Application Notes

Aircraft & Aerospace Sensors

Space Qualified Sensors

RdF has proudly every manned U.S. space mission beginning with NASA’s earliest flights.

Thousands of RdF’s designs are currently in orbit on satellites, telescopes, and the International Space Station (ISS). Their RTD’s, Heaters, Thermocouples, Reference Junctions, and other components are qualified to the most rigorous environmental conditions, these include:

  • RTDs for Cryogenic Fuels, Rocket Nozzles, Vehicle Structures and Skins
  • Sensors and heaters for electronics
  • Sensors for re-entry shields
  • Low outgassing and low mass construction
  • Catalog Sensors with Flight Heritage
  • Proven performance in high shock, vibration and flow

Testing Instrumentation

RdF provides RTDs, Thermocouples, Heat Flux, and Thermal Sensors used on a wide range of testing in flight, on test stands and in laboratory settings.


  • Temperatures cryogenic to 480°C (900°F)
  • Probes and capsules as small as 0.066” (1.7mm) OD
  • Surface mount design with a thickness of <1.27mm (0.05”)
  • Secondary standards accuracy, NIST-traceable calibration


  • Used cryogenic to 1150°C (2100°F)
  • Probes and surface mount configurations
  • Foil TCs as thin as 13μm (0.0005”) for response in milliseconds
  • Special limits of error–types E, J, K, T

Heat Flux Sensors:

Thin Foil Gauges

  • Flexible
  • As thin as 76μm (0.003″)
  • Response time <0.1 seconds
  • Range 0-50 BTU/Ft2 sec

including Calorimeters and Radiometers

RdF Corporation is the world’s leading innovator in the design, development and production of surface, insertion and immersion temperature and heat flux sensors. Their multi-market innovations are especially important as applied in demanding aerospace and military applications. Most of the newest surface and immersion temperature sensors in use were originally introduced, engineered and manufactured by RdF.


RdF supplies sensors monitoring turbine inlet and inter-stage turbine temperature on many of the world’s aircraft. Dependable operation over thousands of starts, stops and thermal cycles demands the reliability delivered by RdF’s thermocouples and RTDs. RdF also holds FAA-PMA approvals for manufacturing sensors to the Aftermarket.

Fuels & Fluids

RdF sensors monitor temperature in fuel and main oil systems, as well as hydraulic fluid systems. Their RTD’s are installed in various assemblies including level-sensing and flow measurement. For fuel temperature applications, their sensors have been designed for line-mounting and full immersion in the tank.

Air Temperature

RdF air sensors provide accurate measurements for critical applications in environmental control systems, controlled chambers, wind tunnels, cargo bays, air intakes, heat exchangers, and exhaust flues. Configurations vary depending on system requirements, from simple sheaths to perforated sheaths, with either thermistors or RTDs covering a broad temperature range.

Transparencies & Structures

RdF’s resistance temperature sensors are integrated into the de-icing systems of commercial and military aircraft. Standard and custom components are incorporated into leading edge and rotor blade assemblies as well as various composite components use throughout the aircraft. Transparent wire-wound grids or point-sensitive RTDs are laminated into windshields and canopies with high optical clarity requirements. The stability and repeatability of RdF’s sensors mean consistent and reliable readings over the aircraft’s service life.

Cryogenic Aerospace RTDs

RdF offers a broad range of Cryogenic RTD Probes for ground support and flight. We tailor designs and qualify sensors to meet varying performance requirements and environmental conditions for each program. RdF RTDs have served on every manned US Space Mission since Project Mercury.

