In HVAC systems, the ability to monitor volumetric flow rates and pressures in lines and rooms is decisive when it comes to operating heating, ventilation, and air-conditioning systems efficiently and economically. Pressure sensors are a central element for controlling the systems. To ensure compliance with strict legal requirements and to minimize energy costs, ever-decreasing measuring ranges as well as greater measuring sensitivities, accuracies, and long-term stabilities of the sensors are required. In addition, the pressure sensors must cope with particular requirements in HVAC systems, such as dust-laden air, and must be small and easy to integrate in OEM systems.
Differential pressure sensors measure the pressure drop across a flow element, such as an orifice or a measuring cross, as a measure for the volumetric flow rate. The sensor is located in a bypass to the main flow line. In volumetric flow controllers for variable volumetric flow (VAV), the pressure measurement is used to control the damper position within a closed control circuit and enables demand-controlled ventilation. Pressure sensors are an important component of these systems and play a key role in the quality of control.
The opening and closing of ventilation dampers to individual rooms results in pressure changes in the ventilation ducts. The fan in the ventilation system is controlled based on demand so that constant channel pressure is guaranteed at all times to provide efficient ventilation and air conditioning. A pressure sensor monitors the channel pressure and is used to control the fan power. In this way, it contributes significantly to the safety and economic efficiency of the system.
In air-conditioned rooms, the supply and extraction of air should be controlled in a manner that minimizes differential pressures between individual zones or relative to the surrounding environment. In clean rooms, on the other hand, a constant overpressure must be guaranteed to prevent the entry of untreated air. In laboratory rooms and hospitals, a constant negative pressure is used to prevent the spread of germs and hazardous substances. In all applications, precision pressure sensors monitor the very low differential pressures, thus enabling safety and comfort.
Contaminated air filters increase the pressure loss in ventilation channels and systems, which requires more fan power and increases energy costs. Electronic filter monitoring with an integrated differential pressure sensor measures the pressure drop over the filter and promptly triggers a message to replace the filter. Sensitive pressure sensors therefore play an important role in the economical operation of ventilation and air-conditioning systems. Differential pressure monitoring also enables defects such as a torn filter to be detected.
First Sensor offers a range of sensor technologies for measuring minute differential pressures in HVAC systems - flow-based differential pressure sensors and membrane-based piezoresistive silicon pressure sensors 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 which is conducted through a very small flow channel 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, the sensors are highly resistant to dust, humidity, and long connection tubes compared with conventional flow-based pressure sensors.
First Sensor membrane-based piezoresistive pressure sensors from the 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.
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