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Ceramic Thick Film Pressure Sensors

These are a type of sensor which utilises a measurement technology that comprises of a ceramic diaphragm and thick film strain gauges to measure pressure.

Ceramic thick film strain gauge pressure sensing module

The ceramic diaphragm is a thin, flexible material that is sensitive to changes in pressure. The thick film strain gauges are resistive elements that are printed onto the ceramic diaphragm to form a Wheatstone bridge circuit. When pressure is applied to the diaphragm, it deflects, which causes the strain gauges to change resistance. This change in resistance causes a voltage drop across the bridge which is proportional to the applied pressure.

Ceramics do not react with most chemicals, making them a great choice for chemical processing applications.

It is an excellent electrical insulator which provides a base substrate for printing conductive materials to provide electrical function such as a strain gauge Wheatstone bridge circuit.

It is a very hard material, with an extremely high resistance to abrasion. It’s made from tightly packed and bonded crystalline material, and provides superb protection from media which contain abrasive particles such as slurries and liquids which contain sediment.

Advantages

  1. Cost-Effective: The simple design and manufacturing process of ceramic sensors make them more affordable than other pressure sensor technologies.
  2. Chemical and Abrasion Resistance: Their robust nature makes them ideal for challenging environments.
  3. Compact & Hygienic: The lack of oil-filled seals or complex internal components makes them compact and easy to clean.
  4. Non-Metallic: Suitable for applications where metallic components are undesirable.

Disadvantages

  1. Lower Accuracy: Compared to some other pressure sensor types, ceramic sensors may offer slightly lower accuracy.
  2. Lower Signal-to-Noise Ratio: This can be a consideration in applications requiring very high precision or sensitivity.
  3. Limited Pressure Ranges: Ceramic sensors are typically not suited for extremely high or extremely low pressure ranges.
  4. Vulnerability to Surface Damage: While resistant to abrasion, the diaphragm’s surface can be damaged by sharp impacts.
  5. Elastomer Seals: The use of elastomer seals (instead of welded components) can be a limitation in certain high-temperature applications.

Applications

The unique properties of ceramic diaphragm thick film strain gauge pressure sensors make them well-suited for a variety of industrial applications:

  • Caustic Chemical Processes & Storage: Their chemical resistance makes them ideal for measuring pressure in harsh chemical environments.
  • Original Equipment Manufacturer (OEM) Design: Their compact size and affordability make them a popular choice for integration into various equipment and machinery.
  • Industrial Printers: The corrosion resistance of ceramic sensors is advantageous in the demanding environment of industrial printers where there are hazardous and aggressive chemicals present.
  • Water and Wastewater Treatment: Ceramic sensors’ resilience is useful in monitoring pressure in water and wastewater systems.
  • Food and Beverage Processing: The hygienic design of ceramic sensors makes them suitable for applications involving food and beverages.

FAQ

Questions and Answers about ceramic diaphragm with thick film strain gauge pressure sensor technology.

Sensing Diaphragm Material & Performance

How well does the sensing diaphragm material perform for elasticity, hysteresis, repeatability and robustness?

Ceramic is a very hard material, but the range of elasticity is limited, and it is more vulnerable to cracking and rupture than other technologies.

Media Compatibility

How protected is the pressure sensor module assembly against different types of aggressive media, and how customisable is the construction to enhance protection to a particular media type?

The diaphragm, made from ceramic—a hard, chemically inert material—offers high corrosion resistance to hazardous chemicals, including acids and bases. It’s typically housed within a metal or plastic casing that also incorporates the process connector. An elastomer seal creates a barrier between these two components. This design flexibility allows for adaptation to almost any media type by selecting compatible materials for the elastomer seal and process connector.

Oil Leakage

Is there a risk of oil leakage from this sensor, which could impact performance or safety?

Ceramic sensing modules are compatible with most media, eliminating the need for an oil-filled isolation diaphragm to protect the sensing element. Their size and rigidity allow for direct mounting within a process connector, using an O-ring to create a pressure seal. All wire connections are made to PCB solder pads on the module’s reverse side.

Pressure Containment

How well are the internal components joined together to provide a seal to withstand pressurisation that exceeds normal operating conditions, without degradation due to pressure and temperature cycling over the lifetime of the sensing device?

