible in very few applications where only one
redox couple is present in solution and its chemistry is known.
Calibration should be done using ORP premade standard solutions such as Zobell's solution and Light's solution, or solutions made
using the standard pH 4.01 bu er and pH 7.00 bu er with quinhydrone powder mixed in until saturation is reached (Table 3). If all the
quinhydrone does dissolve, continue to add small amounts and stir until a small amount of quinhydrone remains un-dissolved after
mixing. Quinhydrone is the oxidizer that is measured by the ORP electrode. Please note that Zobell's solution is not compatible with
the AutoCal function in Signet ORP instrumentation.
Pre-packaged or mixed Quinhydrone solutions are strong and may have a long lasting e ect on the electrode, therefore after
calibration it's recommended to properly condition the electrode before returning to the process. It is also possible to calibrate the ORP
electronics based upon a known grab sample confi rmed with a lab meter.
Pick a solution with a mV value closest to the process value and if possible adjust the temperature of the solution to the process
temperature to minimize the o set.
The ORP electrode is functional until the o set exceeds 50 mV.
When the o set measures greater than 50 mV, the electrode should
replaced.
Table 3:
ORP test solutions
*Saturate 50 mL of pH 4 or
pH 7 bu er with 1/8 g quinhydrone
Zobell's
solution
ORP at 20 °C 268 mV 92 mV
ORP at 25 °C 228 mV 469 mV 263 mV 86 mV
ORP at 30 °C 258 mV 79 mV
Light's
solution
4 pH buff er
w/quinhydrone*
7 pH buff er
w/quinhydrone*
8
Signet 275X, 276X, 2777X Series pH and ORP Electrodes
Page 9
Buff er Solutions
Proper handling, storage and use of bu ers is very important on the pH and ORP measurement accuracy. If the bu ers are
contaminated or used improperly, the calibration will be inaccurate and all subsequent measurements will be wrong.
• When calibrating pH electrodes, always use pH bu ers in the range of your sample.
• To achieve an accurate calibration make sure the electrode and the bu er are at the same temperature.
• Bu ers have limited shelf life. Do not use a bu er if the expiration date has passed.
• Never return used bu ers to the bu er bottle. Discard it.
• Do not leave the bu er bottle open (exposed to air).
The atmospheric carbon dioxide lowers the pH of the alkaline bu ers (10.01 pH).
• To avoid contamination, rinse the electrode with distilled or tap water before placing it in the bu er. If necessary, the electrode
might be blotted dry using a lint-free paper towel (e.g. Kimwipes) to remove excess water. Be extra careful not to touch or rub
the surface of the glass. The wiping of the glass can produce a static charge that will interfere with the voltage reading of the
electrode. In addition to this, the hydration gel layer is interrupted.
• Store bu ers at room temperature.
• Signet o ers the following pH bu er solutions, pH 4.01, pH 7.00 and pH 10.01.
• Make fresh bu er solutions just before using. ORP solutions made with quinhydrone are very unstable and may not read
properly after being exposed to air for a prolonged time. These solutions must be discarded after a few hours.
• Dispose of all calibration solutions in accordance with local guidelines and regulations.
Electrode Storage
Proper electrode storage maximizes electrode performance and extends electrode life.
Prior to storage - add 3 mol/L KCl to the electrode storage cap (about half full), and carefully secure the cap onto the electrode tip.
• Store boxed electrodes wet, fl at or upright (electrode tip down) to maximize hydration of the glass surface.
• Store electrodes in stable temperature environment, avoiding freezing conditions (below 0 °C (<33° F) and heat above 100° F).
• Never store the electrode in deionized (DI) water. Use 3 mol/L KCl solution to keep the glass wet when out of the process.
Short term storage (up to 24 hours) - soak the electrode tip in either pH 4.01 bu er or 3 mol/L KCl solution.
• Drying out of the pH sensitive glass and the junction must be avoided (or damage to the electrode will occur).
• Prior to electrode installation, make sure there’s a light fi lm of synthetic grease (such as silicone-free grease) applied to the upper
electrode O-ring. If the electrode will be installed into a GF Signet Installation Fitting, then also apply a thin fi lm of synthetic
grease to the lower O-ring.
Long term storage (longer than 24 hrs) - add 3 mol/L KCl solution to the storage cap (about half full) and carefully secure the cap onto
the electrode tip. This will ensure probes are always ready to use.
Signet 275X, 276X, 2777X Series pH and ORP Electrodes
9
Page 10
Response Time/Stability
Response time and stability are a ected by the condition of the pH glass measuring surface (for an ORP electrode, the platinum
surface),the reference junction and the reference solution. Electrodes may sometimes be restored to acceptable levels by cleaning the
measuring surface and reference junction.
