25 January 2012

How to take IRR Temperature Measurements without a Datalogger

Customers occasionally ask us if it is possible to use our infrared radiometer (IRR) sensors without a programmable datalogger. This is difficult, but not impossible. This blog describes the requirements.

For starters, a voltmeter with microvolt accuracy is necessary since the target output of the sensor is only 30 to 60 microvolts per degree C. Dataloggers from Campbell Scientific have an accuracy of 0.33 microvolts, which is adequate to determine the temperature of the target to 0.01 C. Be careful not to confuse the resolution of the display with the fundamental accuracy of the voltmeter. Few voltmeters have the accuracy necessary to make a good measurement.

The voltage signal often needs filtering to improve the signal to noise ratio. The most typical filtering is 60 Hz integration, which filters out interference from nearby power sources. This may not be necessary in the middle of a field, but it is typically necessary in a laboratory environment.

After an accurate voltage measurement is made, it is necessary to convert the voltages from both the target sensor and the sensor body temperature into degrees C. This requires multiple steps. These steps are automatically done in a CSI datalogger, or done by downloading the program that comes with each sensor.

The first step is to convert the voltage output of the sensor body to temperature. This is measured with a precision thermistor and a precision bridge resistor. Set the multimeter to resistance mode with the resolution in the kΩ range. Next, place the leads onto the green and white cable ends of the IRR. Record and mark the measurement made as “RT”, in ohms.

The next, more complex step, is to convert the voltage output from the target sensor to degrees C. Make sure the resolution of your device is to the appropriate range, as typically all signal sizes of IRRs vary between -1.0 and 1.5 mV. Place the positive and negative leads from your multimeter onto the red and black wires, respectively, of the IRR cable (see figure above for IRR wiring help). Record and mark the measurement made as “mV” for future reference. Now that we have taken all of the necessary measurements for a surface temperature reading, we need to make a few calculations to convert RT to a sensor body temperature.


Campbell Scientific dataloggers use an intrinsic function called “Therm109” in datalogger programs to convert RT to a temperature in °C. However, this can still be done manually by using the Steinhart-Hart equation below:

  where A = 1.129241E-03, B = 2.341077E-04, and C = 8.775468E-08.

With the sensor body temperature (SBTempC) of the IRR calculated, we can finally proceed to incorporate the custom calibration coefficients for the final target temperature.

With every calibrated IRR sensor we sell, there is a set of custom coefficients which are needed to provide the user with the actual target temperature measurements desired. The custom coefficients are labeled mC2, mC1, mC0, bC2, bC1, and bC0 (as marked by the stars in the figure above). The equations below will show how these work. Two temporary variables, “m” and “b” which correlate with our calibration process, will be calculated as follows:

After calculating m and b, we take our mV measurement, and use our final equation below, to determine the IRR sensor target temperature in °C :

A couple of final comments: when taking measurements, ensure that your sensor remains in a stationary position, pointed at the target. Obstructing the sensor during measurement will cause incorrect readings, as well as holding onto the sensor body without the shield on, due to heat conduction effects. Additionally, taking the mV and RT measurements as concurrent as possible will provide optimal results. Provided below is a link to a starter excel spreadsheet that can be downloaded to help you take manual temperature measurements from your IRR. Simply fill in your custom calibration coefficients in the orange cells near the top and input your mV and RT measurements in the orange columns below, and you will have your desired target temperature in the green column. Happy measuring!




Adam Del Toro
Mechanical Engineering

18 January 2012

Need a Custom Solution?

Recently, we were approached by a prospective customer inquiring about making reflective measurements of a standard Macbeth ColorChecker 24 chart. After working out the details, the customer would supply the chart and Apogee would supply the 24 reflectance files with useable data from 400 to 1000 nm and a spectral resolution of less than 5 nm. This provided an obvious benefit to the user in that they were able to continue their research without having to spend the few thousand dollars to purchase a spectrometer, but also we got to learn about a Macbeth ColorChecker and how it reflects radiation in the visible and near infrared!

