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GF Signet 276 Differential Series Operating Instructions Manual

Signet 277 Threaded Series\ Signet 275 Wet-Tap Series

Made by: GF
Type: Operating Instructions
Category: Measuring Instruments
Pages: 12
Size: 1.30 MB


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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

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


 connector with gold-plated contacts, designed specifi cally for use 

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 off 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 KΩ 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.

The Signet 276X Series Diff 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 Diff 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, KNO


 in the front chamber (to block 

various poisoning ions such as copper (Cu


), lead (Pb


), mercury (Hg


)) 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



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 KΩ, 
or Pt1000 RTD.



Rev 9  11/18 











Operating Instructions

Cancer and Reproductive Harm 


California Prop. 65



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Signet 275X, 276X, 2777X Series pH and ORP Electrodes

Refer to your local Georg Fischer Sales offi  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 offi  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 buff 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, chemical poisoning, dry-out) or 

mishandling (e.g. broken glass, damaged membrane, freezing 

and/or extreme temperatures).

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 



Service and Support

 click on 

Product Registration Form

  •  If this is a pdf manual (digital copy), 

click here

Warranty Information

Product Registration

Safety Information

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.



 the sensor into the process connection.




45 mm 

(1.8 in.) 

43 mm 

(1.7 in.) 

121 mm 

(5.27 in.) 

1 in. 

¾ in. 

¾ in. 


32 mm 

(1.3 in.) 

276X Series

277X Series
Bulb Electrode

277X Series
Flat Electrode

218 mm 

(8.57 in.) 

35 mm 

(1.4 in.) 

11.9 mm 
(0.47 in.) 

2756 Wet-Tap pH
2757 Wet-Tap ORP

Lubricate o-rings with a 
non-petroleum based, 
viscous lubricant (grease) 
compatible with the 


Caution / Warning / Danger

Indicates a potential hazard. 
Failure to follow all warnings may lead to equipment damage, injury, or 

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 

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.

Chemical Compatibility


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Signet 275X, 276X, 2777X Series pH and ORP Electrodes

40 50 60 70 


90 100 










10 20 30 

32 122 




50 86 

277X Series

0 °C to 85 °C @ 6.89 bar

(32 °F to 185 °F @ 100 psi)

pH/ORP Electrodes
276X Series and 277X Series
Pressure vs. Temperature

276X Series ONL




 is a registered trademark of Chevron Phillips Chemical

Specifi cations

276X Series Diff erential Electrodes
277X Series Threaded Electrodes

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  ......................... Buff ered KNO



277X Series  ......................... KCI/AgCl gel with KNO



Reference Element

276X Series .......................... pH glass electrode
277X Series .......................... Ag/AgCl

Temperature Sensor

276X Series pH .................... 3 KΩ or Pt1000 RTD
277X Series pH .................... 3 KΩ or Pt1000 RTD
276X Series ORP ................. 10 KΩ ID for Signet instruments;
277X Series ORP ................. 10 KΩ ID for Signet instruments

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

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 KΩ Balco
ORP Identifi cation ................. 10 KΩ 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


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)

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.


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Signet 275X, 276X, 2777X Series pH and ORP Electrodes

In-Line Installation

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

See peel & stick warning label on back! 

Attach near sensor

3-2700.615  (B-04/08)

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 
8.   Hand tighten the sensor into the process     
      connection.             DO NOT USE TOOLS   

Failure to follow

these instructions may

result in personal injury



1.  2774 and 2775 electrodes can be mounted at any angle
2.  Diff 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. 



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.


When mounting in a standard threaded 
fi tting, the electrode must be mounted 
horizontal to 60 degrees below horizontal 
position only:




















Customer supplied Tees and Fittings

3719 Wet-Tap Assembly:

Wet-Tap pH or
ORP Sensor:



2751 Smart Sensor



275X Wet-Tap


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Signet 275X, 276X, 2777X Series pH and ORP Electrodes









Fill with

3 to 4 in.

of sealant



3/4 in. NPT or
ISO 7/1-R 3/4










Caution: If liquid level is not constant, always ensure liquid contact with electrode tip

2 in. 















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 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.

Removing from In-Line Installation

Submersible Installations

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 Buff er 

for temporary storage during system maintenance to avoid 
dehydration. For long term storage place the electrode tip 
in 3.0M KCl solution.

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 
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 

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 
remove them for periodic 
cleaning and recalibration.

4.  Choose a location that keeps 

the electrode glass completely 
submersed at all times.


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Signet 275X, 276X, 2777X Series pH and ORP Electrodes

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:


 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 off  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 diffi  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 suffi  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 off 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 aff 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.


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 eff ective for severely 
dehydrated electrodes.

