pressure differential – All Sensors | Put the Pressure on Us

The Pressure in Tornadoes

Welcome to All Sensors “Put the Pressure on Us” blog. This blog brings out pressure sensor aspects in a variety of applications inspired by headlines, consumer and industry requirements, market research, government activities, and you.

The Pressure in Tornadoes

The pressure inside a tornado is less than the surrounding atmospheric pressure. That pressure differential causes flow into the tornado of objects such as cars, mobile homes, other structures and more (reference Dorothy and Toto). Since tornadoes travel and are only in a specific location for a short time, getting a pressure measurement inside the tornado is quite difficult, so the database is quite small. However, according to the National Oceanic and Atmospheric Administration (NOAA) of the U.S. Department of Commerce, “A barometer can start dropping many hours or even days in advance of a tornado if there is low pressure on a broad scale moving into the area.” Of the measurements that have been made in the U.S., the lowest recorded pressure difference is 194 millibars. While it could be damaged like anything else sucked into a tornado, an All Sensors digital output ADO Series barometric pressure sensor could provide the measurement for indicating the pressure drop usually indicative of changing weather conditions.

This tornado formed during a large thunderstorm in Wyoming.
Source: National Center for Atmospheric Research (NCAR).

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Getting the Right Medical Room Pressure

Getting the Right Medical Room Pressure

With airborne infectious diseases that can easily spread from one person to another, such as the COVID-19 virus, isolation is critical. In a hospital or clinic, an isolation room needs negative pressure to have airflow into the room and avoid pathogens, or germs, from escaping. In addition to viruses, other undesirable contaminants to keep away from the rest of the population and sterile equipment in a hospital include bacteria, fungi, yeasts, molds, pollens, gases, volatile organic compounds (VOCs), small particles and chemicals.

The airflow to create and maintain the negative pressure (vacuum) in the room requires a consistent pressure differential of about 0.01 inch water gauge (in. w.g.) or 2.5 Pascals (Pa).

According to the Facility Guidelines Institute’s (FGI’s) most recent 2018 FGI Guidelines ANSI/ASHRAE/ASHE Standard 170-2017, other rooms that should be negatively pressurized include:

Emergency Department Public Waiting Areas
Emergency Department Decontamination
Radiology Waiting Rooms
Triage
Bathrooms
Airborne Infection Isolation (AII) Rooms
Most Laboratory Work Areas
Autopsy Rooms
Soiled Workrooms or Soiled Holding Rooms
Soiled or Decontamination Rooms in Sterile Processing Department
Soiled Linen Sorting and Storage
Janitors’ Closets

In contrast, protecting the patient and sterile medical and surgical supplies in an operating room requires positive pressure to keep undesirable contaminants outside. The positive pressure room is achieved by pumping in filtered, clean air.

Isolation (Low) vs. operating room (High) pressure.
Source: Minnesota Department of Health

In fact, some portable, headgear-mounted air purifying respirator systems use positive pressure to protect the wearer.

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Suction Solutions

Designers often look to nature for ideas that can be implemented in new products. Octopus suction cups provide an interesting pressure example.

When the octopus’ sucker is sealed to a surface, contraction of its radial muscles thins the wall of the sucker which tends to increase the enclosed volume. However, the cohesiveness of water resists volume expansion and the pressure of the enclosed water decreases instead. With this mechanism, an octopus can create a pressure differential of 100-200 kPa (14.5-29 psi) at sea level and generate a significant amount of force.

Suction cups allow professional glazers to easily pick up and move large pieces of glass. One company offers a Vacuum Cup Octopus with Pump that can lift a maximum weight of 185 kg (407.9 lbs.) vertically with a 300-mm (11.8-in) diameter vacuum cup. One version includes a manual vacuum pump with a leak gauge to monitor the effectiveness of the suction.

Source: Vacuum Cup Octopus with Pump

Vacuum suction cups offer a versatile method of material handling. In fact, suction cups also allow robots to pick different smooth surfaced objects. The approach has been applied to the robotics field since the 1960s. One recent research effort focuses on suction cups that can be used on robots designed to perform tasks in unstructured and contaminated environments. Of course, monitoring the amount of vacuum (negative pressure) with an accurate and rugged microelectromechanical systems (MEMS) pressure sensor can provide an even greater amount of control to more sophisticated suction applications.

Comments/Questions?
Do you have a pressure sensing question? Let us know and we’ll address it in an upcoming blog.
Email us at [email protected]