Pressure Sensors and Transmitters for HVAC and Air Handling Applications

Closed Loop Control adds capabilities to set and maintain flow rates via pressure management by directly controlling motors, valves and actuators. Superior Sensors offers the option to have this capability integrated into the sensor in order to more effectively set and maintain flow rates by directly controlling motors, valves and actuators to maintain flow rate targets.

The integrated Closed Loop Control design significantly reduces loop delays in the electronic circuit by up to 100x. This integrated solution also eliminates the need to design and implement a complex control loop system, resulting in more efficient, more reliable and less costly products. Closed Loop Control is of extreme value in medical respiratory devices such as ventilators and CPAP, as well as in air quality measurement products.

The figure below shows a block diagram of an implementation of the Superior Sensor Closed Loop Control for an air quality application. In order to effectively measure the air quality, we require maintaining a constant/known airflow through the viewing window. The differential pressure across the venturi directly measures the flow into this viewing window. The system sets a target pressure level across the venturi and the differential pressure sensor automatically increases or decreases the drive to the pump to maintain the targeted differential pressure, ensuring a constant airflow into the viewing window. This is accomplished with the NimbleSense closed loop circuit used in combination with the company’s proprietary noise filtering, resulting in greater than 100x reduction in loop delay.

Superior Sensor’s advanced digital filter is a multi-order filter that utilizes advanced filtering capabilities on the front-end of the sub-system to eliminate critical noise created by fans, blowers or other dry air/gas sources prior to reaching the pressure sensing sub-system. The NimbleSense advanced filtering capability removes sensor induced mechanical noise before it becomes an error signal that can adversely impact overall system performance. In customer deployments where our sensor replaced a competing component, we have seen greater than 10x reduction in sensor induced noise, thus greatly improving the SNR of the sensor output. In very low pressure systems, the improvement is even more significant.

Incorporating both standard and optional digital filters, this feature provides significantly better noise reduction and eliminates the need to design an external filtering system, resulting in more efficient, more reliable and less costly products. Our advanced digital filtering is optimized for each application to ensure mixed sampling noise is kept well below the noise floor. By removing the mechanical noise, we maximize overall system performance.

The example below is of a 4th order FIR filter customized to block pump noise above 50 Hz, which has noise of equal magnitude as the signal of interest. The lower graphs show the resulting impact of the advanced digital filtering.

As all of Superior’s pressure sensors have an extremely low noise floor, theoretically power line interference can be ‘heard’ when taking measurements. The integrated 50Hz/60Hz notch filter eliminates this noise so you maintain the advantage of having such a low noise floor pressure sensor without any external interference. With the notch filter seamlessly integrated in the pressure sensor module, the sensor blocks out the interference caused by these frequencies before it reaches the user application. Further, as the notch filter is internal to the sensor module, it eliminates the need for an engineer to design and implement an external notch filter. This feature removes an external notch filter, so the overall system is more efficient, more reliable and less costly.

Benefits of the integrated 50/60Hz Notch Filter include:

1. Eliminate the noise from the power grid and AC devices before it reaches the sensing element
2. Simplify product design with an integrated approach
3. Speed time to market by not having to design and/or implement an external notch filter
4. Lower overall system cost as an external notch filter is no longer required

A pressure switch is a mechanical or electronic device that is activated when a certain pressure threshold or set point is reached. These failsafe response components instruct the system to perform an action if a certain pressure threshold is met.

Types of Pressure Switches

Fixed Pressure Switches

As their name implies, fixed pressure switches have pre-set, non-changeable pressure thresholds that are set by the pressure switch manufacturer. The device maker receives the pressure switch already configured and cannot change values. Examples where fixed pressure switches are common are certain types of medical devices, such as ventilators.

Variable Pressure Switches

With variable pressure switches, the threshold value can be set either by the device maker or dynamically in the field. If it is controlled by the device maker, when they build their product they select certain resistor pairs that control the voltage input that determines the threshold. Once they build the product, the threshold value cannot be changed.

In cases where the threshold can be set in the field, this is typically done via software or a mechanical knob/switch. In this scenario, the pressure switch is usually not implemented as a safety feature. A good example is with air filters – where depending on the system implementation, the threshold value needs to be adjusted to account for any head loss in the flow stream.

Superior Sensor’s pressure switch changes state depending on the measured pressure being above or below a certain threshold. This can be used as a fast response failsafe feature for overpressure conditions, and to provide other simplified on/off system feedback. However, unlike other more common pressure switches, the Superior Sensor pressure switch includes three modes for setting threshold pressure, one fixed and two variable:

• Fixed mode: Superior Sensor Technology sets the threshold and provides the ‘ready for use’ configured sensor (with integrated pressure switch) to the device manufacturer.
• Variable mode 1: The device manufacturer can configure and set the proper thresholds at the time of product manufacturing.
• Variable mode 2: Pressure thresholds are field programmable via software, so the pressure switch can be ‘tuned’ after product manufacture depending on the use case.

Benefits of Superior’s integrated pressure switch include:

1. Flexibility with 3 modes of operation
2. Lower system cost as need for an external pressure switch is eliminated
3. Smaller overall PCB footprint
4. Improve the reliability of your product by eliminating external components
5. Minimize system power and heat
6. Simplify your product design
7. Speed your time to market