Technology Focus: Pressure Measurement in Medical Applications

Guidance: Medical device designers must consider the thorny problem of condensing humidity when choosing a pressure sensor. Often, they need to weigh the trade-offs between feature features, package types, and costs. In addition to this, in addition to the bulky heavy-duty media isolation pressure sensor, there are few other sensing options available for medical devices. This pressure sensor was once the only choice before the introduction of a board-mounted sensor compatible with liquid media.

For applications with medium to low pressure requirements, including gas/liquid chromatographs, chemical analyzers, ventilators and blood analyzers and diagnostic equipment, pressure sensors must not only be in direct contact with liquid media or withstand humid conditions, but also It also provides highly accurate pressure measurements for a variety of media such as exhaled gases, reagents, samples, and cleaning solutions. Board-mounted pressure sensors are often the solution of choice for applications with pressure ranges below 150 psi and in tight spaces, and they are available in terms of functionality, package size, reliability and cost.

To get the most accurate pressure readings, the sensor should be as close as possible to the medium to be tested. However, not all pressure sensors are compatible with liquid media, which poses a major problem for medical device designers. In many cases, they need to design additional components such as bypass or filters to solve the humidity problem, or to rethink the positioning of the components, especially in the system to avoid any fluid contact with the sensor. These tasks require additional design time and cost.

Anti-liquid, moisture-proof

Now, sensor manufacturers have developed board-mounted sensors. These sensors not only isolate liquid media and highly humid environments, they are suitable for medical devices with low to medium pressure measurement requirements, but also eliminate the need for designers to design additional protection features or redesign products (ensuring that fluids do not come into contact with the sensor), so Simplified design.


Image caption: Honeywell's TruStability pressure sensor offers a wide range of configuration options, reducing design and development time.

In chemical analyzers, pressure sensors require highly accurate and repeatable measurements at low pressures and need to withstand higher pressures during flushing and cleaning.

For example, liquid media compatible board mounted pressure sensors are a good choice for chemical analyzers. Because chemical analyzers require accurate measurements of liquid flowing through the system in a repetitive manner. In general, in a chemical analyzer, a pipette is required to pump a sample liquid, and then the sample is dropped into a sample bottle for mixing or analysis. During this process, the pressure sensor not only ensures accurate pumping of the required sample, but also detects whether the pipette is clear or whether the pipette is properly placed in the vial.

Pressure sensors must have high precision measurements and repeatable operation requirements when measuring in low pressure environments. At the same time, they are also able to withstand the higher pressures caused by flushing or cleaning the fluid path. All of this is premised on direct contact with the liquid medium to be tested.

Examples of such sensors include the 24PC/26PC board-mounted pressure sensors from Honeywell Sensing and Control, which detect small pressure changes between readings and accurately measure the flow through the system in a repeatable manner. Specific liquid flow ensures that the liquid has flow and flow rate data (this is the core point for the operation of the analytical equipment). In addition to being used as a pressure sensor for single-sided contact with liquid media, the differential sensor is also a unique solution for liquid media compatible with liquid media.

Multiple options

Honeywell's TruStability pressure sensor family offers a wide range of configuration options that dramatically reduce design and development time.

In ventilator applications, a board-mounted pressure sensor is used to measure the airflow inhaled and exhaled by the patient. To ensure that the air and oxygen pressures do not exceed the values ​​set by the healthcare provider, the sensor needs to be highly stable and highly accurate. Honeywell's TruStabilityHSC/SSC pressure sensors are extremely rigorous and can detect pressures as low as 250Pa (1 inch water column), making them perfect for ventilator applications. In addition, these sensors support I2C or SPI digital outputs that interface directly with a microprocessor or microcontroller, simplifying design and improving system performance.

The TruStability sensor has a liquid media option and is therefore suitable for applications that come into direct contact with liquid media or condensation environments. These options are a key consideration when placing the sensor close to the patient, especially in the expiratory portion of the ventilator, which must withstand the high humidity air caused by the patient's cough and exhalation.

The emergence of 24PC/26PC and TruStabilityHSC/SSC pressure sensors solves the problem of designers of chemical analyzers, ventilators or other similar types of medical devices who want to position the pressure sensor as close as possible to a fluid or humid environment. Design ideas for accurate pressure readings. These sensors are designed to withstand a wide range of non-corrosive, deionizing liquid or gaseous environments and offer a wide range of options such as pressure range, package type and digital/analog output range for maximum flexibility in medical device design. .

Because many medical device applications are likely to come into contact with fluids and gases, designers should always prioritize pressure sensors with liquid media compatibility to simplify design. In addition, they need to understand the type of fluid the pressure sensor can contact to ensure it is compatible with the fluid.

Designers should also consider pressure sensors with full compensation, amplification, and calibration features to make operation easier. Thanks to these sensors, signal conditioning components can be avoided on printed circuit boards, which can save space, increase reliability, reduce costs, and simplify.

Matching requirements between sensors and applications

Of course, in any case, the best choice should be determined first according to the application. For example, in applications such as alarm circuits, designers may prefer low-cost pressure sensors that are compatible with liquid media and have no amplification and compensation characteristics.

At the same time, look for pressure sensors that are easy to integrate into your design. This means that the device should offer a variety of port types, packages, and output types (analog and digital) options. In addition, pre-inspection of sensors is also a major advantage in accelerating development and production cycles.

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