Electrode mV values should remain stable ± 3 mV. Conditions that may cause fl uctuations are:
• Electrode coating
• Clogged reference junction
• Ground fault: If proper operation is observed in the beaker, but readings are unstable in the application, a ground fault may exist.
• Using instrumentation with isolated inputs and outputs may restore stable operation.
• Solution grounding may also restore stable operation.
Maintenance and Cleaning
276X Series Diff erential Electrodes
Di erential electrodes have a replaceable salt bridge and the
electrolyte chamber can be refi lled. The electrolyte chamber
should be full. If any fl uid is audible when shaken, the chamber
should be refi lled. Refi ll the electrolyte chamber when the
electrode o set exceeds 40-45 mV. Replace the salt bridge
when performance becomes sluggish or if the output is erratic
or inaccurate.
Replacing the Salt Bridge
Parts Required: Salt Bridge (order number 3864-0001) and
Di erential Reference Solution
(order number 3864-0002)
Tools Required: Small pliers
Procedure:
1. Remove sensor from mounting.
2. Hold upside down and unscrew salt bridge using a pair of
small pliers. Be careful not to damage the glass bulb!
3. Drain the depleted reference solution and dispose of
properly.
4. Fill reference chamber with fresh reference solution
(approx. 30 ml).
5. Replace salt bridge and screw fi nger tight. Solution will drip
out while screwing in salt bridge.
Use pliers to turn approximately ¼ turn past fi nger-tight.
6. Perform calibration (standard and slope) before returning
the system to service.
NOTE:
The refi llable electrolyte chamber in 276X series
di erential electrodes may leak during storage and
shipping. Check the fl uid and refi ll before installation
if necessary.
WARNING!
Wear appropriate eye, face, hand, body, and
respiratory protection when using chemicals or
solvents.
10
Signet 275X, 276X, 2777X Series pH and ORP Electrodes
Page 11
Ordering Information
Mfr. Part No. Code Description
Signet 275X Series Wet-Tap DryLoc pH and ORP Electrodes
pH Electrode
3-2756-WTP 159 001 390 Bulb pH electrode, plastic body, DryLoc connector, use with the 3719 Wet-Tap Assembly only,
Pt1000 RTD for connection to the 8900, 9900 and 9950 instruments when used with the 2751 Smart
Sensor Electronics
3-2756-WTP-1 159 001 384 Bulb pH electrode, plastic body, DryLoc connector, use with the 3719 Wet-Tap Assembly only, 3 K
Balco RTD
ORP Electrode
3-2757-WTP 159 001 391 ORP electrode, plastic body, DryLoc connector, use with the 3719 Wet-Tap Assembly only, to use with
2751 Smart Sensor Electronics or 2760 Preamplifi er
Signet 276X Series Diff erential DryLoc pH and ORP Electrodes
pH Electrode
3-2764-1 159 000 943 Flat surface pH di erential electrode, DryLoc connector, 3 K Balco RTD
3-2764-2 159 000 944 Flat surface pH di erential electrode, DryLoc connector, Pt1000 RTD for connection to 8900, 9900 and
9950 instruments when used with the 2751 Smart Sensor Electronics
3-2766-1 159 000 949 Bulb pH di erential electrode with bulb protection, DryLoc connector, 3 K Balco RTD
3-2766-2 159 000 950 Bulb pH di erential electrode with bulb protection, DryLoc connector, Pt1000 RTD for connection to
8900, 9900 and 9950 instruments when used with the 2751 Smart Sensor Electronics
ORP Electrode
3-2765-1 159 000 946 Flat surface ORP di erential electrode, DryLoc connector, 10 K ID resistor for connection to 8900,
9900 or 9950 when used with the 2751 Smart Sensor Electronics
3-2767-1 159 000 952 Bulb ORP di erential electrode with bulb protection, DryLoc connector, 10 K ID resistor for connection
to 8900, 9900 or 9950 when used with the 2751 Smart Sensor Electronics
Signet 277X Series Threaded DryLoc pH and ORP Electrodes
pH Electrode
3-2774 159 000 955 Flat surface pH electrode, DryLoc connector, 3 K Balco RTD
3-2774-1 159 000 956 Flat surface pH electrode, DryLoc connector, Pt1000 RTD for connection to 8900, 9900 and 9950
instruments when used with the 2751 Smart Sensor Electronics
3-2774-HT 159 001 796
3-2774-HT-C 159 001 795
3-2774-HT-ISO 159 001 794
3-2776 159 000 959 Bulb pH electrode with bulb protection, DryLoc connector, 3 K Balco RTD
3-2776-1 159 000 960 Bulb pH electrode with bulb protection, DryLoc connector, Pt1000 RTD for connection to 8900, 9900 and
Signet 277X Series Threaded DryLoc pH and ORP Electrodes
ORP Electrodes
3-2775 159 000 957 Flat surface ORP electrode, DryLoc connector, 10 K ID resistor for connection to the 8900, 9900 or 9950
3-2777 159 000 961 Bulb ORP electrode with bulb protection, DryLoc connector, 10 K ID resistor for connection to the 8900,
Flat surface pH electrode, DryLoc connector, 3K Balco RTD, High Temperature (110 °C, 230 °F)
in-line install only.
