28 March 2012

Business Ethics

More than ten years ago I worked as a lab manager for a biotech company. My job responsibilities were diverse and part of it included acting as an intermediary between the CEO and CFO of the company with the employees. As it happens in many companies, a situation arose where an employee was not a good fit for the company. Opportunities to change had been repeatedly extended without result and it became apparent that the company and this employee needed to part ways. I was asked by the CEO to inform the employee that the CEO and CFO wanted to speak with him. Once that message was relayed I was asked point blank “Am I being fired?” Due to my position I was privy to information that I could not share and in fact I had been directed to tell this employee that I did not know the nature of the meeting, only to relay that his presence was needed. The end result of this experience is that the employee, after being let go, continues to bear great animosity towards me for lying to him. And so I pose the question, rhetorically and to myself, “Did I act with integrity?”

I have been with Apogee for seven years and in that time many occasions have arisen to test my integrity. I have always striven to deal with our customers in a manner that is above reproach. Several years back it became apparent that an adhesive we were using failed in certain circumstances, which could lead to disk separation. We had years of data from Logan, UT where the sensors are built and had not found any evidence of this issue. However, as reports began to trickle in, we discovered that in hot and humid environments, our sensors were not performing as designed. As we gathered data and focused our efforts on a solution, the question arose of informing our current customers of the defect. In the end, we resolved to notify all of our customers to the best of our ability of the situation. We explained the environmental conditions where the issue was most likely to arise and developed a tool, the Clear Sky Calculator, to allow researchers and users of all pyranometers a method to check the accuracy of their sensors in the field. I feel comfortable that Apogee acted with integrity throughout the process.

Another example on a smaller scale is being upfront regarding the performance of our products. Our quantum sensor does not have a perfect spectral response. It is our position that if the application conditions match those of the calibration, our sensor will perform as well as those market leaders that cost three and four times as much. However, if you need to use our sensor under different light sources, spectral differences in the light source can lead to errors when using our sensor. We publish these differences on the web and educate our customers on what they can expect. I have communicated with many customers, on the phone, via email and in person and they are frequently surprised when I inform them that for their application, a competitor’s product would better suit their needs. Again, this is what I feel it means to act with integrity.

It is our company motto that we strive to help you “make better measurements.” We feel that by acting with integrity we will develop a relationship of trust with our customers. In being honest about the shortcomings of our products we may lose a sale of a hundred dollars but gain the respect and appreciation of a customer that will return to us for other sensor needs. As customers use our products and get the results they expect, they will share their experience with colleagues. A strong endorsement from a respected scientist benefits us much more that a host of advertisements on the web and in print media. This is why we strive to act with integrity as we help you make better measurements.


Devin Overly
Business Manager

21 March 2012

A Brief Review of Temperature Measurements

The properties of materials and nearly all biological, chemical, and physical processes are temperature dependent. As a result, temperature is perhaps the most widely measured environmental variable, and there are multiple sensors, or thermometers, available to measure temperature. Some of the common thermometers for automated temperature measurement are:

Thermocouple: two different metals or alloys connected at the ends (see Figure 1 below) to form a simple electrical circuit (current loop). A temperature difference (thermal energy gradient) between the two ends of the circuit produces a voltage, called an electromotive force (emf), that is proportional to the temperature difference.

Thermistor: electrical resistor, often ceramic (see Figure 1 below), where resistance changes with temperature.

Platinum Resistance Thermometer (PRT): platinum coil, where resistance changes with temperature. Thermistors and PRTs are similar and operate via the same mechanism, but are made with different materials.

For temperature measurement with the thermometers listed, changes in the physical property (voltage, electrical resistance) related to temperature changes must be measureable, repeatable, and stable. These thermometers require a meter to make the electrical measurement and convert it to temperature. This is desirable for environmental monitoring, where many meters can log data, and automated data collection of high frequency and/or long-term data sets are often required. A summary table (Table 1) is provided to highlight the advantages and disadvantages of thermocouples and thermistors. The advantages and disadvantages of PRTs are similar to or the same as those for thermistors, except that the sensitivity (resistance change) in PRTs is much smaller and potentially more difficult to measure accurately.

Figure 1. Size comparison of thermocouples and thermistors. From left to right: human hair (for scale), fine wire ceramic thermistor with thin epoxy coating, ceramic thermistor with epoxy bead coating, 30‐ AWG (0.2546 mm) type‐E thermocouple, and 24‐AWG (0.5106 mm) type‐E thermocouple. Thermocouple junctions are often coated with epoxy for electrical isolation and waterproofing, however, those in this picture are bare wires.

Table 1. Advantages and Disadvantages of Thermistors and Thermocouples

 Some of the advantages and disadvantages listed in Table 1 are dependent on the circumstances of the specific measurement and application. Multiple datalogger program steps for many thermistors are avoided with dataloggers that have ‘canned’ thermistor instructions. A ‘canned’ instruction is a set of pre‐programmed datalogger codes that allow use of specific sensors with only a single instruction. Also, the power requirement of thermistors is extremely small. For example, a commonly used thermistor in environmental applications only uses 0.056 mW at 20 C. The maximum current draw across a wide range of temperatures is approximately 0.090 mA. A commonly used datalogger can source 25 mA. Based on this specification, the datalogger could accommodate over 250 thermistors if there were enough measurement channels available.

