Reviews > Environmental Monitoring Gear > Weather Recorder > Kestrel 3500 > Ralph Ditton > Test Report by Ralph Ditton

INITIAL REPORT
KESTREL 3500 POCKET WIND METER
REVIEW BY: RALPH DITTON
DATE: 28th OCTOBER, 2006

                                   Kestrel 3500
                                   (Courtesy of Nielsen-Kellerman)

• Wind speed.
• Maximum wind gust.
• Average wind speed.
• Temperature. (Air, water and snow).
• Wind chill.
• Relative humidity.
• Heat stress index.
• Dew point.
• Wet bulb temperature.
• Barometric pressure.
• Altitude.

• Clock. 12-hr or 24-hr choice.
• Data hold function.
• Automatic power-down function.
• 3 hour pressure trend.
• Back light.

The number of buttons that are required to operate the unit is only three. There is a power on/off central button and two with a left and right arrowhead symbol for scrolling purposes.
To alter settings I had to use a combination of buttons. I wanted to change the time to reflect my local time and by referring to the set of instructions provided with the unit I was able to reset the time to a 12 hr clock.
As the unit of measurements in Australia is metric, I also had to select the following units: Celsius, kilometers per hour and hectopascal.

display/buttons

The display window is 33 mm x 15 mm (1.3 in x0.6 in).
Depending on what is being displayed, the window will show a set of numerals and an icon, apart from the time display.
I find the numerals very easy to read as they are 8 mm (0.31 in) high. However, I do need my glasses on to read the units of measure as they are tiny, only 1 mm (0.04 in) high.

Above the display window, to the left is the thermistor which is located at the end of a long coiled lead. It sits in an open cavity so that, according to the manufacturer, the exposed thermistor will respond quickly to changes in temperature when air flows past it.

Sitting at the top of the unit surrounded by the unit's casing is the impeller. It looks just like the blades of a domestic fan, only much smaller.
The impeller unit can be replaced simply by pressing firmly on the sides of the black impeller housing. The reason why an impeller needs to be replaced according to the manufacturer is that if the unit is used at high speed in excess of 90 km/h (56 mph) over several hours of sustained operation the unit will lose some accuracy due to the wear of the sapphire bearings in the impeller.
 
impeller/coiled lead 

rear view of impeller and thermistor on end of coil

The protective case has an opening at the top and the unit just slides into the cavity. At the base of the cover is a slot for the lanyard to pass through that is attached to the unit.
I have to push down on the unit to when it is nearly housed to fully secure it in the case. It makes a clicking sound when it locks into position.
I do find it difficult to pull the unit out of the case as it is a very tight fit. The easiest way for me is to put my finger into the slot at the bottom and push up to unlock the grip to get it moving, then it is just a matter of lifting the unit out of the case.
          
unit partially in case

side on view
                                                                                    
At the base on the rear of the unit is the battery door. I need a small coin to use as a tool to put into the groove and turn anti clockwise to open. The battery door opens very easily and it has a spring attached to it to act as a tensioner and as part of the circuitry. There are three lugs on the battery door that fit into three recessed slots and when twisted shut, the lugs lock underneath the frame of the battery compartment. There is an O ring that provides a seal against moisture.

battery door
Accompanying the unit is a set of instructions setting out the operation, understanding the measurements, maintenance, Beaufort scale, warranty and service and specifications.
The warranty last for two years from date of purchase and as with all warranties there is a list of disclaimers on what the manufacturer will not cover.

By and large, I found the instructions easy to understand although it took me a few minutes to realise that there were instructions on how to select my units of measure. I was looking for a title along the lines of "How to change the settings" or "How to change from Imperial to Metric". At item 4 the heading is simply "Select the unit of measure" and it wasn't until I held the centre button down and scrolled down with the right arrow button that I noticed the very small units of measure changing from e.g. m/s, ft/min,km/h,mph,kt,B.
I thought I was only changing to the various modes such as wind speed, temperature, humidity etc.
Perhaps the manufacturer should clarify how to set the measurements to another country's standard of measurements.

I had to reset the Altitude in the Barometric Pressure screen as the reference altitude because the unit was initially set at -27 m (88.5 ft) below sea level and I knew that I did not live below the sea level. To obtain my altitude I used my GPS which indicated that I was 3 m (9.8 ft) above sea level and this would appear correct as I live near the river and it is very flat towards the river. In the overall scheme of things, it did not alter the reading of the barometric pressure due to the small adjustment. However, I now have the correct altitude setting for future bushwalking trips.

Expectations from the Web site/Initial impressions
The web site gave a very good front on photo that could be enlarged to show the buttons, impeller, coil details and type of screen display of the Kestrel 3500. What I saw externally I received so there was no difference between the advertised item and the item in the hand as far as appearances go. There were no surprises.
The listed Measures actually tie into the units capabilities.
My initial impression was one of awe as to how sensitive the impeller was. As I walked slowly to go outside from the house, the action of pushing through the air s

• Relatively lightweight.
• Feels good in the hand especially the recess in the rear for my finger.
• Easy to switch between functions.
• Big numerals.
• Symbols easy to understand.

• Extremely tiny letters for units of measure.
• Unit is difficult to remove from the cover. (very minor)

This was a perfect test for the unit as there was a late forecast by the Weather Bureau from a fine day to possible thunderstorms occurring in the late afternoon. The temperature ranged from a high of 24.8 C (76.6 F) to a low of 19.7 C (67.4 F) during my stay at the campsite.

