In this section AMSYS explains some of the terms used in sensor technology and by AMSYS.
Question: What is a pressure sensor?
Answer: Pressure sensors are measuring devices which convert a physical quantity (pressure) into an electrical signal according to a selected measurement method. The respective applications and accordingly also the requirements for the pressure sensor vary: Size of the sensor, installation conditions, application-specific standards, technical requirements and the properties of the medium must be taken into account when choosing the pressure sensor.
Pressure sensors are used to monitor and control processes in applications ranging from medical technology to industrial technology.
Question: What is a differential pressure sensor?
Answer: With the help of differential pressure sensors two pressures are compared and a signal provided which is proportional to the difference in pressure. For more information, see:
Whitepaper “How to measure differential pressure using piezoresistive sensing elements”
Application note “Measuring over – and underpressure bidrectionally with one sensor”
Question: What is a barometric pressure sensor?
Answer: Barometric pressure sensors are used to measure atmospheric pressure. The ambient pressure is measured against a vacuum in the sensing element. Barometric pressure sensors are actually absolute pressure sensors which are calibrated for the special 700–1,200 mbar range. Barometric sensors can also be used to determine atmospheric altitude (altimeters).
Question: What is an absolute pressure sensor?
Answer: Absolute pressure sensors are used to measure pressure against a referential pressure of 0 bar (vacuum). This enables the pressure in an enclosed system to be determined regardless of the atmospheric pressure, for example.
The whitepaper “How to measure absolute pressure using piezoresistive sensing elements” explains the basics of absolute pressure measuring.
Question: How is the fill level in liquids measured by pressure sensors?
Answer: In level sensing the fill level or height of a liquid is measured in a container. The application note “Precise level sensing with a low pressure transmitter” describes how the hydrostatic pressure can be measured using a pressure sensor.
Question: Media resistance – how can silicon sensors be protected against liquid media?
Answer: Pressure sensors with silicon sensing elements are sensitive to liquids and a number of aggressive media. The application note “Media compatibility of silicon pressure sensors” describes which preventive measures can be taken to drastically reduce the dreaded media sensitivity of relative and differential pressure sensors, taking AMS5812 as an example.
Question: What is a relative pressure sensor?
Answer: Relative pressure sensors are used to compare a pressure with the ambient pressure, producing a signal which is proportional to the difference in pressure.
Question: What is a ratiometric sensor?
Answer: A ratiometric sensor is a sensor whose output signal reacts synchronously to changes in the supply voltage. Find more information about ratiometric sensors in application note “Ratiometry in pressure sensors” on the example of AMS 5812.
Question: How is altitude measured by an absolute pressure sensor?
Answer: The geographical altitude can be calculated by taking the atmospheric pressure and applying this to the barometric formula. The atmospheric pressure can be easily determined by an absolute pressure sensor which is calibrated to the barometric pressure range. To define the altitude the atmospheric pressure is measured at the starting point and the measurement position. The difference in pressure is entered in the barometric formula which then gives the difference in altitude between the initial position and point of measurement. Find more information in application note “Precise altitude measurement with pressure sensors” on the example of the absolute pressure sensor MS5611.
Question: What is a bidirectional differential pressure sensor?
Answer: In pressure sensing technology several terms have become established which describe the various methods of measurement (including absolute, relative and differential pressure sensing). Bidirectional differential pressure sensors measure the difference between two measurement pressures; this difference can be either positive or negative. This means that a bidirectional differential pressure sensor measures both positive and negative pressure. For more information, see:
Application notes “What to know about bidirectional differential pressure sensing” and “Measuring over – and underpressure bidrectionally with one sensor”
Question: What is underside pressurization?
Answer: Each membrane on a pressure sensor has two sides. For the purpose of substrate bonding the upper membrane surface of the silicon sensing element has several small metal surfaces (bonding pads) made of refined aluminum that are not corrosion resistant. The pressure encumbered by media is therefore applied to the non-sensitive underside of the sensing element in an inverse process. For more information, see:
Application note “media compatible pressure transmitter for industrial applications in matchbox format”
Question: What is system pressure?
Answer: The ambient pressure the system is subjected to. If, for example, a filter is to be monitored by a differential pressure sensor in the millibar range yet the static pressure in the pipe housing the sensor has already reached 10 bar, a sensor or transmitter is needed which can withstand the high pressure of the ambient air. The system pressure is the maximum pressure which can be simultaneously applied at both pressure inputs of a pressure sensor versus the external pressure without the sensor being damaged. For more information, see:
Application note “Differential pressure transmitters for high system pressures”
Question: What is a transmitter / transducer?
Answer: Transmitters or transducers are calibrated, amplified, ready-to-use sensors with a standardized output in a package for direct installation. They are also simply known as ready-to-use sensors as they do not need to be soldered or assembled before being inserted in a system. These sensors are powered by a cable and short circuit protected.
Question: What is an OEM sensor?
Answer: Unlike transmitters OEM or original equipment manufacturer sensors are components which still have to be installed in a superordinate system, for example by being soldered onto a printed circuit board. They may have already been calibrated, compensated and amplified or not.
Question: What is a PCB module?
Answer: AMSYS PCB or printed circuit board modules are OEM sensors mounted on printed circuit boards with additional electronics which measure physical variables with an industrial, standardized supply and output voltage. They are short circuit protected but, as opposed to a transmitter, not packaged.
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