Efficiently operating differential pressure sensors, controllers and switches are essential for achieving good air quality that every reliable HVAC system should create. Effective ventilation relies on maintaining the correct level of differential pressure throughout the system. Insufficient pressure differentials can lead to issues such as inadequate airflow, which compromises indoor air quality and comfort. Conversely, excessive differentials may strain components and increase energy consumption.
The term "differential pressure" denotes the pressure variance between two distinct locations. Various industries utilise differential pressure sensors to gauge this particular form of pressure.
What is a differential pressure switch?
Differential pressure switches detect disparities in pressure between these two specified points. These switches feature two ports linked to the respective pressure sources, thereby monitoring the differential pressure between them. Upon reaching a predefined threshold, the internal diaphragm within the switch deflects to establish or interrupt a circuit connection. This alteration in the circuit triggers an alarm, notifying users of the pressure shift. Users can either preset the switching point or adjust it on-site.
Differential pressure switches detect disparities in pressure between these two specified points. These switches feature two ports linked to the respective pressure sources, thereby monitoring the differential pressure between them. Upon reaching a predefined threshold, the internal diaphragm within the switch deflects to establish or interrupt a circuit connection. This alteration in the circuit triggers an alarm, notifying users of the pressure shift. Users can either preset the switching point or adjust it on-site.
What is a differential pressure sensor? 
Differential pressure sensors, also known as transmitters or transducers, are devices designed to measure the disparity between two absolute pressures. They can be used for filter monitoring, cleanroom ventilation, etc.
The operational principle of a differential pressure transducer involves two hermetically sealed chambers, each equipped with a process connection. These chambers are separated by a flexible membrane, affixed with a resistance bridge. The process connections are positioned before and after any potential pressure reduction, ensuring that the pressures exert opposite forces on the membrane.
Under equal pressure conditions in both chambers, the membrane remains flat. However, when there is a variation in pressure within one of the chambers, the membrane deflects towards the chamber with the lower pressure. The extent of this deformation corresponds to the difference between the two pressures. This deformation induces a change in the resistance value of the bridge, which can then be converted into an electrical signal (transmitted by the sensor analogue output) for subsequent processing by an EC fan or AC fan speed controller.
Differential pressure sensors, also known as transmitters or transducers, are devices designed to measure the disparity between two absolute pressures. They can be used for filter monitoring, cleanroom ventilation, etc.
The operational principle of a differential pressure transducer involves two hermetically sealed chambers, each equipped with a process connection. These chambers are separated by a flexible membrane, affixed with a resistance bridge. The process connections are positioned before and after any potential pressure reduction, ensuring that the pressures exert opposite forces on the membrane.
Under equal pressure conditions in both chambers, the membrane remains flat. However, when there is a variation in pressure within one of the chambers, the membrane deflects towards the chamber with the lower pressure. The extent of this deformation corresponds to the difference between the two pressures. This deformation induces a change in the resistance value of the bridge, which can then be converted into an electrical signal (transmitted by the sensor analogue output) for subsequent processing by an EC fan or AC fan speed controller.
There are two primary methods of measurement for Sentera’s low-resolution sensor types: piezoresistive and capacitive. The majority of differential pressure sensors utilize the piezoresistive effect, wherein the electrical resistance of a material changes under tension or pressure. All piezoresistive sensors exhibit minimal drift. On the other hand, capacitive transmitters for differential pressure feature a capacitor embedded within a silicon chip. Changes in capacitance provide insights into the resulting pressure difference.
Sentera’s most recent high-resolution sensor series feature a digital, low pressure MEMS sensor element (micro-electromechanical system) offering state-of-the-art pressure transducer technology and CMOS (complementary metal–oxide–semiconductor) mixed signal processing technology to produce a digital, fully conditioned, multi-order pressure and temperature compensated sensor with a dual vertical porting option.
Sentera’s most recent high-resolution sensor series feature a digital, low pressure MEMS sensor element (micro-electromechanical system) offering state-of-the-art pressure transducer technology and CMOS (complementary metal–oxide–semiconductor) mixed signal processing technology to produce a digital, fully conditioned, multi-order pressure and temperature compensated sensor with a dual vertical porting option.
What is a differential pressure controller?