At times we also receive requests to customize our existing products to help better suit the requirements of the end user's specific application. While some customizations can only be matched with that unique application, others have led to further development of new product offerings. As an example of this, when the Jet Propulsion Laboratory asked if we could supply our infrared sensors with a narrower field of view than the 18° half-angle of the SI-121, we went to work on it. After some modifications we were able to provide a sensor with a 14° half-angle and now it is offered as the SI-131. Additionally, it's not unusual for a custom sensor to draw immediate interest from other users in a similar niche – usually after much searching for the same modification. And in many cases, it's ultimately these modifications that help improve and advance the function of a sensor.

As a smaller company, we feel that we have retained much of the flexibility required to work with an end user to come up with a solution to their measurement predicament. To offer a service or custom sensor certainly opens the doors to a variety of ideas, but it's precisely those ideas that can provide the path for finding a solution to your own measurement dilemma. Feel free to send us an email if you think we might be able to help with a specialized service, or if you find that any of our sensors are just not quite what you require.



Jacob Bingham
Customer Support and Technical Manager

11 January 2012

Governor's Award

Teryl Roper and Bruce Bugbee
Last night (10 Jan 2012) Dr. Bruce Bugbee was awarded the Governor’s Science and Technology Medal for 2011 at an awards banquet held in the Discovery Gateway Children’s Museum. When the medal was presented to Bruce by Governor Herbert, a few accomplishments from Bruce’s work at Utah State University and at Apogee Instruments were briefly mentioned. Before the banquet several of Bruce’s guests were conversing and the question came up of regarding the nomination process and what Bruce had done to merit such consideration. Bruce replied that he had done “nothing in the past year” that was deserving of the award, but that rather it was something of an acknowledgment of lifetime achievement. My disagreement with this statement is that in the seven years I have personally known Bruce he has not slowed down one bit and has many years of achievement ahead of him.

While the awards ceremony was necessarily brief, I would like to take this opportunity to share a personal view of Bruce Bugbee, garnered from my work experience at Apogee Instruments. Bruce is a brilliant scientist, whose curriculum vitae can be seen at the crop physiology web site, http://www.usu.edu/cpl/general_info_bruce_cv.htm. Please indulge me while I share a personal insight of Bruce Bugbee.

Mary Heers, Bruce Bugbee, Kookie Tanner, Diana West
 Two of Bruce’s guests to the awards ceremony were long time friends Kookie Tanner and Mary Heers. We were discussing Bruce and how much he accomplishes at both USU and Apogee. The comment was made “I don’t know how he does it,” to which I replied that I had some idea. Bruce is the hardest working individual I know. I receive emails from him at 10 p.m. and they start up again at 6 or 7 a.m. He barely stops for sleep and rarely stops to eat. In December of 2011 Bruce and I were in San Francisco for the American Geophysics Union annual meeting. We were going out to dinner at a Thai restaurant with several colleagues from Campbell Scientific, including Larry Jacobsen and Sasha Ivans. While we were waiting for our table to be ready the conversation turned to how inefficient eating is and if there wasn’t a better way to consume calories. Bruce was interested in the question of “How many calories are there in gasoline?” In other words, is there a way I can spend less time eating so I can devote more time to what I love?

Another annual meeting that Bruce attends is for the Agronomy Society of America. Bruce likes to share the story that many years ago the show was held in Las Vegas but afterwards the Society was invited to not return to Las Vegas for their annual meeting. Apparently there was a noticeable dip in the earnings at the poker tables and other offerings when the crop and soil scientists were in town. In reference to that Las Vegas meeting Dr. Gaylon Campbell, founder of Decagon Devices and professor at Washington State University, said they “showed up with a twenty dollar bill and a copy of the ten commandments and didn’t break either one.” Bruce is fiscally responsible and yet at the same time, very generous to his employees at Apogee. When he was designing our current building, he wanted to have a building where employees would be proud to work. Bruce and Apogee have also started a policy of donating a percentage of the annual profit to non-profit organizations in our area to help the community.

Bruce’s generosity is based on his deep, caring concern for other people (and animals). If you call his home phone and get the answering machine, you will be greeted by Bruce, welcoming you to the home of “Bruce, Anna and Coconut.” Anna is Bruce’s daughter, whose school science fair posters have adorned the halls of the research greenhouse at the USU campus. Coconut is their cat, who has his own graph in Bruce’s home, charting his weight over several years. When the father of an employee at Apogee passed away, Bruce wanted to do something other than send the expected flowers. Instead Apogee planted a Magnolia tree with a plaque in honor of her father.

