Electromechanical devices, such as HVAC systems, hospital ventilators and monitoring systems, are comprised of many parts that generate noise when these parts move, or the systems have air/gas/liquids flow through them. Unfortunately, when this noise is superimposed on the signal to be measured it can have a major impact on the product’s accuracy and performance.
Noise filtering is the process of removing noise from a signal. The more noise that can be removed, the more accurate a system will perform. This is easily observed in audio and video systems. In audio, the elimination of noise leads to a clearer, hi-fidelity sound. While in video, noise is the culprit behind any blurriness, ghosting and judder of a video stream.
A common term used to measure signal quality is signal-to-noise ratio, or SNR for short. This measure takes the strength of a signal and divides it by the noise level. For example, in audio you take the signal level divided by the noise level generated by the audio equipment and express this value in decibels (dB). The higher the SNR, the better the audio quality.
The lower the overall signal strength, the greater effect noise will have on the system. If you are measuring radioactivity or chemicals in the air, for example, all it takes is a very low level of gas to create a toxic environment. The measurement device must be capable of filtering out all system noise to ensure an accurate reading. Being off by just a little can have a significant impact on the health of those in the area.
With regard to HVAC, industrial and medical devices, many components generate noise including fans, air blowers and motors. When pressure sensors are involved, especially differential pressure sensors, every small reduction in noise can have a significant impact on the accuracy of the reading. If you are measuring the levels of poisonous gas in a facility, air pressure levels in aviation or patient air flow through a respirator, just a small amount of system noise can have a major impact.
The NimbleSense Advanced Digital Filtering Capability
Incorporated into all our differential pressure sensors, Superior Sensor Technology’s NimbleSense architecture is a fully integrated sub-system that combines processing intelligence with signal path integration and proprietary algorithms to create modular building blocks that are easily selectable to support a wide array of applications. One of the building block components in NimbleSense is an advanced digital filtering capability. With 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.
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. Especially with very low pressure systems, the improvement is even more significant.
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.
Figure 1: 4th Order FIR Filter Blocking Pump Noise above 50 Hz
Figure 2: Before & After Results from NimbleSense 4th Order FIR Filter
Summary of Benefits
The NimbleSense advanced digital filtering capability can be beneficial for all electromechanical products including ventilators, sleep apnea machines (CPAP, BiPAP), oxygen concentrators, anesthesia machines, industrial devices and HVAC systems.
To summarize the benefits of the NimbleSense integrated advanced digital filter capability:
- Greatly reduce system noise levels by 10X or more, especially important in very low pressure applications. For noise prone systems, an improvement of 100X to 1000X is not unreasonable.
- Eliminate noise sources such as fans and blowers before they reach the pressure sensing sub-system.
- Simplify your product design with an integrated approach.
Speed your time to market by not having to design an external filtering system
