Kestrel Wind & Weather Support

Kestrel® 3500 Delta T Pocket Weather® Meter Instructions (Printable PDF)

Thank you for purchasing the Kestrel 3500 Delta T Pocket Weather Meter. This instrument will measure the following environmental conditions:

• wind speed
• heat stress index
  
• maximum wind gust
• dewpoint
  
• average wind speed
• wet bulb temperature
  
• temperature (air, water, snow)
• barometric pressure
  
• wind chill
• altitude
  
• relative humidity
• delta T

Plus additional features:

• clock
• 3-hour pressure trend
  
• data hold function
• backlight
  
• automatic power-down function
• waterproof and floats

OPERATION

1. Slide off cover.
   
2. Turn on. Press the center button () to turn on the unit.
3. Select operating mode. Press the right arrow () to scroll through the measurements listed below. Press the left arrow () to scroll through the measurements in reverse order. The instantaneous measurements will be displayed. (See Understanding the Measurements section for more information.)
4. Select the units of measure. Press while holding to scroll through the units of measure.
   

   Mode Hint Icon Units of Measure Clock --- --- 12-hr, 24-hr Wind Speed SPd m/s, ft/min, km/h, mph, kt, B Max Gust SPd MAX m/s, ft/min, km/h, mph, kt, B Avg Speed SPd AVG m/s, ft/min, km/h, mph, kt, B Temperature dEG C, F Wind Chill chill C, F Humidity r.h. % Heat Stress Index H.I. C, F Delta T dELt C, F Dewpoint d.P. C, F Wet Bulb Temp bulb C, F Barometric Pressure*   hPa, inHg Altitude Alt m, ft * Only one of the pressure icons will be displayed, indicating the 3-hour pressure trend. pressure rising quickly (rise more than +0.18 inHg) pressure rising (rise within +0.06 inHg and +0.18 inHg) pressure stable (remain within -0.06 and +0.06 inHg) pressure falling (drop within -0.06 inHg and -0.18 inHg) pressure falling quickly (drop more than -0.18 inHg)

5. Hold mode. While holding , press to hold the time and all of the measured values. The word “HOLD” will blink to indicate the Hold Mode. Press or to view the other measurements in Hold Mode. While holding , press to exit the Hold Mode. This mode can be useful for taking measurements when unable to view the display.
   
6. Turn on the backlight. Press to activate the backlight for 10 seconds. If or are pressed while the backlight is illuminated, the backlight will remain illuminated for another 10 seconds. Press while the backlight is illuminated to manually turn off the backlight.
7. Adjust the clock. Simultaneously press and to adjust the clock. While the clock is blinking, press or to adjust the clock. Hold or to adjust the times quickly. Simultaneously press and to exit the clock adjustment.
   
8. Adjust the reference altitude. Obtain your altitude from a topographic map or landmark to use as your reference altitude. From the barometric pressure screen, simultaneously press and buttons to adjust the reference altitude. Press or to adjust the reference altitude, or hold or to adjust the value quickly. Simultaneously press and to exit the reference altitude adjustment.
   
9. Adjust the reference pressure. Obtain your barometric pressure reading from a local weather source to use as your reference pressure. From the altitude screen, simultaneously press and buttons to adjust the reference pressure. Press or to adjust the reference pressure, or hold or to adjust the value quickly. Simultaneously press and to exit the reference pressure adjustment.
   
10. Turn off. Hold for 2 seconds to manually turn off the unit. The unit will automatically turn off if no buttons have been pressed for 45 minutes.
    
