Can’t Take the Pressure? Integrate a Pressure Switch

The Importance of Pressure Switches

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. Pressure switches can be deployed to ensure there is enough flow going through the system (e.g., enough air flowing through an air filter). They can also be implemented to ensure there is not too much pressure applied to the patient (e.g., a ventilator delivering air to a patient’s lungs).

Traditionally, these switches have been mechanical in nature; however, advancements in technology are starting to phase them out in favor of electronic controls. There are several reasons for the shift to electronic pressure switches, including:

• Faster adjustments, resulting in better response time and greater accuracy
• Field programmability
• Better usability and more ‘plug and play’ setup
• Higher reliability and easier to service
• Greater operating flexibility

Figure 1 – Mechanical vs. Electronic Pressure Switch

Pressure switches are used in many applications. With regards to air and gases, some of the more common devices that incorporate pressure switches within the medical and HVAC markets are:

1. Medical ventilators: ventilators use pressure switches to significantly reduce patient hazards, by generating alarms (or shutting down systems) if too much pressure is being applied to the patient. 
2. Positive Airway Pressure Devices: CPAP, BiPAP, and APAP devices are used to treat many respiratory conditions, including sleep apnea, COPD, and asthma. Like with ventilators, pressure switches are utilized to significantly reduce patient hazards if too much or too little air pressure is being applied to the patient.
3. Oxygen Concentrators: Oxygen concentrators reduce the nitrogen level in the air and increase the oxygen level. Pressure switches generate warnings in the event of error or overpressure.
4. Air filtration: air filtration systems block dust and other particles from being pumped into the air. A pressure switch can act as an alarm to alert technicians that it is time to clean or replace a dirty filter because the airflow pressure drops below a certain threshold.
5. Airconditioning vents: Air vents are the endpoints throughout an ‘airflow network’ where air reaches the room it is trying to cool or warm. Pressure switches can be installed within the vents to generate an alarm if the vent is starting to clog.

Types of Pressure Switches

With regards to electronic pressure switches, there are both fixed and variable types.

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.

The NimbleSense^TM Pressure Switch

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 a pressure switch capability that is integrated directly into the pressure sensor.

Like other pressure switches, 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.

The three modes provide the manufacturer with full implementation flexibility. Moreover, as an integrated part of the pressure sensor, the Superior Sensor pressure switch does not require the addition of an external switch, so it:

• eliminates the cost of an external pressure switch
• reduces product PCB space requirements
• lowers system-level power consumption

System Benefits

The NimbleSense pressure switch capability can benefit all electromechanical products, including HVAC systems, medical ventilators, CPAP/BiPAP/APAP machines, oxygen concentrators, anesthesia machines, and various industrial devices.

At the systems level, the NimbleSense pressure switch provides several benefits:

1. Simplifies product design with an integrated approach.
2. Speeds time to market by not having to design-in an external pressure switch.
3. Reduces system costs by eliminating the need for additional components.
4. Provides maximum design flexibility due to its three modes for setting threshold pressure.

Availability

Superior Sensor’s pressure switch capability is available with the following product lines:

• CP Series
• HV Series
• ND Series
• VN Series
• Custom products