Air flow measurement resolution is an essential element of HVAC controls.

Improve VAV/HVAC controller performance with cost effective MEMS mass flow sensors

Air flow measurement resolution is an essential element of HVAC controls. Accurately measuring the amount of fresh air intake is critical to ensuring good indoor air quality. New environmental control systems are challenging designers to accurately measure for very low flow rates allowing a reduction in HVAC duct noise. It is imperative that a flow sensor used in the system be able to distinguish between low flow, no flow and negative flow for these controls to work properly.

The Omron D6F-P series (Figure 1) was designed to address the challenges of this market’s applications. Figures 2 and 3 show the D6F-P installed on HVAC Control boards.

Figure 1: The Omron D6F-P series mass flow sensor.

HVAC controls, including Variable Air Volume (VAV) controllers typically use either flow sensors to measure flow rates directly or differential pressure sensors to indirectly measure air flow. Historically, differential pressure sensors have been the less expensive option. The economically priced Omron D6F-P MEMS Mass Flow Sensor, however delivers exceptional performance over pressure sensors (see video clip below). 

Measuring the mass flow rate directly compared to measuring differential pressure is illustrated in Figure 4. The shape of the curve of the mass flow sensor provides a very high level of resolution as the flow approaches zero.  Omron’s MEMS Mass Flow sensors can accurately measure down to 0.01% of their full scale. 

Figure 2: The Omron D6F-P0010A1 in an E.H. Price Silent Guard Heater Control Module. (photo courtesy of E.H. Price Limited).

This D6F-P flow sensor series utilizes MEMS technology delivering a number of other features making it superior to other sensors currently available. 

1. Based on industry feedback, this package was designed with the flow ports conveniently located on the same side of the unit to eliminate the potential problem of hose kinking due to one hose being routed around to the opposite side of the sensor.  The internal flow path of the sensor is nearly symmetrical, allowing the device to be use in bi-directional applications (contact the factory for bi-directional calibrations). 
2. It is available with either PCB terminals or a plug-in connector (a popular choice for easy prototyping). 
3. The D6F-P is a 1 LPM rated device, however, when used in a bypass set-up, it can be used to measure flow rates in excess of 200 LPM. 
4. To maintain accurate, repeatable results in particulate laden or “dusty” conditions, such as those found in HVAC applications, a patented Dust Segregation System (DSS) is incorporated in the D6F-P series (see video clip below). As the air enters the flow path from either direction, it is routed through a centrifugal chamber. The centrifugal action segregates the particles from the gas stream that passes over the sensing element. The DSS helps to maintain the sensor’s accuracy and reliability over a long life and often eliminates the need for an external filter saving money, space and assembly time.

If you cannot see the below You Tube video, click here.

Figure 3: The Omron D6F-P installed on a Price Intelligent Controller VAV Expansion Module (photo courtesy of E.H. Price Limited).

The innovative features found in Omron’s new D6F-P were recognized in June of 2008 as it received the Silver “Best of Sensors Expo” award in the Sensors category.  

Figure 4: This chart illustrates the superior signal resolution exhibited by the MEMS mass flow sensors over differential pressure sensors, at very low flow rates.

If your application requires a flow sensor that is able to distinguish between low flow, no flow and negative flow, contact Omron and ask about their D6F-P series. They have a complete set of technical data, qualified application assistance, technical support and engineering samples