Industrial Electrodes

Where IndSen Electrodes Are Used

Compared with laboratory measurement, inline process monitoring places significantly higher demands on stability, reliability, and service life. These six areas cover the majority of inquiries.

• Water treatment: drinking water, cooling water, neutralization, pure water with low ionic strength, and measurements at low temperatures down to -30 °C.
• Wastewater: municipal and industrial wastewater, hydrofluoric-acid-containing wastewater, heavy metal precipitation, and sludge dewatering.
• Chemical industry: chemical production, electroplating, chlor-alkali industry, dyes, petroleum refining, pulp and paper, flue gas neutralization, and desulfurization.
• Pharma and biotechnology: biopharmaceuticals in upstream and downstream processes as well as chemical pharmaceuticals, with in-situ sterilization and autoclaving up to 140 °C.
• Food and beverages: beverages and alcohol, dairy products, yogurt and cheese, sugar and starch, yeast, and cleaning in place.
• Environment: continuous pH measurement in surface water and industrial wastewater, also with a rugged PPS housing.

Four Components Determine Whether the Measurement Holds Up in the Process

Glass membrane, diaphragm, reference system, and reference electrolyte are combined individually for each application in IndSen electrodes. Choosing these four components correctly saves maintenance and downtime later on.

Types of Glass Membrane

The pH-sensitive glass membrane detects the H⁺ activity in the solution. Glass formulation and membrane shape are among the core technologies of the pH electrode. IndSen membranes are produced on a glass lathe with reinforced walls and are 10 times more stable than those in standard pH sensors.

Membrane	Property	Typical Application
HA	Minimal alkaline error	High pH values and high temperatures
L	Lowest possible impedance	Solutions with low ionic strength or low temperature
HF	Hydrofluoric-acid resistant	Hydrofluoric-acid-containing solutions
PHY	Most stable membrane, temperature and chemical resistant	Sterilization and autoclaving

Available shapes are spherical, hemispherical, cylindrical, flat, olive, and pointed. Cylindrical and olive-shaped membranes increase the surface area and lower the impedance, while flat and pointed shapes meet special installation requirements.

Diaphragm Types

Type	Behavior	Suitable For
Ceramic	Porous ceramic material, low electrolyte outflow, prone to fouling and clogging	Water treatment, wastewater treatment plants, industrial processes
Open junction	Solid polymer electrolyte in direct contact with the sample, clog-free and maintenance-free	Heavily contaminated media such as paints, oils, and suspensions
PTFE ring	Porous PTFE ring, water-repellent, resistant to corrosion and high temperatures	Heavily contaminated, adhesive, or oily media

Reference Systems

• Long-life reference system: the reference electrolyte contains no silver ions. This prevents the reaction with sulfides or proteins in the sample that would clog the diaphragm.
• Ag⁺ trap: binds escaping silver ions and keeps the reference electrolyte free of Ag⁺. Sulfide- and amino-acid-containing samples can no longer poison the reference system.
• Long diffusion path: a long diffusion path and a non-flowing second reference medium significantly delay the diffusion of contaminants and keep the reference potential stable.

Reference Electrolytes

• Polymer electrolyte with open junction: direct sample contact, pressure-resistant up to 6 bar, suitable for nearly all measuring tasks including oily, protein-containing, and low-ionic samples as well as suspensions.
• Pre-pressurized gel: the internal pressure continuously releases small amounts of electrolyte, cleaning the diaphragm. In the Swiss patented process, the internal pressure pushes the gel into a glass capillary, allowing the pressure value to be read from outside.
• Electrolyte with salt reserve: in low-conductivity media, a standard gel-filled electrode drifts by about 15 mV per week. With a salt reserve, it’s about 0.4 mV per week.

Inline pH Electrodes at a Glance

All series are available with the cable connections Cab, S3, S8, P8, and VP; the process connection is PG13.5, and the version with a silicone cap has no process connection. Available temperature sensors are Pt1000, Pt100, and NTC.

IndSen 912 and 931, for Surface Water and Wastewater

For surface water, wastewater, and strongly alkaline solutions. The double diaphragm of the 912 prevents fouling, while the 931 works with an open junction and polymer electrolyte with no fouling risk. Both use the alkali-resistant HA membrane.

Feature	IndSen 912	IndSen 931
pH range	0 to 14 pH
Temperature	0 to 100 °C	0 to 80 °C
Pressure	6 bar
Reference system	Long-life reference	Ag+ trap
Diaphragm	Ceramic ×1	Open ×2
Electrolyte	Gel II with second diaphragm	Polymer I
Membrane	HA
Shaft	120 mm × 12 mm, lead-free glass
Example models	IndSen 912-Cab/3, IndSen 912-S8, IndSen 931-Cab/3, IndSen 931-MP4-Pt1000

IndSen 915, 925, 917, and 919, for Pure Water and Low Temperatures

For low temperatures, solutions with low ionic strength, and pure water. The L glass membrane with very low impedance delivers stable readings even where standard membranes drift. Thanks to Gel III, the 917 does not freeze at -30 °C.

