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Technology overview

Ceramic capacitive

The most important element of the ceramic capacitive technology is the ceramic (Al2O3) measuring cell. After assembly, the ceramic cell element resembles a plate capacitor with a reference electrode and a measuring electrode placed 0.01 mm apart. The capacitance is inversely proportional to the distance between the electrodes. As pressure is applied, the distance changes by a small value and the capacitance changes proportionately. This signal is then converted into pressure by a microprocessor.

Features:

  • Pressure ranges from 100 mbar (40 “H2O) to 600 bar (8700 psi). Vacuum to -1 bar (-14.5 psi)
  • Extremely robust with high over pressure and burst pressure rating
  • Drift-free operation > 100 million pressure cycles
  • High long-term stability and repeatability
  • Only suitable for low pressure gases (<25 bar / 363 psi) due to elastomer seal construction

Pros:

  • Ceramic does not age or fatigue (long-term stability)
  • Minimal temperature influence on the ceramic material and measurement
  • High chemical resistance
  • Counter electrode (base) supports the diaphragm in case of over pressure
  • Easy to troubleshoot – crack in the diaphragm results in a positive offset (20 – 35% of measuring range)

Cons:

  • Elastomer sealing is necessary -  for gases only below 25 bar / 363 psi; quickly decreasing pressure can lead to mechanical failure of the seal due to its permeability
  • Support of the measuring cell is necessary; this leads to added cost

Stainless steel strain gauge measuring cell

Strain gauges are attached to the stainless steel measuring cell. Pressure of the medium on the measuring cell causes deflection of the strain gauges, which creates a change in resistance. Tension (positive strain) increases resistance and compression (negative strain) decreases resistance. The change in resistance is proportional to the pressure applied.

Features:

  • Pressure ranges from 6 bar (87 psi) to 600 bar (8700 psi)
  • Suitable for gas up to 600 bar (8700 psi)

Pros:

  • No elastomer seal required
  • High burst strength at high ranges
  • Fully welded all stainless steel diaphragm

Cons:

  • Lower over pressure and burst pressure limits at low ranges
  • Temperature compensation is necessary