Cryogenic RTDs for Aerospace often have application-specific demands that are met with different design options. These particulars will vary and should be discussed with RdF to identify the right sensor. Examples of such considerations are:

• Dynamic Requirements, shock vibe and flow
• NIST Traceable Cryogenic Calibration for High Accuracy Control Points

Typical Performance RangeConstruction Features
Temperature Range-320°C to 200°C Max (-434°F to 500°F)Hermetically Sealed
Standard AccuracyTyp ±1.1°C Over Temp RangeAll-Welded Metal Construction
Special Accuracy±0.14°C at Custom CalibrationThread Mount AS5202
Pressure Rating2,500psi - 5,000psi OperatingLockwire Holes
Resistance at 32°F / 0°C100Ω, 1000Ω, 2000ΩTypical Connector D38999 or Custom
Sensor StyleFeaturesNotes
A - Straight sheath probe
A Straight sheath probe
  • Response Time 3 seconds
  • 0.25" Outer Diameter
  • 6", 12" Probe Length
  • Connection: Leads or Connector

General Use Ground Support Design
Installation with Swagelok Fitting

B - Stepped sheath probe
B - Stepped sheath probe
  • Response Time 1-2 seconds
  • 0.125" to 0.188" Tip Outer Diameter
  • Configurable Length, 2" and up
  • Process Thread Mount

General Use Design
Robust constuction, well suited for high flow measurement

C - Small diameter probe
C - Small diameter probe
  • Response Time 1 second
  • 0.093" to 0.125" Tip Outer Diameter
  • Configurable Length, Up to 2"
  • Process Thread Mount

General Use Design

D - Flat responce probe
D - Flat responce probe
  • Response Time 0.5 seconds
  • Variable Tip Outer Diameter
  • Configurable Length, from 1.5"
  • Process Thread AS5202

Available with and without Tip Shield based on flow conditions
Stainless or Inconel construction typical
Connector D38999

E - Hollow Annulus Probe
E - Hollow Annulus Probe
  • Response Time 0.3 seconds
  • 0.33" Outer Diameter
  • Configurable Length, 3" -6"
  • Process Thread AS5202

Robust constuction, well suited for high flow measurement

Calibration Capabilities

RdF maintains a NIST-traceable calibration facility to support the high accuracy requirements of our Research, Defense, Aerospace and Nuclear customer base.
For many applications, RdF recommends a standard three-point calibration at Liquid Nitrogen, 0°C and 100°C to provide reliable and repeatable measurements ±1.1°C over a wide range.
For customers with super high-accuracy sensing needs, RdF Corporation offers multipoint cryogenic calibration services and individualized Resistance v Temperature profiles in the cryogenic range for each probe. Calibration points can be customized to application-specific control points.
Using our NIST-Calibrated Cryogenic Standards, RdF’s calibration process yields RTD Probes with accuracies ±0.14°C, high interchangeability, and extremely stable, repeatable performance.

RdF Aerospace Legacy

Founded in 1955, RdF has supported space exploration since the inception of the United States Space Program. RdF sensors have served on every manned U.S. space mission since Project Mercury.
Their qualified temperature sensors are orbiting on the ISS, satellites, and telescopes, installed in ground support facilities, and monitoring critical systems on launch and crew vehicles currently in production.
Today, RdF continues to work with companies worldwide to advance the exploration of Space. To discuss your project or learn more about RdF’s Cryogenic Capabilities, please speak to one of our engineers.

What is hydrogen?

Hydrogen (H) is the first element on the periodic table and is the most abundant gas in the known universe. Each atom of hydrogen consists of only one proton. Despite this, there is no natural hydrogen produced on Earth as it is only found in a combined form. Water (H2O), for example, is a combination of hydrogen and oxygen. Hydrogen is also found in other forms such as hydrocarbons which are contained within fuels such as petrol, diesel, natural gasses, methanol, and propane.

Hydrogen is not actually an energy source itself, but instead an energy carrier. For this reason, hydrogen has a unique and often, at times, misunderstood role in the global energy system. One of the most significant advantages of hydrogen is that it is very efficient, approximately three times more efficient than gasoline.