Feature	IndSen 915	IndSen 925	IndSen 917	IndSen 919
pH range	0 to 11 pH
Temperature	-5 to 80 °C	-5 to 80 °C	-30 to 80 °C	-5 to 80 °C
Pressure	6 bar	6 bar	6 bar	10 bar
Reference system	Long-life	Long-life	Long-life	Ag+ trap
Diaphragm	Ceramic ×3	PTFE ring	Ceramic ×1	Ceramic ×1
Electrolyte	Gel with second diaphragm	Gel, second diaphragm, and salt reserve	Gel with second diaphragm	Pre-pressurized Gel III
Membrane	L, impedance 50 MΩ
Shaft	120 mm × 12 mm, lead-free glass

IndSen 933, 934, and 941, for Strongly Acidic, Hot, and Viscous Media

The 933 with HF membrane is resistant to hydrofluoric acid, the 934 covers electroplating baths and high temperatures up to 130 °C with HA or PHY, and the 941 works with pre-pressurized gel at high pressures and with viscous liquids. All three use the Ag⁺ trap against poisoning by sulfide- or amino-acid-containing solutions.

Feature	IndSen 933	IndSen 934	IndSen 941
pH range	0 to 11 pH	0 to 13 pH	0 to 14 pH
Temperature	0 to 80 °C	0 to 130 °C	0 to 100 °C
Pressure	6 bar	10 bar	6 bar
Diaphragm	Open ×2	Open ×2	Ceramic ×1
Electrolyte	Polymer	Polymer	Pre-pressurized gel
Membrane	HF	HA or PHY	HA
Shaft	120 mm × 12 mm, lead-free glass

IndSen 405, for Biotechnology and Pharma

The pre-pressurized electrolyte prevents process medium from entering the reference system, and the electrode withstands repeated sterilization and autoclaving at 130 °C. Measuring range 0 to 12 pH, operating temperature 0 to 100 °C, pressure 2.5 bar, connection K8S or S8 with PG13.5 process connection, reference system Ag⁺ trap with ceramic ×1, HA membrane, shaft 120 or 225 mm × 12 mm made of lead-free glass. Versions: IndSen 405-P-120-K8S, 405-P-225-K8S, 405-P-120-S8, and 405-P-225-S8. The suffix P stands for the Swiss patented process, G for the standard process.

IndSen 3253 and 3253S, Sterilizable up to 140 °C

For life science and the pharmaceutical industry, with an integrated temperature sensor. PHY membrane and pre-pressurized gel withstand repeated sterilization at up to 140 °C with minimal zero-point shift. Measuring range 0 to 12 pH, operation 0 to 100 °C, pressure 4 bar, connection VP or P8, temperature sensor Pt1000 or Pt100. The 3253S additionally has a platinum sensor that acts as a solution ground to prevent measurement errors from ground potentials, while also serving as an ORP electrode.

IndSen 3250 and 3250S, for Biotech and Process Engineering

HA membrane and pre-pressurized electrolyte for biotechnology, pharmaceuticals, and chemical process engineering, resistant to high temperatures and alkaline solutions. Measuring range 0 to 14 pH, operation 0 to 100 °C, sterilization up to 130 °C, pressure 4 bar, connection VP or P8, temperature sensor optional. The 3250S includes the additional platinum sensor for solution grounding and ORP.

IndSen 4800, 4800F, and 4802, for Harsh Environments

Long service life in oxidizing media, strongly acidic or alkaline solutions, sulfide-containing media, and at high operating pressures. The impact-resistant 10-degree flat membrane of the 4802 better withstands solids-laden flows.

Feature	IndSen 4800	IndSen 4800F	IndSen 4802
pH range	0 to 14 pH
Temperature	0 to 130 °C
Pressure	10 bar	13 bar	13 bar
Reference system	PTFE ring	Long diffusion path	Long diffusion path
Electrolyte	Gel	Polymer	Polymer
Membrane	HA, cylindrical	HA, spherical	HA, 10-degree flat
Connection	VP, P8, or S3, PG13.5 process connection, solution grounding optional

IndSen 4260 and 4260F, for the Most Demanding Chemical Processes

Designed for high temperatures and pressures, solutions of low ionic strength, organic solvents, suspensions, emulsions, and protein-containing solutions, while being particularly insensitive to nitrates, sulfates, and carbonates. Measuring range 0 to 14 pH, 0 to 130 °C, 10 bar for the 4260 and 13 bar for the 4260F, reference system with a long diffusion path, diaphragm open ×2 or ceramic and open respectively, high-temperature-resistant polymer electrolyte, HA membrane.

