Integrated Closed Loop: When Time, Money and Accuracy Matter

Effective Pressure Sensor Implementations Require an Accurate Closed Loop

A closed-loop control system automatically regulates a process to a desired state based on continuous feedback from the system. It contains one or more mechanical or electronic devices adjusted based on feedback of the current state to potentially adjust the system to reach the desired state. In many devices, closed-loop systems, sometimes known as feedback control systems, are designed to automatically achieve and maintain the desired state without any human interaction.

Figure 1:  Basic Control Loop System

Pressure sensors are often used to measure pressure or flow in systems. Sensor output is often directly used as feedback in a closed-loop system. Differential pressure sensors measure the flow, level, or density of air and gas. They are frequently the key feedback component of many important systems in the medical, industrial, aviation, automotive, energy, and HVAC fields.

While many systems use the pressure sensor as the center of a control loop feedback system, they often employ software as the external control mechanism. However, utilizing software requires a higher speed that draws more power. In addition, there is a need for added hardware, and the system is beholden to injected system noise that impacts sensor performance. To minimize the noise, the sensor is typically run at a higher speed as well. There are several drawbacks to this kind of implementation:

1. Cost: the additional components add to the bill of materials (BOM) of a product
2. Accuracy/Timing: the more complex the feedback loop, the longer the loop takes to complete resulting in a greater time lag, ultimately impacting accuracy
3. Design Complexity: the overall product design is more complex and takes more time to develop
4. Reliability: the more components in a product, the greater the number of possible failure points
5. CPU Requirements: to run the system requires a higher-end, faster CPU that consumes more power and generates more heat

The NimbleSense^TM Closed Loop Control Capability

Superior Sensor Technology's proprietary NimbleSense architecture, incorporated into all our differential pressure sensors, combines processing intelligence with signal path integration and intelligent 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 a closed-loop controller, enabling the company to incorporate this function directly into certain sensor products. This optional capability eliminates the need to design and implement a complex control loop system, resulting in more efficient, reliable, and less costly products.

Superior Sensor’s CLC adds the control capability to set and maintain flow rates via pressure measurement in the sensor. It can control motors, valves, and actuators to maintain flow rate targets. In addition, NimbleSense runs at a very high speed with advanced filtering capability that removes sensor-induced mechanical noise before it becomes an error signal that can adversely impact overall system performance. The integrated CLC design significantly reduces loop delays in the electronic circuit by up to 100x.  

Figure 2:  Closed Loop Control – Air Quality Application Example

Figure 2 shows a block diagram of an implementation of the Superior Sensor CLC for an air quality application. 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 and the company’s proprietary noise filtering (topic for another blog post), resulting in a greater than 100x reduction in loop delay.

Summary of Benefits

The NimbleSense CLC capability can benefit many products, including, but not limited to, ventilators, sleep apnea machines (CPAP, BiPAP), oxygen concentrators, anesthesia machines, flow meters, and HVAC systems.

To summarize the benefits of the NimbleSense integrated Closed Loop Control capability:

1. Greatly reduce loop delays to improve the accuracy and responsiveness of your product
2. Improve the reliability of your product by eliminating discrete parts
3. Reduce your overall system costs
4. Minimize system power and heat
5. Simplify your product design
6. Speed your time to market

If you have an application that requires closed-loop control, please contact us so we can discuss how best to implement the NimbleSense CLC capability into your product, leveraging the benefits listed above.