One of the biggest challenges with hydrogen is obtaining it in its pure form.  Although Hydrogen is a green fuel during its usage, cracking hydrogen from its compound form requires a large amount of energy. At the current time, around 84% of the world’s energy is still derived from fossil fuels. This results in greenhouse gas emissions and air pollutants which lessen the overall environmental benefits of hydrogen power. There is also still the issue of safely storing and transporting this volatile element. There are however many schemes and government directives that are pushing for more and more renewable energy as well as ongoing projects within various companies to develop safer ways of transporting and using hydrogen. Along with a greener energy source, we are also able to produce hydrogen from biological hydrogen production, a process where carbohydrate-rich and non-toxic raw materials are broken down by anaerobic and photosynthetic microorganisms, producing hydrogen as a byproduct of this process.

Hydrogen as a form of energy carrier is not new,  powering the first internal combustion engines over 200 years ago and becoming a fundamental part of the refining industry. It has some positive benefits being light, storable, energy-dense and only having water as a by-product. Hydrogen could be the key to unlocking a carbon-neutral future. However, for this to happen it needs to be adopted into the larger industries and sectors where fossil fuels and nuclear energy are currently being used such as transport, buildings and power generation.

Can hydrogen be used as a fuel for vehicles?

A fuel cell is an electrochemical cell, that produces electricity by converting chemical energy into electrical energy. When hydrogen and oxygen are combined within a fuel cell, heat and electricity are produced, with water vapour produced as a by-product.

Fuel cells have the potential to power electric motors (used within various modes of transportation),  provide energy for systems as large as a power station or charge something as small as a mobile phone.

As with battery-electric vehicles (BEV), hydrogen fuel cell electric vehicles (FCEVs), including cars, vans, buses and lorries are powered by electricity, so produce no harmful emissions including carbon dioxide (CO2) from their tailpipe. Only water vapour is produced from hydrogen fuel cell electric vehicles. In FCEVs, energy is stored in the form of compressed hydrogen fuel, rather than in a battery. Hydrogen can be stored and transported at high energy density in liquid or gaseous form.

In hydrogen fuel cell electric vehicles (FCEVs) the fuel cell converts compressed hydrogen from their fuel tanks into electricity that powers the electric motor in the vehicle.

A fuel cell coupled with an electric motor is two to three times more efficient than an internal combustion engine running on gasoline. Therefore FCEVs have the advantage of being able to cover longer distances, and only take a few minutes to refuel at a retail site, unlike BEVs that take a long time to recharge in comparison with a much shorter range.

Pressure sensors for hydrogen applications

With the demand for hydrogen fuel cell-powered vehicles and equipment increasing, so does the need for hydrogen-compatible equipment and components. Core Sensors, a leading manufacturer of pressure and temperature transducers, produce a range of specialist pressure sensors capable of monitoring the dispensing and storage of hydrogen.

There are some known difficulties when working with hydrogen in its gas form, so selecting the correct sensor configuration is a key factor in the planning process. Two of the biggest concerns are hydrogen embrittlement and hydrogen permeation.

Hydrogen embrittlement is the degradation of a sensor diaphragm’s metal properties caused by hydrogen. To avoid this, choose the optimum sensor materials. Materials to avoid are 17-4 stainless steel and nickel-based alloys like Inconel 718.

Hydrogen permeation happens when hydrogen atoms (H2) separate into hydrogen ions (H+) under specific conditions like high pressure and temperature. These hydrogen ions can pass through the sensor diaphragm’s molecular structure.

To overcome these complications, Core Sensors have designed a range of pressure sensors, transducers and transmitters, providing a high-quality and long-life solution for your hydrogen application.

Design & Materials selection

Fluid filled sensor diaphragms are highly susceptible to hydrogen permeation and should be avoided. Hydrogen ions that pass through the thin diaphragm will form hydrogen bubbles in the fill fluid causing zero and span shifts. Over time these bubbles can expand and cause the diaphragm to bulge and eventually fail, resulting in the fill fluid leaking and contaminating the process.