Flat surface pH electrode, DryLoc connector, BNC connector, 3K Balco RTD, NPT, High Temperature
(110 °C, 230 °F), NPT, 15 ft cable, no memory chip, for submersible installations, can only be connected
to the 2751 or 2760 sensor electronics if used with the 3-2722 BNC adapter.
Flat surface pH electrode, DryLoc connector, 3 K Balco RTD, High Temperature (110 °C, 230 °F),
3/4" ISO, 3K Balco RTD, in-line install only.
9950 instruments when used with the 2751 Smart Sensor Electronics
when used with the 2751 Smart Sensor Electronics
9900 or 9950 when used with the 2751 Smart Sensor Electronics
,
Signet 275X, 276X, 2777X Series pH and ORP Electrodes
11
Page 12
Ordering Information cont.
Special Order Options - Please consult the factory
Mfr. Part No. Code Description
Electrode
3-2774-HF Special Order Flat glass pH electrode for hydrofl uoric acid applications <2%, DryLoc connector, in-line sensor, NPT
3-2775-HT Special Order Flat surface ORP electrode, high temperature (110 °C, 230 °F), DryLoc connector, ¾" NPT,
3K RTD, in-line install only
3-2775-AU Special Order Flat surface ORP electrode, gold measuring electrode, DryLoc connector, NPT, in-line sensor
3-2776-HT Special Order Bulb glass pH electrode with protection, high temperature (110 °C, 230 °F), DryLoc connector,
¾" NPT, 3K RTD, in-line install only
3-2776-HF Special Order Bulb glass pH electrode with protection, hydrofl uoric acid applications <2%, DryLoc connector,
in-line sensor, NPT
3-2777-HT Special Order Bulb ORP electrode with protection, high temperature (110 °C, 230 °F), DryLoc connector, ¾" NPT,
3K TRD, in-line install only
3-2777-AU Special Order Bulb ORP electrode with protection, gold measuring electrode, DryLoc connector, in-line sensor, NPT
Special Order Options- Please consult the factory
Accessories and Replacement Parts for all pH
Mfr. Part No. Code Description
Calibration
3-2759 159 000 762 pH/ORP System Tester
3-2759.391 159 000 764 Adapter Cable for use with 2751, 2760
3-0700.390 198 864 403 pH Bu er Kit (includes 4.0, 7.0, and 10.0 bu er powder)
3-2700.395 159 001 605 Calibration Kit: includes 3 PP cups, cups stand, 1 pint pH 4.01, 1 pint pH 7.00
3822-7115 157 001 606 20 g bottle Quinhydrone for ORP calibration (must use pH 4.01 and/or pH 7.00 bu er solutions)
3822-7004 159 001 581 pH 4 bu er solution, 1 pint (473 ml) bottle
3822-7007 159 001 582 pH 7 bu er solution, 1 pint (473 ml) bottle
3822-7010 159 001 583 pH 10 bu er solution, 1 pint (473 ml) bottle
3800-5000 159 838 107 3.0M KCl storage solution for pH and ORP, 1 pint (473 ml) bottle
3-2700.398 159 001 886 O-ring lubricant kit (5 packs of Super Lube, 1cc each)
Accessories and Replacement Parts for 275X
1224-0205 159 000 836 O-ring, EPR (EPDM)
Accessories and Replacement Parts for 276X
3864-0001 159 001 007 Replacement salt bridge (2764-2767)
3864-0002 159 001 008 Replacement reference electrolyte solution, 500 ml
2120-0015 159 001 009 CPVC adapter: 1½ in. to 1 in.
2122-0015 159 001 010 PVDF adapter: 1½ in. to 1 in.
Georg Fischer Signet, LLC, 3401 Aerojet Avenue, El Monte, CA 91731-2882 U.S.A. • Tel. (626) 571-2770 • Fax (626) 573-2057
For Worldwide Sales and Service, visit our website: www.gfsignet.com • Or call (in the U.S.): (800) 854-4090
For the most up-to-date information, please refer to our website at www.gfsignet.com
3-2764.090 Rev 12 12/19 English © Georg Fischer Signet LLC 2019
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