Setra Barometric Pressure Transducer Is An Accurate Forecaster
Weather-station monitoring systems not only help to determine whether we need to bring an umbrella to work, they are also counted on for accurate forecasts to maintain flight schedules and to keep passengers safe. Natural disasters such as hurricanes, tornadoes, and floods claim far fewer lives than they once did, thanks in large part to advances in the science, technology, accuracy and immediacy of weather forecasting.
Because accuracy in forecasts is paramount to safety, it is essential that the companies manufacturing weather-station monitoring systems use the most technologically advanced pressure transducers available on the market today. That's why Wescor International of Logan, Utah is using the Model 278 barometric pressure transducer from Setra Systems Inc. of Boxborough, MA as the transducer-of-choice for their S-470 barometer.
Wescor's Environmental division is an important supplier to the federal government, universities, municipalities, various industries, and to a lesser extent, the U.S. Military.
The company's comprehensive range of weather sensors includes everything from anemometers (measuring wind speed and direction) to solar radiation sensors to soil moisture sensors to leaf wetness sensors. One of Wescor's most important environmental monitoring devices is the S-470 Barometer, a key component in the company's complete Weather-Station Monitoring systems and an ideal partner for the company's DataLoggers. By using the Model 278 from Setra, which is marketed as Wescor's S-470 barometer, Wescor is assured that their barometric readings are stable and accurate.
Setra Systems, a designer, developer and manufacturer of a wide range of high accuracy instrumentation for measuring pressure and vacuum, met all the criteria Wescor was looking for in a barometer, and then some.
According to Kathy Abel, Sales Manager for Wescor's Environmental Products Division, "Setra's Model 278 has the fast, dynamic response and accurate, high level output signal that customers of today's technologically advanced weather-station monitoring systems require. Plus the company itself had the responsiveness Wescor demands, with the ability to deliver a great product at a great price in just two to four weeks."
Advantage: Setra.
It was the job of Lynn Leishman, Wescor Senior Technician, to put the Setra 278 to the test. In his role as senior technician, it was Leishman's responsibility to determine if the 278 could match or even surpass competitive brands in terms of performance.
"For about a year, I've been testing the Setra 278, side-by-side against available transducers, including the competitor's model we had been using" Leishman said, "the 278 provided virtually the same accuracy and performance, while surpassing the competitors' models in a number of areas."
The accuracy of the Model 278 is specified over the full temperature range of -40º to +60ºC (-40º to +140ºF), rather than as a percent of full scale, with accuracies to within ±0.3 hPa/Mb of the Full Scale pressure range. This method provides a more precise reading for monitoring atmospheric trends. In addition, Setra's 278 is available in pressure ranges from 500 -1100mb, 600 to 1100mb, and 800 to 1100mb, which covers the entire working range of any of the Weather Station Monitoring systems that Wescor offers.
One important area in which the Setra 278 maintained a firm advantage over competitive transducers was with its linear analog output. This makes the 278 more compatible with Wescor's Datapod DPXe series and Easy Logger 900 series DataLoggers. This linear analog output assures the customer that the accuracy of the output signal produced by the 278 is proportional to the applied pressure.
"All of the data loggers we build at Wescor are voltage loggers," Leishman said. "Some of the sensors we've previously used required that we add a resistor to the circuitry to convert this information into voltage. The 278 is more of a plug-and-play solution, as it doesn't need the addition of extra equipment like a resistor. It produces an output signal that's linear with the pressure range, output that's a lot easier to read and work with."
Quickly and accurately responding to pressure - and drops!
The 278 is housed in a rugged metal fiber filled polyester case, which aids in its stability and makes it resistant to EMI/RFI interference, ensuring a very stable, accurate output.
Leishman also determined, in part by accident, that the Setra 278 was able to demonstrate exceptional output stability, even in harsh environments.
He explained, "We put the 278 in a controlled environment and saw approximately a three microvolt variation in the output voltage. That's more than satisfactory. We also tested the 278 for interference from outside electrical and magnetic environments and the 278 performed almost flawlessly compared to the competition. This is very important because the customer doesn't want to get a false reading and thus a false barometric pressure reading. A stable reading is critical to the overall operation.