The keynote speaker at the awards ceremony talked about the convergence of science and math while doing a sculpture of Leonardo da Vinci. Leonardo was described as a Renaissance man, someone with broad intellectual interests spanning both science and math. In discussing scientists, he said that the highest praise you can give a scientist is to describe his work as elegant, that it is precise, simple and yet profound. Years ago at an Apogee Christmas Party, our graphic designer described Bruce as a Renaissance man. Bruce is a brilliant scientist and more. It is a privilege to work with Bruce, whose life and work are truly elegant.


Devin Overly
General Manager

Press Releases:

Utah Pulse

Utah State University

Salt Lake Tribune

04 January 2012

Extreme Weather Conditions

I thrive in harsh weather conditions, especially extreme cold. One year at the end of June, I did some work in Houston. It was 38 C (~100 F) and felt like 100 %RH outside but in the confined environment where I was working it was about 49 C (~120 F) and felt like 200 %RH. Another time, while helping a local scout troop, I set up an orienteering course near the head waters of the Missouri river in temperatures well below -18 C (~0 F). I have even commuted to work on my bike in temperatures below -29 C (-20 F). As humans, we can adapt and survive such conditions but can the sensors and instruments on which we depend also survive?

When discussing survivability of equipment in extreme environments many factors must be considered that do not affect operation at room temperature. Perhaps the largest factor is a mismatch in coefficients of thermal expansion between materials. For example, aluminum has a larger coefficient of thermal expansion than stainless steel. Two parts that fit tightly at room temperature may not fit tightly at -30 C. This fact can be used to create tight fits between two rings, an inner one of aluminum and an outer of stainless steel. When submerged in liquid nitrogen, they will fit easily but once brought back to room temperature the fit may not be tight enough to create a water tight seal.

While this method creates a tight seal, often materials will contract differentially creating a gap between them in which water might condense. After several freeze/thaw cycles two pieces formerly bonded can separate.

We continuously test our pyranometer sensors on the roof top of our building and have many years of experience in this environment. We continually monitor their output and compare them to primary standard reference sensors.

Our pyranometers were designed with color in mind. In cold environments, the sun warms the head causing frost and snow to melt off the sensor more quickly. You might expect that this black color would be an issue in blazing Death Valley type heat. However, the heads only get to about 12 C above ambient air, in conditions with almost no wind and at peak solar intensity. We have also tested the temperature dependence of the pyranometer. At extreme hot and cold temperatures, the sensors vary by less than 5%.

Our temperature sensors are also highly water resistant. We used ST-100 temperature sensors in warm (60 C), mild brine solution for 2 months. We then did 30 days of accelerated aging tests (3 hour cycling from -20 to 60 C). These sensors still meet specification.

We tested our SB-100 barometric sensor both indoors and outdoors. We compared it against a more accurate and more expensive Setra pressure sensor, model #276, for 4 months. Inside our building, the largest error measured was < 0.03 kPa. Outside in a weather proof box, near ambient temperatures, the largest error was < 0.2 kPa. This SB-100 provides a very low cost, accurate sensor for weather stations.

Comparison of two Apogee SB-100 pressure sensors (one inside, one
outside) with a Setra Model #276 pressure sensor (inside). The plots are
absolute pressure (kPa), pressure difference (kPa) with reference to the
Setra sensor, and outdoor temperature (Celsius) for more than 140 days
over a wide range of outdoor temperatures.

Our quantum sensors are used in a wide variety of applications. In fact, some of our customers use our quantum sensors to monitor lights in salt water tanks for coral growth. They are repeatedly submerged and often left in the bottom of tanks; they continue to perform.

Our sensors survive, not by chance, but by design. When our building was being constructed one of the beams was a few feet too long. Rather than let that go to waste, we built a sign out of it that now hangs above our employee break area. It is inscribed with a tag line under our logo that says: "built to last". Our sensors weather the worst.


Seth Humphries
Product Development Scientist