Elastomer O-rings, used to seal between the ceramic diaphragm and process connector, are the most likely component to fail and compromise pressure containment. While they provide a sufficient seal for low to medium pressure ranges and protect the ceramic from differential thermal expansion, exposure to certain fluids or extreme temperatures can compromise their sealing performance. These conditions can cause physical changes in the elastomer, softening or hardening it, and reducing its effectiveness as a seal.

Small Size

How small a pressure sensor is it possible to make with this sensing technology?

Ceramic diaphragm material has a minimum thickness limit to maintain its elastic properties. This, in turn, limits the minimum achievable diameter, as altering either thickness or diameter independently affects the operating pressure range.

Additionally, the lower output sensitivity and higher noise levels of thick-film strain gauges necessitate a certain size to ensure a sufficient output signal. Typically, the sensor module is around 1 inch (25mm) in diameter, but it’s possible to achieve sizes as small as 10mm for higher pressure ranges starting from a few bar.

Corrosion Resistance

How resistant are the media exposed materials to corrosive substances?

Ceramic is highly resistant to most chemicals including acids and base chemicals, providing excellent protection from chemical corrosion, and extending the service life of pressure sensors used in the chemical processing industry, waste management & treatment, marine environment.

Abrasion Resistance

How resistant are the media exposed materials to abrasive substances?

Ceramic is a very hard material and highly resistant to being marked or pitted from fast moving small particles in gases such as dust or powders, or liquids containing solids such slurries or pulp.

High Pressure Spikes

What are the chances of a noticeable effect on the sensors operational performance, or damage to the sensors internal components, from exposure to very dynamic or quickly changing pressures, such as hydraulic pressure spikes or water hammer?

The ceramic diaphragm’s stiffness and limited elasticity make it vulnerable to damage from high-frequency pressure shocks that significantly exceed its pressure range. These shocks concentrate a large amount of energy in a fraction of a second, leading to irreparable damage like cracks or ruptures in the diaphragm’s surface.

Overpressure Handling

How affected is the accuracy performance of the sensor by an overpressure condition, where the pressure exceeds 100% of range?

The overpressure tolerance of these sensors is constrained by the limited elastic range of the ceramic diaphragm, which increases the risk of fracture under excessive pressure. Additionally, the diaphragm thickness required for adequate output sensitivity with thick-film strain gauges further restricts the overpressure rating, necessitating a more conservative design approach.

Very Low Pressure Ranges (<100 mbar)

How well does it perform measuring very low pressures with a pressure range lower than 100 mbar?

Output sensitivity is greatly reduced with very low ranges due to limitations on how thin the diaphragm can be while maintaining sufficient elasticity without fracturing. This also impacts accuracy due to increased temperature errors, vibration noise, and a noisier signal resulting from the lower output sensitivity.

Low Pressure Ranges (100-1000 mbar)

How well does it perform measuring low pressures with a pressure range between 100 and 1000 mbar?

The output sensitivity at lower pressure ranges is suboptimal, similar to the behavior at very low pressure. The noise levels also remain relatively high, making it challenging to match the performance of silicon strain gauge and ceramic variable capacitance sensor technologies.

Medium Pressure Ranges (1-100 bar)

How well does it perform measuring medium pressures with a pressure range between 1 and 100 bar?

The best balance of stiffness and strength is achieved at moderate pressure ranges, providing high sensitivity and low noise without excessive diaphragm deflection, all while staying within the normal operating range.

High Pressure Ranges (100-1000 bar)

How well does it perform measuring high pressures with a pressure range between 100 and 1000 bar?

The best balance of stiffness and strength is achieved at high pressure ranges, providing high sensitivity and low noise. However, overpressure limitations become a concern due to the lower strength of ceramic diaphragms compared to the metal diaphragms used in bonded foil or thin-film strain gauge pressure sensor.

Very High Pressure Ranges (>1000 bar)

How well does it perform measuring very high pressures with a pressure range greater than 1000 bar?

At very high pressures, the lower tensile strength of ceramic diaphragms compared to metal-based diaphragms significantly increases the risk of cracks and sensor failure. This limitation restricts both the achievable pressure range and the overpressure margin as operating pressures approach the upper engineering design limits.