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

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

Example: K2 = manufactured in April 2017

Electrode Date Code




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Signet 275X, 276X, 2777X Series pH and ORP Electrodes

There are two functions in a pH electrode that require the system to be calibrated:

Temperature Calibration

As the pH value moves away from neutral (7 pH) or the temperature moves away from 25 ºC, the electrochemical output is aff ected.


  Example:  At pH 5 the mV output of the electrode is not aff 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.

•  The temperature output of the electrode (measured by a 3KΩ 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.



  All Signet transmitters and controllers incorporate automatic temperature compensation.

pH error due to temperature changes in fl uid


pH 2

pH 3

pH 4

pH 5

pH 6

pH 7

pH 8

pH 9

pH 10

pH 11

pH 12

















* 0












































Table 1

pH System Calibration

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 aff ect the probe 
characteristics. After cleaning and conditioning, Signet pH electrodes may be calibrated in two pH buff er solutions of diff erent pH 
values (a two point calibration). 

The pH electrode is calibrated by placing it in a buff 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 buff 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 buff er pH 4.01 and buff er pH 7.00 for calibration.  If an alkaline sample 
is measured, we recommend using buff er 7.00 and buff er 10.01 for calibration. 

The response of the glass electrode is characterized by two parameters, off set and slope.  The theoretical 
output of a pH electrode at pH 7 is 0 mV.  The off set, or zero pH is the deviation of the pH from the nominal 
value.  In the Signet transmitters, the off 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 effi  ciency between 93.2 and 103%. In the Signet transmitters, manual slope 
calibration is performed under SLOPE.

Theoretical mV 
Values @ 25 °C

























Table 2


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Signet 275X, 276X, 2777X Series pH and ORP Electrodes

pH System Calibration cont.

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 buff er and pH 7.00 buff 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 eff 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 off set.

The ORP electrode is functional until the off set exceeds 50 mV. 
When the off set measures greater than 50 mV, the electrode should 

ORP electrodes do not incorporate a temperature sensor, so the only system calibration required is the electrochemical adjustment.





4 pH buff er


7 pH buff er


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

*Saturate 50 mL of pH 4 or 

pH 7 buff er with 1/8 g quinhydrone

Table 3:

ORP test solutions

ORP System Calibration

How to calculate a pH electrode slope effi


Two pH buff 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 diff erence of pH (7.00 – 4.01) gives the slope of the straight line.


Read the mV potential generated by the electrode in two calibration buff ers


Determine the slope (the mV potential generated per pH unit)


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 buff er 
and +162 mV in pH 4.01 buff er. 

160 mV  - (-12 mV) = 172 mV
172 mV/ 3 = 57.33 mV/pH unit
57.33/59.16 x 100  = 96.9 % slope effi  ciency

In Example 2, slope effi  ciency of 90.1% is acceptable but the off set of -45 mV is not. 
An off 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 off set value 
(pH 7.00) is > +/- 45 mV, electrode should be replaced. When a great accuracy is required from the electrode, the off 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.

Example 2

pH electrode generates -45 mV in pH 7.00 buff er 
and +115 mV in pH 4.01 buff er.

115 mV - (-45 mV) = 160 mV
160 mV/3 = 53.33 mV/pH unit
53.33/59.16 x 100 = 90.1%


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Signet 275X, 276X, 2777X Series pH and ORP Electrodes

Buff er Solutions

Proper handling, storage and use of buff ers is very important on the pH and ORP measurement accuracy. If the buff 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 buff ers in the range of your sample. 


To achieve an accurate calibration make sure the electrode and the buff er are at the same temperature.


Buff ers have limited shelf life.  Do not use a buff er if the expiration date has passed. 


Never return used buff ers to the buff er bottle.  Discard it. 


Do not leave the buff er bottle open (exposed to air).  
The atmospheric carbon dioxide lowers the pH of the alkaline buff ers (10.01 pH).


To avoid contamination, rinse the electrode with distilled or tap water before placing it in the buff 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 buff ers at room temperature. 


Signet off ers the following pH buff er solutions, pH 4.01, pH 7.00 and pH 10.01.


Make fresh buff 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 buff 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.


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Signet 275X, 276X, 2777X Series pH and ORP Electrodes

276X Series Diff erential Electrodes

Diff 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 off 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  


Diff erential Reference Solution



(order number 3864-0002)

Tools Required:  Small pliers

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 


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.


The refi llable electrolyte chamber in 276X series 
diff erential electrodes may leak during storage and 
shipping. Check the fl uid and refi ll before installation 
if necessary.

Maintenance and Cleaning



 Wear appropriate eye, face, hand, body, and 
respiratory protection when using chemicals or 

Response time and stability are aff 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.

Response Time/Stability


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Signet 275X, 276X, 2777X Series pH and ORP Electrodes

Ordering Information

Mfr. Part No.



