What exactly is an oxygen probe?

An oxygen probe is an electrolytic cell that converts the difference in the partial pressure of oxygen between two separate gases into a voltage. The electrolyte is a ceramic body that separates the measuring side from the reference side. Ambient air, containing approximately 21% oxygen, is usually used as the reference. The voltage is calculated using the Nernst equation.

Can I measure elements other than oxygen?

An oxygen probe measures only the partial pressure of oxygen. In known processes, the oxygen content can be used, for example, to calculate an approximate value for the carbon content during carburization. However, this is only a mathematical approximation and requires precise knowledge of the gas mixture.

What are oxygen probes used for in practice?

Industrial oxygen probes are used in heat treatment facilities to control the process atmosphere, for example, during hardening by carburizing or nitriding. They regulate the amount of carbon or nitrogen in the atmosphere.

What is the difference between an oxygen sensor and a lambda sensor?

There is no fundamental difference: A lambda sensor is a heated oxygen sensor for exhaust gases from internal combustion engines. Both use the same technology to measure oxygen based on the electrochemical effect.

Why do Thermo-Control oxygen probes only work at temperatures of 500 °C or higher?

The ceramic electrolyte must be conductive so that oxygen ions can diffuse through it—this is only possible at temperatures of approximately 500 °C or higher. thermo-control probes are designed for high-temperature processes without an integrated heater. An external heater would be required for lower temperatures.

High-Precision Oxygen Probes for Industrial Furnaces

Precise oxygen measurement in industrial furnaces? Thermo-control’s industrial oxygen probes offer a reliable and durable solution in the temperature range of 480–1300 °C. Our probes are available in various designs and models to provide the right solution for every application.

All oxygen probes manufactured by thermo-control Körtvélyessy GmbH are synonymous with the highest quality and decades of expertise. They are designed according to the following principles:

✓ All-ceramic restoration
✓ Suitable for a temperature range of 480 °C to 1300 °C
✓ Wires and connectors made of pure platinum
✓ Solid, one-piece FZY electrolytes
✓ Integrated Type S thermocouple
✓ Type A Connection Head
✓ Standard lengths: 400 mm – 1000 mm
✓ No external reference air supply required

For more technical details and available models, please see our catalogs or the Frequently Asked Questions section.

Complete Catalog of Oxygen Probes

The catalog contains all standard models of our oxygen probes and accessories—including order codes, technical specifications, overview diagrams, and part numbers. Ideal for planning, selection, and ordering.

Download the complete catalog as a PDF now (~5.5 MB)

Nernst Equation – Oxygen Probes & Thermovoltage

The Nernst equation describes the relationship between the partial pressure of oxygen and the voltage generated in the oxygen sensor.

Thermo-control's oxygen probes are based on Nernst's law, which states that a concentration gradient separated by an electrolyte generates a voltage.

This physical law applies to all oxygen probes; however, it is up to the probe's design to maintain constant conditions.

As with the thermocouples, Dr. Körtvélyessy introduced technical innovations here as well, which made the thermo-control oxygen probe an outstanding product.

The response time, reliability, and durability of thermo-control oxygen probes are currently unmatched.

O₂

Nernst calculator

Calculate probe voltage and oxygen potential relative to reference air.

Temperature °C Probe voltage

Oxygen

ppm

pO₂ 1.000e-6 bar Reference 20.95 % O₂

The calculation assumes equilibrium conditions and reference air at equal total pressure.

Carbon potential calculator

Calculate the relationship between furnace temperature, zirconia-probe voltage and carbon potential.

Temperature

°C

Probe voltage

Carbon potential

% C

CO concentration

Vol. %

CO factor

COF

Calculated equilibrium reference value. The actual carbon potential depends on furnace atmosphere, load, gas circulation, furnace geometry and process conditions. The CO factor should be determined for the particular installation.

Variants

Inert Gas-Oxygen Probes

For carburizing and carbunitriding

Vacuum-Oxygen Probe

For Plamsan soldering or vacuum soldering

Accessories

Air supply, isolating amplifiers, or display devices

Inert Gas-Oxygen Probes

Pressure range: 10⁻² mbar to 2 bar

Built-in PtRh-Pt thermocouple with a 4-year warranty
Temperature range from 500 °C to 1300 °C
Standard process connection via G3/4″ thread or Ø22 × 150 mounting tube
Custom process connections available upon request
Gas-tight and pressure-resistant up to 2 bar
Includes a performance test certificate with test points at 940 °C using N2H2 (5%)
Optionally available with a calibration certificate in accordance with AMS 2750
Pre-assembled with cables and connectors upon request

Select the appropriate model

Inert Gas Oxygen Probe with G3/4-inch Process Thread

Vacuum-Oxygen Probe

Pressure range: 10⁻⁴ mbar to 5 bar

Built-in PtRh-Pt thermocouple with a 4-year warranty
Temperature range from 500 °C to 1300 °C
Standard process connection via ISO 2861 small flange DN 25 or Ø22 × 150 mounting tube
Custom process connections available upon request
Vacuum-tight and pressure-resistant up to 5 bar
Includes a performance test certificate with test points at 940 °C using N2H2 (5%)
Optionally available with a calibration certificate in accordance with AMS 2750
Pre-assembled with cables and connectors upon request

Select the appropriate model

Accessories

For use with thermo-control oxygen probes

Air Supply Units
Panel Displays
Splitter amplifier

Select the Right Accessories

Open-air supply unit with compressed air supply

Documents on Thermo-Control oxygen probes

Complete Catalog of Oxygen Probes

3.2 MB

Inert Gas-Oxygen Probes, Threaded

571 kB

Catalog: Inert Gas and Oxygen Probe Holder Tube

Inert Gas-Oxygen Probe Holder Tube

378 kB

Vacuum-Oxygen Probe Holder Tube

571 kB

Small-Flange Vacuum-Oxygen Probes

571 kB

Oxygen Probe Accessories

426 kB

General Information About Oxygen Probes

264 kB

Instructions for Use: Threaded Inert Gas Probe

264 kB

Frequently Asked Questions About Oxygen Probes

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