Elastomer seals, used to secure the ceramic diaphragm within the process connector, present a higher pressure containment risk compared to the all-welded designs typically employed in metal-based sensor technologies for high-pressure applications.

Absolute Pressure Ranges

Can this sensor technology be easily adapted to measure absolute pressures, or pressures referenced to a hard vacuum?

Absolute ranges necessitate a flush-mounted diaphragm design instead of the simpler monolithic design. This allows for sealing a vacuum between the sensing diaphragm and the integrated PCB, separated by a ceramic ring support, forming a capsule.

Accuracy

What level of accuracy performance is achievable from the combined effects of linearity, hysteresis, short term repeatability, temperature errors, and long term stability?

The accuracy performance is limited by a less precise manufacturing process and the use of different materials for the strain gauges and diaphragm. These materials tend to be softer and less uniform than those used in other technologies. Additionally, the printed strain gauges pose a greater risk of delamination compared to implanted strain gauges such as thin-film or semiconductor types, further contributing to lower accuracy.

Output Sensitivity

What is the level and quality of the output produced from the transducer technology, before any signal conditioning electronics is added?

The use of larger, thicker strain gauges and limited diaphragm deflection to prevent fractures result in lower output sensitivity compared to other pressure sensor technologies. This reduces the overall output signal before signal conditioning. Additionally, the composition of thick-film strain gauges leads to noticeably higher noise levels on the output due to fluctuations in the electrical current flow.

Frequency Response

How quickly does the sensor’s output respond to changes in pressure?

The response time of variable capacitance ceramic diaphragm technology is relatively slow compared to thin-film or silicon chip strain gauge technologies. This is primarily attributed to the larger and heavier diaphragm, which exhibits higher inertia, impeding its rapid movement in response to pressure changes. Additionally, the signal conditioning process, which involves rectifying and filtering an AC signal to generate a DC output, introduces further delays due to the inherent time constants of these filtering circuits.

Compare with other pressure sensor technologies

How do pressure sensors that use a ceramic diaphragm with thick film strain gauges compare to other technologies?

Sensing technology Si-Chip Si-Isolated Thick-Film Var-Cap Thin-Film BFSG
Sensing diaphragm material Excellent Excellent Fair Fair Good Good
Media compatibility Bad Good Excellent Excellent Good Good
Oil fill leak risk Excellent Bad Excellent Excellent Excellent Excellent
Pressure containment Poor Good Fair Fair Excellent Excellent
Small size Excellent Good Fair Poor Good Fair
Corrosion resistance Bad Good Excellent Excellent Fair Fair
Abrasion resistance Bad Bad Excellent Excellent Fair Fair
High pressure spikes Bad Poor Fair Poor Good Good
Overpressure rating Good Excellent Fair Good Poor Poor
Very low pressure < 100mb Good Poor Bad Good Bad Bad
Low pressure 100…1000mb Good Good Poor Good Bad Bad
Medium pressure 1…100bar Fair Excellent Excellent Fair Good Fair
High pressure 100…1000bar Bad Good Fair Bad Excellent Good
Very high pressure > 1000bar Bad Bad Bad Bad Good Excellent
Absolute pressure ranges Fair Excellent Good Good Bad Bad
Accuracy Excellent Good Poor Fair Good Fair
Output Sensitivity Excellent Excellent Fair Excellent Good Fair
Frequency response Excellent Good Fair Poor Good Fair
Comparison rating (90 max) 56 63 59 61 62 57

Which technology to use for your application?

Find out whether ceramic thick film pressure sensors will be the most suitable choice for your application compared to other technologies.

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Checklist for ceramic thick film pressure sensor requirements

Define your ceramic thick film pressure sensor requirements using this checklist:

  1. Pressure range?
  2. Overpressure?
  3. Output signal?
  4. Dynamic response?
  5. Accuracy?
  6. Electrical connection?
  7. Process connection?
  8. Size dimensions?
  9. Process media type?
  10. Media temperature range?
  11. Environment temperature range?
  12. Environment shock and vibration?
  13. Shock pressures?