Air and gas flows as well as line and therapy pressures have to be monitored and controlled in numerous medical instruments such as respiratory devices, anesthetic devices, sleep diagnosis devices, sleep apnea therapy devices (CPAP), spirometers and oxygen concentrators. High-quality sensors in respiratory devices measure minute flow rates around the zero point of the respiratory flow and also detect flow rates of several hundred l/min. Applications in anesthetic devices call for sensors with high resistance to anesthetics. In controlled CPAP devices, pressure sensors continuously monitor the therapy pressure, thereby improving the comfort and quality of the treatment. Spirometers utilize special pneumotachographs that measure the respiratory flow using efficient differential pressure sensors.
First Sensor develops and manufactures highly reliable sensors and customized sensor systems as a strategic partner to medical product manufacturers in the area of breathing and respiration. Our complete advisory, development, production and service processes comply with the high requirements for medical products according to EN ISO 13485.
Volume flows in respiration can be measured directly with highly sensitive and rapid thermal mass flow sensors. The air or gas flow from a heating element located between temperature-sensitive resistors is heated slightly here. If the temperature profile in the medium is shifted by a mass flow, a flow-dependent voltage signal is generated via the temperature difference at the resistors.
First Sensor develops and manufactures customized thermal MEMS mass flow sensors within a modular technology platform. At the same time, we offer complete packaging technologies so as to realize complex integrated solutions from individual chip elements. First Sensor provides integrated analog or digital signal processing along with individual sensor calibrations and programming for all sensors. For the demanding requirements in respiratory devices, special solutions are available with very fast response times <2 ms as well as very high resolutions and, at the same time, large dynamic ranges for measurements up to 300 l/min. To this end, the sensor element can be located in the main flow or in a bypass channel. Customized flow sensors from First Sensor enable easy integration in end devices, cost savings during instrument development and competitive advantages thanks to short development cycles for you as a medical product manufacturer.
An indirect method for volume flow measurement involves measuring the pressure drop via a flow element. If respiratory air or gas flows through an artificial constriction in the flow line with a very low flow resistance, for example a screen or a laminar flow element, a minimal pressure drop results over the element, this representing a measure for the volume flow. These low differential pressures can be logged with highly accurate sensors and converted into an electrical signal. The differential pressure sensor is located in a bypass to the main flow line.
First Sensor offers a range of sensor systems for measuring minute differential pressures in medical technology – flow-based differential pressure sensors and piezoresistive pressure sensors with a very thin silicon membrane through which air does not flow.
Our flow-based LME and LDE differential pressure sensors operate according to the principle of thermal mass flow measurement of air through a very small flow channel that is integrated in the sensor chip. This innovative sensor technology enables highly sensitive measurement of ultra-low pressures from 25 Pa (0.25 mbar) full scale with ultra-high resolution and offset stability. Due to the minimal gas flow through the sensor, the LDE series is highly insensitive to dust, humidity, and long connection tubes compared with conventional flow-based pressure sensors.
First Sensor membrane-based piezoresistive pressure sensors in the HCL and HCLA series combine very high offset stability with low position sensitivity thanks to a special internal compensation technique. The silicon MEMS sensors achieve especially linear signal/pressure characteristic curves for pressure measuring ranges from 2.5 mbar full scale and offer analog and digital interfaces.