IndSen 812 and 822, for Environmental Applications

pH measurement in surface water and wastewater, 0 to 14 pH, 0 to 80 °C, 6 bar. The 812 works with a ceramic diaphragm and Ag⁺ trap, the 822 with a PTFE ring, double diaphragm, and long-life reference system. Temperature sensor optionally none, Pt1000, Pt100, or NTC30k, shaft 12 × 120 mm made of lead-free glass.

IndSen 600 Series, with PPS Housing and 3/4-NPT Thread

For surface water, wastewater, and industrial wastewater, offering the best price-performance ratio of the product lines. The PPS (polyphenylene sulfide) housing is highly temperature-resistant, highly insulating, and close to PTFE in corrosion resistance. Available as a pure pH electrode, as pH plus temperature, and as pH plus temperature plus grounding electrode, with a fixed cable or as a split version with P8 connection and AP9 connecting cable.

Feature	IndSen 632 and 638	IndSen 632P and 638P	IndSen 622 and 628
pH range	0 to 14 pH
Temperature	0 to 100 °C	0 to 100 °C	0 to 80 °C
Pressure	7 bar
Reference system	Long-life reference with second diaphragm
Diaphragm	Outer PTFE ring and open ×2, inner ceramic
Electrolyte	Outer polymer, inner gel
Membrane	632: HA cylindrical, 638: HA 8-degree flat	Same as 632 and 638	Conventional measuring membrane, spherical
Recommended use	Forced-circulation desulfurization, harsh chemical processes	Desulfurization, high pressure and solids content	Environmental protection and water treatment
Design	27 × 142 mm, 3/4-14 NPT, solution grounding optional as platinum pin

IndSen 500 Electrode Sleeves

Industrial PPS electrode sleeve, heat- and chemical-resistant. It protects glass electrodes in the process and extends their service life. Can be used with various IndSen pH and ORP electrodes for immersion and flow-through measurement, dimensions 27 × 142 mm, process connection 3/4-14 NPT top and bottom, electrode mount via PG13.5 thread with sealing ring.

Want to Measure Individual Ions Instead of pH or Redox?

The IndSen series also includes ion-selective electrodes for 13 ions, including nitrate, ammonium, fluoride, chloride, and several heavy metals. They work with ultra-durable PVC, solid-state, or single-crystal membranes and are available digitally or in analog form.

Connections, Cables, and Installation

The suffix of the electrode designation indicates the cable length, for example Cab/3 for a 3 m cable. The same applies to cables, for example AS9/3 for 3 m.

Model	Thread	Connecting Cable	Number of Poles	Cable Length
Cab	No thread	Fixed cable on the electrode	–	1 to 15 m
S3	PG13.5	Fixed cable on the electrode	–	1 to 15 m
S8	PG13.5	AS9	2-pole	1 to 15 m
P8	PG13.5	AP9	8-pole	1 to 15 m
VP	PG13.5	VP6	2- to 6-pole	1 to 15 m

Four variants are available for installation: top-mounted, side-mounted, flow-through mounting with inlet and outlet, and immersion mounting. With immersion mounting, you should regularly check for water ingress. For easy cleaning and maintenance, it’s best to install the electrode in a bypass, so it can be removed without interrupting the process.

Which Series Fits Which Application?

This overview is an initial guide. The final selection also depends on pressure, process connection, cable routing, and the transmitters already in place.

Application	Recommended Series	Why
Surface water and cooling water	912, 931, 812, 822, 600 series	Low-fouling diaphragms and rugged housings
Drinking and pure water, low ionic strength	915, 925, 919	L membrane with low impedance, salt reserve against drift
Measurement at low temperatures	917	Gel III doesn’t freeze at -30 °C
Neutralization and industrial wastewater	912, 931, 600 series	HA membrane with low alkaline error
Hydrofluoric-acid-containing media	933	HF glass membrane
Electroplating and high temperatures	934	PHY or HA membrane up to 130 °C
High pressure and viscous media	941, 4800, 4802	Pre-pressurized gel, pressure-resistant designs up to 13 bar
Biopharmaceuticals, upstream and downstream	405, 3250, 3253	Sterilizable and autoclavable, 3253 up to 140 °C
Flue gas neutralization and desulfurization	632, 638	PPS housing, pressure- and fouling-resistant reference system
Solids-laden streams	4802, 638	Impact- and abrasion-resistant flat membrane
Organic solvents, emulsions, proteins	4260, 4260F	High-temperature polymer electrolyte with open junction
Food, beverages, and CIP	3250, 3253, 934	Resistant to cleaning and sterilization cycles
Multi-point measurement with central display	pH digital module and P8 electrode	RS485 bus operation, calibration data stored in the module
Redox measurement in the process	316, 317, 334	Platinum or gold ring, up to 130 °C and 10 bar
Ion measurement, e.g. nitrate or ammonium	2071S, 2071M, 1121M	Ultra-durable PVC, solid-state, or single-crystal membrane

Is your application not listed in the table? Ongoing pH monitoring in the process brings many special cases with it. Contact us and we’ll adapt the electrode for you.