Signet 275X Series Wet-Tap DryLoc pH and ORP Electrodes
pH Electrode


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


159 001 384 Bulb pH electrode, plastic body, DryLoc connector, use with the 3719 Wet-Tap Assembly only, 3 KΩ 

Balco RTD

ORP Electrode


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


159 000 943 Flat surface pH diff erential electrode, DryLoc connector, 3 KΩ Balco RTD


159 000 944 Flat surface pH diff erential electrode, DryLoc connector, Pt1000 RTD for connection to 8900, 9900 and 

9950 instruments when used with the 2751 Smart Sensor Electronics 


159 000 949 Bulb pH diff erential electrode with bulb protection, DryLoc connector, 3 KΩ Balco RTD


159 000 950 Bulb pH diff 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


159 000 946 Flat surface ORP diff erential electrode, DryLoc connector, 10 KΩ ID resistor for connection to 8900, 

9900 or 9950 when used with the 2751 Smart Sensor Electronics 


159 000 952 Bulb ORP diff erential electrode with bulb protection, DryLoc connector, 10 KΩ 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


159 000 955 Flat surface pH electrode, DryLoc connector, 3 KΩ Balco RTD


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 


159 001 796

Flat surface pH electrode, DryLoc connector, 3KΩ Balco RTD, High Temperature (110 °C, 230 °F)



in-line install only



159 001 795

Flat surface pH electrode, DryLoc connector, BNC connector, 3KΩ 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.


159 001 794

Flat surface pH electrode, DryLoc connector, 3 KΩ Balco RTD, High Temperature (110 °C, 230 °F),
3/4" ISO, 3KΩ Balco RTD, in-line install only.


159 000 959 Bulb pH electrode with bulb protection, DryLoc connector, 3 KΩ Balco RTD


159 000 960 Bulb pH electrode with bulb protection, DryLoc connector, Pt1000 RTD for connection to 8900, 9900 and 

9950 instruments when used with the 2751 Smart Sensor Electronics 

Signet 277X Series Threaded DryLoc pH and ORP Electrodes
ORP Electrodes


159 000 957 Flat surface ORP electrode, DryLoc connector, 10 KΩ ID resistor for connection to the 8900, 9900 or 9950 

when used with the 2751 Smart Sensor Electronics 


159 000 961 Bulb ORP electrode with bulb protection, DryLoc connector, 10 KΩ ID resistor for connection to the 8900, 

9900 or 9950 when used with the 2751 Smart Sensor Electronics 


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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 9  11/18  English 

 © Georg Fischer Signet LLC 2018

Accessories and Replacement Parts for all pH
Mfr. Part No.





159 000 762

pH/ORP System Tester


159 000 764

Adapter Cable for use with 2751, 2760


198 864 403

pH Buff er Kit (includes 4.0, 7.0, and 10.0 buff er powder)


159 001 605

Calibration Kit: includes 3 PP cups, cups stand, 1 pint pH 4.01, 1 pint pH 7.00


157 001 606

20 g bottle Quinhydrone for ORP calibration (must use pH 4.01 and/or pH 7.00 buff er solutions)


159 001 581

pH 4 buff er solution, 1 pint (473 ml) bottle


159 001 582

pH 7 buff er solution, 1 pint (473 ml) bottle


159 001 583

pH 10 buff er solution, 1 pint (473 ml) bottle


159 838 107

3.0M KCl storage solution for pH and ORP, 1 pint (473 ml) bottle

Accessories and Replacement Parts for 275X


159 000 836

O-ring, EPR (EPDM)

Accessories and Replacement Parts for 276X


159 001 007

Replacement salt bridge (2764-2767)


159 001 008

Replacement reference electrolyte solution, 500 ml


159 001 009

CPVC adapter: 1½ in. to 1 in. 


159 001 010

PVDF adapter: 1½ in. to 1 in.

Ordering Information cont.

Special Order Options - Please consult the factory
Mfr. Part No.





Special Order

Flat glass pH electrode for hydrofl uoric acid applications <2%, DryLoc connector, in-line sensor, NPT


Special Order

Flat surface ORP electrode, high temperature (110 °C, 230 °F), DryLoc connector, ¾" NPT,
3KΩ RTD, in-line install only


Special Order

Flat surface ORP electrode, gold measuring electrode, DryLoc connector, NPT, in-line sensor


Special Order

Bulb glass pH electrode with protection, high temperature (110 °C, 230 °F), DryLoc connector,
¾" NPT, 3KΩ RTD, in-line install only


Special Order

Bulb glass pH electrode with protection, hydrofl uoric acid applications <2%, DryLoc connector, 
in-line sensor, NPT


Special Order

Bulb ORP electrode with protection, high temperature (110 °C, 230 °F), DryLoc connector, ¾" NPT,
3KΩ TRD, in-line install only


Special Order

Bulb ORP electrode with protection, gold measuring electrode, DryLoc connector, in-line sensor, NPT

Special Order Options- Please consult the factory