A sensor controller offers the possibility to define a setpoint for a single parameter. This setpoint is the greatest difference between this type of devices and the others. Instead of a range of values, only one point is acceptable for the sensor controller. This category contains only the Sentera's sensor controllers that measure differential pressure, volume flow and air velocity. It is a separate category because it does not have a proportional output, but a PI algorithm. PI stands for Proportional Integral. It is a control loop that continually calculates a correction between a setpoint and the actual measurement.
The PI algorithm controls the analogue output. The PI algorithm ensures that the controlled parameter retains its setpoint value.
For example: the differential pressure controller controls the 0-10 Volt output to maintain the differential pressure at the requested setpoint.
Sentera’s differential pressure sensors, switches and controllers are used to measure and control low differential pressures of non-aggressive and non-combustible gases, but they have been especially developed for air. The selectable analogue / modulating output signal has different meaning, depending on the setting of the device. If the device is used as a pressure sensor, the output signal is proportional to the measured pressure. As a volume flow sensor, the device calculates the process flow using differential pressure readings. In air velocity control, the output signal represents a manipulated variable of the PI control.
Depending on the connected differential pressure accessories, the devices can measure and/or monitor and control different parameters. Based on this measurement, air volume flow [m³/h] or air velocity [m/s] can be calculated. To calculate air volume flow based on the K-factor of the fan, use the connection set type PSET-PVC-200 or PSET-QF-200. This optional connection set can also be used to measure differential pressure. To calculate air volume flow based on the duct cross section [cm²] or air velocity [m/s], use the optional connection set type PSET-PTS-200 or PSET-PTL-200.
What is an air filter monitoring device? An air filter monitoring device is a piece of equipment used in HVAC systems to monitor the condition and efficiency of air filters. These devices typically employ sensors or detectors to assess factors such as airflow, pressure differentials, particle concentration, or filter resistance. By continuously monitoring these parameters, the device can indicate when filters need replacement or maintenance. This helps ensure that air filters are changed at the appropriate intervals, maximizing system performance, indoor air quality, and energy efficiency.
Sentera’s FIM series of filter monitoring devices, offers options to monitor either one or two air filters simultaneously. The series can be used for monitoring pressure drops. Air filters impede airflow, creating resistance. As dust and particles accumulate, this resistance increases, causing a higher pressure drop across the filter. The monitoring device measures this pressure drop, indicating filter condition. If it surpasses a set threshold, it signals the need for maintenance.
Also, the FIM series can send real-time data and alerts, allowing continuous monitoring by operators or maintenance staff. Notifications or alarms are triggered when filters require attention, facilitating prompt maintenance actions. Alerts are delivered via SMS or email.
These devices record and store data on filter performance, pressure drop trends, and other relevant parameters. Analysis of this data enables identification of patterns, optimization of maintenance schedules, and detection of potential filtration system issues.
What is more, to facilitate the last two features, the FIM can be connected to SenteraWeb, our online HVAC portal, thanks to the integrated Sentera Internet Gateway.
Significance of differential pressure sensing devices
Differential pressure measuring and controlling devices are integral to HVAC systems for assessing flow rates and pressures within air ducts and enclosed spaces. They facilitate the efficient and cost-effective operation of the systems. Pressure sensors serve as the cornerstone for HVAC system regulation, particularly crucial amid evolving stringent regulatory standards to ensure minimal energy consumption.
Moreover, differential pressure sensors contribute to enhanced comfort and, in certain scenarios, heightened safety within environments by monitoring key HVAC system parameters.
Key monitoring elements in HVAC Systems
Volume: Differential pressure sensors regulate air volume flow, enabling precise control over damper positions and facilitating demand-controlled ventilation.
Duct Pressure: Differential pressure sensors monitor pressure differentials in ventilation ducts, allowing for modulation of fan power to maintain consistent airflow.
Room Pressure: In addition to maintaining uniform pressure levels within standard air-conditioned spaces, differential pressure sensors are vital for specialized environments like cleanrooms, hospitals and laboratories to ensure appropriate pressure differentials for contamination control.
Filter Maintenance: Differential pressure sensors monitor filter condition by detecting pressure drops, prompting timely replacement notifications and even identifying torn filters.