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 analog signal is then converted into a digital pressure by the sensor’s microprocessor.
Note the signal change as pressure is applied to the sensor in the animation below.
The strength of the ceramic capacitive measuring cell comes from the overall design of the process connection and measuring cell. The ceramic itself it very hard, and the ceramic diaphragm is supported by the ceramic base in case of overpressure. The complete measuring cell is also centered and supported by a brass locating ring behind the body of the ceramic cell. The measuring cell is placed in the bottom of the process connection and then the locating ring is threaded into place creating a very robust support system. This is how we can achieve very high-pressure ratings. Alternatively, a stainless steel diaphragm is supported by the fill fluid, but this is not a rigid or robust system.
All relative pressure, often referred to as gauge pressure, measurements require a reference to atmospheric pressure or the surrounding ambient environment. The pressure measurement is a differential between atmospheric and system pressure, therefore “relative” to atmospheric pressure. To accomplish this most pressure sensors use some sort of vent system, which opens the measuring cell to atmosphere, so the system pressure is measured above or below (vacuum) this reference.
ifm has optimized the location and design of the atmospheric vent to improve machine availability and process performance.
The vent is located 90° from the display to optimize vent orientation while keeping the display in a preferred position
Optimizing the vent orientation (keeping the membrane vertical) allows the Gore-Tex membrane to shed moisture, which prevents clogging and reduces measurement errors due to incorrect reference pressure.
ifm rigorously tested design variations to improve cleanability, breathability, and flow of media though the vent.
Everything from the amount and size of holes to improve flow through the vent to the drip edge which prevents media from entering the vent were considered. This prevents build-up in the vent which can cause measurement offsets and increases machine performance.