"Plus we learned that the Setra system's rugged housing adds to the system's stability. Every once in a while, I do get clumsy. The transducer I have in my hand here I've actually dropped a couple of times onto a concrete floor from about 6 to 8 feet. Even so, I've seen no change in its operation."
"Its very stable ceramic sensor doesn't expand or contract like stainless steel," Leishman elaborated. "This helps ensure the sensor's long-term stability with minimal drift over time, even when dealing with extreme temperatures. As Wescor weather stations have homes in places where temperature ranges are extreme, such as atop mountains, it's essential to keep any flexing, contracting or expanding to a minimum."
A dual benefit.
Leishman also credits the Setra 278's dual electrode design with contributing to the sensor's long-term stability in the field. Using this dual electrode, the 278's capacitance sensing technology cancels out all outside environmental factors, such as temperature fluctuation and stray capacitance.
The Model 278 also utilizes Setra's Setraceram(TM) capacitive sensor and proprietary custom IC analog circuit. Its thermally stable glass fused ceramic sensing capsule is coupled with Setra's sophisticated capacitance charge-balance IC circuit where accurate signal conditioning and environmental compensation is performed. The Setraceram(TM) sensor provides excellent thermal expansion coefficient and low mechanical hysteresis, which contributes to the long-term stability of the Model 278.
Not a big consumer.
Because it is essential for weather forecasters to have the most responsive equipment, the Setra Model 278 barometric pressure transducer has an instant wake-up feature (1 second from sleep mode), making it ideal for environmental applications requiring quick pressure readings. In fact, the energy-efficient Model 278 consumes less than 3 mA of power during operation and less than 1uA during sleep mode. Also, the 278 operates on DC power, important in that many of Wescor's customer installations do not have available AC power.
Leishman added, "It's important for our barometer to consume low levels of power because our Weather Station Monitoring systems are often housed in remote locations and rely on battery power. We can't have our weather station go down because the battery has gone dead. The Setra 278 meets our needs by consuming very low levels of power, and by working in solar or battery-powered weather stations."
The low power consumption of the 278 is in part due to its sleep mode functionality, but when needed to perform, the product has the instant wake up feature that allows for instant pressure readings. As Chris Duchesneau, Application Engineer for Setra Systems said, "Unlike competitive units, Setra utilizes an external jumper to enable and disable the sleep mode. The jumper not only ensures a quick turn on feature, but because it is external, the internal electronics of the unit are protected from accidental damage."
Duchesneau further explained, "On a competitive unit with an internal jumper on the circuit board, the back plate has to be removed to enable or disable the sleep mode."
According to Duchesneau, "Changing an internal jumper is awkward one slip of the screw driver and you risk knocking a component off or damaging the sensor, which is a costly repair."
To further protect the 278 from failure, the 278 is reverse wire protected. This means that if the 278 is wired incorrectly the electronics will not be damaged.
Setra's Duchesneau points out a key advantage of this reverse wiring feature: "Some of the units we sell are going to a university lab setting where they're being worked on by students who are relative novices when it comes to wiring. The reverse wiring definitely shortens the learning curve."
Sensing complete satisfaction.
Wescor's DataLoggers not only take the transducer's raw data and convert it into units that their customers can read, they also serve as a power source to the Model 278. The Setra transducer's output, either 2.5 VDC or 5 VDC, with 9.5 to 28 VDC excitation, makes it a perfect partner for Wescor's DataLoggers, and its external five pin terminal strip allows the connection to be made with ease.
Compact in size (3.6" x 2.4" x 1.0"), Setra's transducer is extremely easy to install and convenient to use. "It's a perfect fit for our customers' weather stations," Leishman concludes. "And it perfectly suits our needs as well.
"Plus we've received absolutely fantastic customer support from Setra. With our previous transducer supplier, we'd be lucky to even be able to talk to somebody on the telephone. Setra engineers have been very available to us, even physically coming to our site in order to answer any and all questions we may have. We would certainly considering using Setra and their other sensors in the future to handle other environmental monitoring applications."
It appears that we can safely forecast a long and successful relationship for Wescor and Setra. And meteorologists will continue to have the technologically advanced equipment they can count on to deliver accurate forecasts that keep us all dry, comfortable and safe.
CONTACT:
Charlene Cloney
Gray & Rice Public Relations
617-367-0100 ext. 107
ccloney@gr2000.com
