Barometric Pressure Sensors

What is the Model 278 with SETRACERAM?

The model 278 barometer is the ideal solution for measuring barometric pressure in remote environmental applications. The 278 is designed using the proprietary SETRACERAM™ ceramic sensor, enabling it to meet stringent accuracy requirements over wide operating temperatures in remote applications. The small footprint and removable terminal block on the 278 makes installation fast and easy. The 278 is ideal for solar powered applications because of its low power consumption and sleep mode feature. Under normal operation, this feature minimises current draw when readings are not being taken.

Designed for Remote Sensing Applications

The Model 278 pressure transducer is designed to be used in remote applications that require low power consumption. Its sleep mode feature allows for instant startup and fast readings.

Improved Performance with Ceramic Sensor

The 278 utilises a variable capacitance sensor that is made using ceramic material fused together with glass and gold to form the SETRACERAM™ pressure element. This stable material and design offers class leading thermal performance and low hysteresis, allowing it to be integrated into demanding installations. The ceramic sensor enables improved performance compared to other stainless steel sensors, enabling the 278 to give accurate measurements and better test results.

Flexibility in Installation

The Model 278 is designed with a compact footprint for quick installation. The removable terminal block provides easy wiring. Its mounting holes are designed to fit industry standard grid systems to maximize the use of panel space while minimizing your time at the job site.

Barometers in Automated Weather Stations

As a live example, the customer is an industry leader in measurement and control products for long-term barometric pressure monitoring. In this application, the Model 278 is used in a remote automated weather station. These types of weather stations forecast and monitor climate and boundary-layer meteorology. These stations are based around a programmable data logger that takes signals from various sensors, then processes, stores, and transmits the data. The data loggers have wide operating temperature ranges, on-board instructions, programmable execution intervals, and ample input channels for commonly used sensors.

Customer Problem

The customer has a demanding end user base which requires high end performance and superior service. Their main supplier limits their ability to perform on site calibration for their barometric pressure transducer needs. Lead time associated with sending products back for recalibration was lengthy and slowed down service to customers. In addition, the back and forth shipping added cost to end users.

Our Solution

Setra was able to provide custom housing modifications to allow the customer to calibrate “in house”, where the competitor was resistant to satisfy their needs. This enabled the customer to provide their customers recalibration times in days instead of weeks.

Through the modifications made to the sensor housing, Setra gave the customer the ability to perform their own recalibrations on-site and to store the recalibration data locally in their internal calibration database. These changes increased both the value they can provide to their customer and the revenues they can generate for the company. The customer can now store historical information for their customer base using their internal system. They were also able to reduce lead times for recalibration to a standard of 2-3 days while minimising shipping costs back and forth.

What is Barometric Pressure?

Barometric pressure is the measurement of air pressure in the atmosphere, specifically the measurement of the weight exerted by air molecules at a given point on Earth. Barometric pressure changes constantly and is always different depending on where the reading takes place.

Average barometric pressure at sea-level is commonly cited as 14.7 pounds per square inch (PSI). This is typically an average figure and in reality this can vary across the world, particularly at higher elevations where atmospheric pressure is much lower than at sea level. As a fact, there are 50% fewer air molecules at 18,000 ft. then there are at sea level. One of the ways that aircraft can determine what altitude they are flying at is by measuring outside air pressure. Altimeters can read air pressure relative to a calibrated ground reading and convert that information to a readout in feet or meters.

Barometric pressure also changes with the weather (the weather changes with changes in barometric pressure). Being able to measure, analyse and record small changes in atmospheric pressure helps meteorologists track the weather and predict rain/storms. Weather services operate a large array of data buoys across the Pacific and Atlantic oceans to serve that function. Being able to precisely read and transmit data on pressure changes from these stations is crucial in tracking large storm systems like hurricanes and typhoons.

For a brief overview of pressure readings, please watch the video below: 

Why is High Accuracy Measurement Needed?

While changes in barometric pressure aren’t immediately obvious to human perception (except when your ears pop while hiking up a mountain), its effects can manifest themselves in many other ways. This is especially true in sensitive industrial and laboratory settings.

Many research and development labs will use barometers to measure the barometric pressure at one facility then use that data to replicate the exact same environment at another research lab. For example, when testing at a lab in the UK versus one in US, the barometric pressure can be significantly different. This can have adverse effects on the results of the test or experiment. Unless they’re testing in a completely perfect vacuum, lab technicians need to compensate for this factor.

A more accessible example on the effects of atmospheric pressure is baking. Because the rate in which fluids evaporate changes with high or low pressure, cooking times and durations need to be adjusted at higher elevations.

Stability and accuracy are the most important aspects of a barometric pressure sensors. These devices are often used on remote weather stations and data buoys where routine recalibrations are simply not practical. Setra’s ceramic technology makes our sensors some of the most stable and accurate in the market; thermal hysteresis is very stable especially on ceramic sensors.

Application Examples

Barometric sensors are used in several applications where high accuracy and stability are required, including:

• Research Laboratories - as a standard reference, gauge or relative pressure transducers cannot be used because the reference changes every time you are doing a test (i.e. if atmospheric pressure is different, it will affect the pressure being read).
   
• Differential Pressure - applications at nuclear facilities. Stability and accuracy allow sensors to be used for long periods of time, which is important because once the sensor wears down, it must be disposed of (sensors cannot be recalibrated because they will be contaminated with radiation).
   
• GPS/Location Accuracy - barometric pressure can change the accuracy of mobile signals that bounce off mobile phone towers – measuring and compensating for barometric pressure can help pinpoint location, even within a building.
   
• Aircraft Altimeters - Altimeters, a vital component within an aircraft, calculate and display altitude by measuring the barometric pressure and converting that measurement into altitude. The greater the altitude of the aircraft, the lower the altimeter pressure reading.

Digital Altimeter Setting Indicator (DASI) Systems

The Digital Altimeter Setting Indicator (DASI) System is a critical part of flight control and instrumentation. It assists with calculating the true altitude of an air plane relative to the ground. Pilots use this altitude calculation for landing aircrafts safely on the runway. Without this system, pilots wouldn't have accurate altitude measurements accessible to them prior to landing.

Altimeters produce readings with respect to sea level. This is an inaccurate reading as a result of weather patterns and varying elevations of airport locations. Changes in weather can alter the readings at an airport control tower. As weather patterns move, high and low pressure fronts change the pressure seen at the fixed location. Since each airport has a unique elevation, using the aircraft's altitude in reference to sea level would greatly mislead the pilot.

A new reading should be taken during each flight so that the altitude can be properly corrected. The altimeter's reading is adjusted through a barometric pressure reading taken at airport control tower, which is then relayed to the pilot prior to landing, ensuring proper landing of the aircraft. Without the altitude adjustment, an aircraft could prepare to land on the runway too soon or too late, causing major safety issues.

Summary

We can help assist you with selecting the right barometric pressure sensor for your application. For guidance, please contact our experienced technical team here for application support and advice on components for your system.

If barometric pressure sensors aren't right for you, please visit our detailed guide on types of pressure sensors for an overview of what is available.