A pressure transmitter can be divided into two functional components:
– A sensor element that converts the pressure to an electronic signal.
– The transmitter electronics that amplify, convert, and apply signal conditioning such as linearization to the raw sensor signal.
The sensor element measures the pressure with strain gauge measuring technology, a thin sensor membrane will alter shape with the changes in pressure and that can be measured with a Wheatstone bridge on the membrane. A Wheatstone bridge is an electronic circuit whose electronic properties changes proportional to the altering shape of the sensor membrane, and this electronic change can be measured with extreme accuracy. Thus, the signal output from the sensor is proportional to the changes in pressure.
The sensor elements in Trafag’s pressure transmitters are mainly based on two different technologies: thin-film on steel and thick-film on ceramic. Piezoresistive sensors are also common on the market but only used by Trafag in special cases
Thin-film on steel sensors
A thin-film electronic circuit is sputtered onto a metal membrane, the membrane is only a few microns thick and acts as the strain gauge.
A pressure transmitter with thin-film on steel sensor has a completely welded design thus only two parts are in contact with the media, the sensor and the pressure connection. Our pressure transmitters have a stainless-steel sensor (1.4542/AISI 630) with excellent mechanical strength and corrosion resistance and the pressure connection and transmitter housing are available in different material. The design is reliable and leakage safe and no internal o-rings are used.
Thin-film on steel sensors are robust with excellent long-term stability and overpressure ratings, thus the pressure transmitter will not change its signal characteristics over time due to mechanical fatigue.
Advantages with thin-film on steel sensors:
Excellent long-term stability
Withstands high media temperature
Welded design, no internal o-rings
High overpressure (up to 5x nominal) and pressure ranges up to 3500 bar.
Thick-film on ceramic sensor
In this type av sensor is a thick-film electronic circuit printed onto a ceramic membrane. The measuring principle of a ceramic sensor is similar as a steel sensor, the printed circuit act as a strain gauge.
Ceramic sensors are an alternative to steel sensors for applications where steel sensors are not compatible such as highly corrosive or chemical media. As ceramic sensors can’t be welded an internal o-ring is used to seal the sensor and pressure connection. The choice of material in pressure connection and o-ring is adapted to the application requirements for chemical combability.
Advantages of ceramic sensors:
Chemical compatibility and corrosion resistance
Ideal for low pressures and absolute measurement
Electronics and ASIC
The pressure transmitters from Trafag are well known for high performance and reliability. The sensor element is an important part, but the pressure transmitter electronics are just as important. Trafag has developed an ASIC (Application Specific Integrated Circuit) specific for their pressure transmitters to ensure high quality signal conditioning and low noise.
The ASIC supports all sensor technologies (thin-film on steel, thick-film on ceramic and piezoresistive)
Wide operating temperature -40…125°C
Multi parameter signal conditioning with advanced 3d-mapping, for ex. temperature compensation