To avoid having fluid filled cavities, sealing materials such as O-rings or welded joints, Core Sensors can manufacture their sensors using a single piece of 316L stainless steel. This solid piece of stainless steel then contains the hydrogen within the pressure port, reducing the possibility of the media permeating the thin diaphragms that are common in oil filled sensor designs.

High-pressure hydrogen measurement

Hydrogen is compressed to a high pressure, typically 350 Bar (~5,000 PSI) and 700 Bar (~10,000 PSI), to help increase the amount of hydrogen that can be stored on site. Highly reliable pressure sensors are required to safely monitor these tanks and other high pressure hydrogen applications. Core Sensors offer an F250C female autoclave process connection option for pressures >10,000 PSI. This process connection features all 304 and 316L stainless steel wetted parts to ensure protection from embrittlement and permeation, resulting in a long term monitoring solution.

  • Storage
  • Fuel Lines
  • Dispensers
CS50 with an F250C Female Autoclave process connection and Mini-Fast electrical connection
CS50 with an F250C Female Autoclave process connection and 1/2″ MNPT conduit w/ cable
  • High Strength
  • 316L Stainless Steel
    UNS S31603
  • All welded metal construction
    No internal elastomer seals
  • Area Classification
    CSA Class I, Division 2 Non-Incendive Groups A, B, C, D T4
  • Marine ABS Approvals
  • CE
F250C Female Autoclave process connection in all 304 & 316L SS
Variety of configurations available (DIN 43650, Form A, Turck® Mini-Fast®, 1/2” MNPT conduit w/strain relief

Industrial applications

For industrial applications where hazardous certification approvals are not required, the CS10 Industrial Pressure Transducer can be packaged to meet the demands of hydrogen environments. Pressure ranges are available from 50 PSI up to 20,000 PSI in solid 316L SS. Customers have the choice of various output signals including 4-20mA loop powered for long-distance transmissions and voltage outputs for low power and low current consumption applications. A variety of electrical connections are available from standard DIN connections to M12x1 and integral cable for a higher IP67 rating. Custom configurations are available for OEM projects.

Hazardous – Non-incendive

Some applications require non-incendive approved equipment, the CS50 Non-Incendive Pressure Transducer is an ideal solution to this and can be configured with 316L stainless steel material and various other options. The CS50 is approved for the following standards:

  • CSA Class I, Division 2, Groups A, B, C, D T4
  • ANSI/UL 122701 Single Seal
  • ABS (American Bureau of Shipping)
  • CE

Common model number configurations

To best suit your application and installation requirements, Core Sensors are able to customise the configuration of the below parts that are typically used in hydrogen fuel cell applications.

Model NumberDescriptionTypical Use
View CS10 specifications
0-20 Bar, 3/8-24 UNF-2A Male process connection, 0.5-4.5V ratiometric output signal (5VDC regulated power supply), Packard Metripack 150, 316L SS wetted material, GaugePost regulator pressure into PEM (Proton Exchange Membrane)
View CS10 specifications
0-20 Bar, 7/16-20 UNF Male process connection, 0.5-4.5V ratiometric output signal (5VDC regulated power supply), Packard Metripack 150, 316L SS wetted material, Gauge Post regulator pressure into PEM (Proton Exchange Membrane)
View CS10 specifications
0-448 Bar, 3/8-24 UNF-2A Male process connection, 0.5-4.5V ratiometric output signal (5VDC regulated power supply), Packard Metripack 150, 316L SS wetted material, Sealed GaugeHigh pressure Hydrogen storage
View CS10 specifications
0-448 Bar, 7/16-20 UNF Male process connection, 0.5-4.5V ratiometric output signal (5VDC regulated power supply), Packard Metripack 150, 316L SS wetted material, Sealed Gauge High pressure Hydrogen storage


Hydrogen. (n.d.). Shell.

Hydrogen. (2022). Student Energy.

Hydrogen Pressure Sensors – Industrial & Hazardous. (n.d.). Core Sensors.

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