The reference temperature required for thermocouples is available on many dataloggers. Accurate reference temperature measurements are then dependent on the accuracy of the sensor used to measure it. This is often a thermistor. Periodic recalibration of the datalogger is recommended to ensure the thermistor is accurate. Also, the datalogger wiring panel (where the thermocouples are connected) should be kept isothermal. This is best accomplished by installing the logger in an insulated, weatherproof box that shields the logger from solar radiation. The small output signal of a thermocouple relative to the large output signal of a thermistor is only a disadvantage when a low resolution datalogger is used to make measurements. Some dataloggers have adequate resolution to make highly accurate thermocouple measurements. The datalogger program required for thermocouples is only simple because it is generally always available as a ‘canned’ instruction. If thermistor and thermocouple datalogger programs had to be written from scratch, the number of program steps and the difficulty level would be similar. Because thermocouples require a differential channel and thermistors do not, this is always a disadvantage. This means twice as many thermistors can be connected to the same number of datalogger channels



Mark Blonquist
Chief Science Officer

14 March 2012

New Product: 4-20 mA Output Pyranometer (SP-214)

Solar radiation is usually measured in agricultural, ecological and hydrological studies. The need for power conservation has increased the use of pyranometers in industrial and energy applications, such as solar power and building monitoring. These industries often use data collection systems that are not designed for a millivolt input signal. Apogee amplified sensors have often been used for these applications, but were limited by input voltage and output voltage requirements. As such, we have had an increasing number of customers asking if we sell radiation sensors with a 4-20 mA output to match their data collection system. This blog will outline some of the reasons to use a current output sensor, as well as some of the specifications of the Apogee 4-20 mA pyranometer (SP-214).

Advantages of current output over voltage output:
  • Long Cable Runs – there is no current drop due to cable resistance. 
  • Noise Immunity – the data collection system usually has a low input impedance and also because most noise created is a voltage and not added current. 
  • Programmable Logic Controllers – these commonly have a current input and not a voltage input. 

Some of the specifications of the SP-214 include: 
  • 5-36 V input voltage 
  • Multiplier of 78 W m-2 / mA 
  • Offset of 4.0 mA 
    • The Offset of 4.0 mA is a good way to check if the sensor is working correctly. An output of 0 mA indicates that the circuit is not functioning properly which could be due to a loss of power, a break in the wire or any other problem that might arise. 
  • 2 mA quiescent current draw o 22 mA max current draw 

**IMPORTANT** Due to limitations of the circuitry the output voltage must be, at most, 2 V less than the input voltage. The output voltage is calculated by adding the wire resistance to the input resistance of the data collection system, and then multiplying by 0.02 (20 mA). This means that if a 5 V power supply is used the total resistance must be less than 150 Ω.

5 V – 2 V = 3 V = 150 Ω * 0.02 A

The SP-214 also has the same specifications as other Apogee pyranometers.
  • ±5 % Absolute Accuracy 
  • Excellent Cosine Response 
    • ±1 % at a 45° Zenith angle 
    • ±5 % at a 75° Zenith angle 
  • Designed for Long-Term Outdoor Use 
    • -25 to 55 C Temperature Range 
    • 0 to 100 % Humidity 
    • Head can be submerged in water 

Silicon cell pyranometers can also be more effective as measuring solar panel efficiency as explained in this blog by Seth Humphries: “Why silicon pyranometers are the best choice for monitoring solar photovoltaic panel efficiency”

This is just one new way we are helping you make better measurements.

For more information see the spec sheet and owner’s manual.


Skif Smith
Electrical Engineer

07 March 2012

Protecting Your IRR from Spiders

When making measurements and carrying out experiments, scientists tend to spend a great deal of time and care in selecting the right instruments, calculating uncertainty, and making sure conditions are acceptable. One of the last things on the minds of most people (and rightfully so) is that a pest, like a spider, could find a way to sabotage an experiment or measurement campaign. As spring approaches, many pests (including our 8-legged friends) will awaken in full force, ready to cause havoc. Don’t worry; they aren’t really out to get you! Spiders and other insects sometimes just see the aperture of an infrared radiometer (IRR) as their new comfortable home. There are some simple steps to prevent IRRs from looking like the photo below.

Spider webs can cause inaccurate readouts.

Important Steps to preventing sabotage by pests 

1. Check on your sensor often.
2. Sensor Placement.
3. Repellant.

How “often” depends on a couple of factors such as: what the sensor is measuring, whether it is outdoors or indoors, where the sensor is located, etc. For example, if you had an IRR sensor making measurements outdoors and in close proximity to thick shrubbery (spider magnet), you might want to reconsider the location of the IRR. If the location cannot be changed, I would recommend checking on it at least weekly. If your sensor is located high on a weather station, which you only visit once a month, it can be helpful to monitor and compare measurements from day to day if the data acquisition system allows. If you suspect something is wrong with readings, check the IRR next time you go out for a visit. Better safe than sorry.

Choosing and applying a repellant can be a little tricky. Some commercial repellants can be harmful to humans, due to their potency. They can also be corrosive, which can be detrimental to the longevity of an IRR. Another option is to use essential oils such as lavender, lime, lemon, orange, tea tree, etc., which naturally deter spiders and other pests while being non-toxic to humans. Whichever repellant you select, take all the safety precautions recommended on the container. To apply the repellent, use a cotton swab and carefully rub the repellant on the wall threads of the IRR aperture without touching the sensor window, as this can cause a change in readings. You may need to reapply the repellant occasionally.

If you are already having problems with other pests, like wasps, or anticipate it this spring, I recommend reading Seth Humphries’ blog from last month titled: “Minimizing problems with wasps on weather stations. 

In the event you have an unwelcome visitor in an IRR, carefully brush it away with a cloth and carefully clean out any remaining spider webs with a wet cotton swab. While I don’t recommend keeping spiders as pets (unless you’re in Cambodia where cooked tarantula is a delicacy), I do recommend keeping them off your sensors, especially out of the aperture of an IRR.

Adam Del Toro

Mechanical Engineering Intern