    

UNDERSTANDING THE MEASUREMENTS

• Wind Speed - average over the previous three seconds. The measurement will be accurate for air flow through the front or rear of the unit.
• Maximum Wind Gust - maximum 3 - second wind speed since the unit was turned on.
• Average Wind Speed - average wind speed since the unit was turned on.
• Temperature - instantaneous temperature of the thermistor, which is located at the end of the long coiled leads in the open cavity below the impeller. The exposed thermistor will respond quickly to changes in temperature when air flows past it. For fastest response, either hold the unit into the wind or wave the unit side to side for 15 seconds. Readings should be taken in the shade. Water and snow temperatures can be taken by hold the unit in the water or snow.
• Wind Chill - combination of wind speed and temperature, as defined by the US National Weather Service. Wind chill is the effective temperature on a human or animal at low temperatures due to wind speed. Wind chill readings will be the same as the temperature readings above 45ºF or below 3 mph.
• Relative Humidity - amount of moisture in the air compared to the amount of moisture the air can hold for the given temperature, represented as a percent. Because relative humidity is also a function of the temperature, the response time will be dependent on the temperature response time (see temperature section above). Readings should be taken in the shade.
  
• Heat Stress – combination of temperature and humidity, as defined by the US National Weather Service. Heat stress is the effective temperature on a human or animal at high temperatures due to humidity. Heat stress readings will be the same as the temperature readings below 70ºF.
• Dewpoint – calculated based on temperature and humidity measurements, as a measure of moisture content in the air. If the dewpoint is very close to the temperature, the air is humid. If the temperature and dewpoint are the same, dew will form. If this happens below freezing, frost will form.
• Wet Bulb Temperature - calculated based on temperature and humidity measurements, as a measure of evaporation rate. If the wet bulb temperature is very close to the air temperature, the air is humid. Wet bulb temperature is typically measured by swinging a mercury thermometer with a wet sock on its end for several minutes.
• Delta T - calculation of the dry bulb temperature minus the wet bulb temperature as a measure of evaporation rate. Primarily used in spraying applications, this measure provides an indication of droplet survival. For example, it is not recommended to apply pesticides when Delta T is above 10. A range of 2 to 8 (degrees C) is ideal.
• Altitude and Barometric Pressure - the Kestrel 3500 will measure station pressure in order to calculate barometric pressure and altitude. Changes in either air pressure or altitude will affect these readings, so it’s important to make adjustments as necessary.
  
  First, you will need to obtain either (a) the current barometric pressure or (b) the altitude of your location. You can obtain your current barometric pressure by contacting a local airport or weather service. Set this value as your reference pressure on the ALTITUDE screen to determine your altitude. Otherwise, you can obtain your altitude from a topographic map or local landmark. Set this value as your reference altitude on the BAROMETRIC PRESSURE screen to determine your barometric pressure.
  
  There are two examples for when and how to use the BAROMETRIC PRESSURE and ALTITUDE screens.
  
  First, assume that you know the altitude from one of the sources above. Set the reference altitude on the BAROMETRIC PRESSURE screen to this elevation. As long as you remain at home, you can accurately track changes in the barometric pressure. However, the measurement on the ALTITUDE screen also changes. This value will fluctuate as pressure fronts pass through your location. Since you know your house in not changing elevation, you can ignore this screen.
  
  Now let’s assume that you are planning a day hike and you’d like to track your altitude. Before starting, you’ll need to adjust the reference pressure on the ALTITUDE screen. You can do this by simply adjusting the reference pressure until you reach the elevation of your house. The reference pressure will be the same as the pressure reading on the BAROMETRIC PRESSURE screen. You can now track the altitude as you hike. You can ignore the values on the BAROMETRIC PRESSURE screen, since the pressure changes are predominantly due to changes in elevation.
  
  As with all pressure altimeters, it must be assumed that any change in pressure due to weather is small over the course of one day. If you were to encounter an elevation landmark, you can adjust the reference pressure until the altitude matches the landmark elevation. This will correct the altitude for any pressure changes due to weather.
  

MAINTENANCE & TROUBLESHOOTING

Environmental

Every Kestrel Meter is fully waterproof and floats, and has passed mil-spec drop testing.

Storing Your Kestrel

Avoid storing your Kestrel where it will be exposed to temperatures below -30°C [-22°F] or above 60° C [176° F] for extended periods of time. Doing so may cause permanent damage. (Note that the inside of a car parked in the hot sun can reach very high temperatures.)

Use of the Lanyard and Cover

The cover can be captured on the lanyard to avoid loss. First, remove the cord poplock. Then feed the lanyard end through the large opening in the over and out the slot. Replace the poplock on the lanyard.

Replacing the Battery

When your display becomes dim or disappears, replace the battery. Use a large coin to open the battery compartment. Use only new CR2032 coin cell batteries (available where watch batteries are sold). Wipe the battery clean of any fingerprints and insert the positive (+) pole up, angling the battery downward and pressing it firmly into place. When replacing the battery door, be sure to keep the black rubber o-ring seated in the groove on the case back.

Why does the Impeller Appear Imbalanced?

It is NORMAL for the impeller to oscillate as it comes to a stop. It is NOT imbalanced. Rather, it contains a very small magnet that responds to the earth’s magnetic fields. This does not affect the accuracy of the wind speed readings because the magnetic field applies both a braking and an accelerating force which cancel each other. The impeller has been calibrated to provide wind speed readings accurate to within at least ± 3%.

High Speed Use

After several hours of sustained operation over 25 M/S (~49 KT, 90 KM/H, 56 MPH or 4,923 FPM), the Kestrel will lose some accuracy due to wear of the sapphire bearings in the impeller.

Replacing the Impeller

You may recalibrate the wind speed readings by replacing the impeller. Press FIRMLY on the sides of the black impeller housing with your thumbs to remove the entire assembly. When inserting the new impeller, be sure the arrow is facing the display side of the unit, and is aligned with the top of the meter. Press on the sides of the housing rather than the center.

Taking Accurate Humidity, Heat Stress and Dewpoint Measurements

The patented system for measuring relative humidity allows for extremely fast and accurate readings. The sensor is located in the large hole on the rear of the unit. Even extreme and
abrupt changes in the surrounding humidity will be measured within several minutes. To test this, place your hand around the rear of the unit. Within several seconds, the humidity will increase dramatically. After removing your hand, the humidity will quickly begin to decrease.

Next, place your hand near the rear of the unit and wave the unit back and forth. The humidity will not change because the air flow is diluting the humidity from your hand.

This example shows the importance of keeping air flow past the sensor while taking a measurement. If there is no natural air flow past the sensor, wave the unit back and forth. It is also reasonable to lay the unit down on a solid surface for several minutes to allow the sensor to adjust.

Sensor Calibration

All the sensors have been factory calibrated to be accurate within specifications. For recalibration, you may either return it to Nielsen-Kellerman for factory calibration, or contact NK for field calibration instructions. Humidity Field Calibration Kits are available for sale online.

About the Backlight

The Kestrel 3500 has an aviation green electroluminescent backlight. The Kestrel 3500 NV is olive drab with a visible red backlight - which helps users to sustain natural night vision. The NV’s red backlight preserves the natural night vision of users such as military personnel and pilots. It takes 30 to 45 minutes for the average eye to adapt to darkness and maximize night vision. Even a short burst of white, yellow, green or blue light “bleaches out” the rod cell photoreceptors in the eye and causes night blindness until the entire adaptation process can take place again. Light in the red spectrum does not cause this “bleaching out”, preventing night blindness and night vision fatigue. This unit’s red backlight is also much dimmer than a standard backlight, making it more difficult to detect with the naked eye in night operations.

BEAUFORT SCALE

The Beaufort Scale is a system for estimating wind force without the use of instruments based on the visible effects of the wind on the physical environment. The behavior of smoke, waves, trees, etc., is rated on a 13 point scale. The scale was devised in 1805 by the British naval Commander Sir Francis Beaufort (1774-1857) and is still commonly used by mariners.