During the drive to my drop off point I had the unit switched on and was mainly interested in the Barometric Pressure to see what was happening. I reached the camp around 3.30 pm after an hours walk.

barometric pressure

Time                 Barometric Pressure             Trend
                          HectoPascal (hPa)
12.30 pm          1012.9 hPa                                    falling
1.47 pm            1013.2 hPa                                    falling quickly
2 pm                 1012     hPa                                    falling
2.11 pm            1010.3 hPa                                    falling quickly (rain drops appeared)
2.17 pm            1008.7 hPa                                    falling quickly
2.25 pm            1006.8 hPa                                    falling quickly
2.28 pm            1005.8 hPa                                    falling quickly
4 pm                 1004     hPa                                    falling quickly
4.38 pm            1003.3 hPa                                    falling quickly
5.08 pm            1004.9 hPa                                    falling (raining heavily)
5.45 pm            1007     hPa                                   stable (still raining)
7 pm                  1013.7 hPa                                   rising (light rain)
8.10 pm             1014.1 hPa                                   rising (light rain)

temperature

This is when I went to bed in my tent.
In the morning when I got up around 6.30 am and left the campsite around 8 am the Barometric Pressure was very stable fluctuating from 1016.5 hPa to 1016.7 hPa.

At 4.38 pm I also recorded the following readings:
Wind Speed : 10.9 kph (6.7 mph)
Max. Gust: 11.1 kph (6.9 mph)
Average Speed: 1.6 kph (1 mph)
Temperature: 23.9 C (75 F)
Wind Chill: 24 C (75.2 F)
Relative Humidity: 43 %
Heat Stress Index: 23.4 C (74.1 F)
Dew point: 10.6 C (51 F)
Wet Bulb Temperature: 15.8 C (60.4 F)

relative humidity

To try and obtain a wind speed reading when I was preparing dinner I had to rest the unit against my camera case so that the impeller was facing into the wind because laying down on the table it didn't give an accurate wind speed as the wind was passing over the top of the impeller instead of through the impeller. Also, I was flicking through the functions from time to time whilst cooking. The temperature sensor also needs air to pass around it through the large hole and laying on a table is not really giving an accurate reading.

As a suggestion, it would be beneficial for the case to have incorporated into it some fold out legs that are recessed. The unit could partially sit inside the case in an upright position with the legs support the case and unit. This way readings could be accurately obtained when the operator is doing other things at the same time. Alternatively, have a slot in the broad side of the case. The unit could  then be inserted in the slot.

The altitude kept changing from 93 m (305 ft) down to 66 m (217 ft). It would go up and down at various times when I was taking readings. According to my map with a scale of 1 : 50 000, tie. 20 mm = 1 km (0.78 in = 0.62 mi), the camp sits at an elevation between 60m - 80 m (197 ft - 262 ft) and the contours are at 20 m (65 ft) intervals. According to my GPS, the site is between 77m and 83 m (253 ft and 272 ft). It is not the most accurate instrument either. The fluctuations of the altitude did not have any apparent affect on the barometric pressure readings when compared to the Bureau of Meteorology records. What I did was to compare my recordings with the Weather Bureau's web page upon my return home and found that the barometric readings were within 2 points of each other. Perhaps Kestrel has succeeded in differentiating between weather changes in air pressure and changes in altitude.

I revisited the Prickly Bark campsite later in the month (Spring) and I recorded the following:
Time: 4. 09 pm                                                     4.55 pm                                         6.21 pm                       6.44 pm
Barometric Pressure: 1004.6 hPa falling quickly. 1005.1hPa falling quickly.      1005.9 hPa falling.  1008 hPa stable.
Altitude : 93 m (305 ft).                                         89 m (292 ft).                                not recorded              66 m (216.5 ft).
Wind average speed: 1 kph (0.62 mph).           1 kph (0.62 mph).                         1.2 kph(0.74 mph).   1.4 kph (0.86 mph).
Temperature: 20.8 C (69.4 F).                            22.4 C (72.3 F).                            17.2 C (62.9 F).         16.5 C (61.7 F).          
Chill: 21 C (69.8 F).                                              22.4 C  (72.3 F).                           17.2 C (62.9 F).         11.5 C (52.7 F).
Relative Humidity: 60.8%                                     56.1%                                             73.5%.                        82.1%.
Heat Index: 20.9 C (69.4 F).                                 22.3 C (72.1 F).                            16.9 C  (62.4 F).        16.5 C (61.7 F).
Dew Point: 13 C (55.4 F)                                     13.2 C (55.7 F).                            12.5 C (54.5 F).         13.4 C (56.1 F).
Wet Bulb: 16.1 C (60.9 F).                                   16.6 C (61.9 F).                             14.3 C (57.7 F).        14.7 C (58.4 F).

Due to the changing altitude on the unit, I did another GPS reading at my home co-ordinates to ascertain what elevation my home sat at this time. The last time I did it was 3 m (9.8 ft). The GPS gave a reading of 11 m (36 ft). The more I thought about it taking into consideration the slope towards the river, the more I thought this was probably a more accurate measurement. I then adjusted the reference altitude by bringing up the barometric pressure screen. I then simultaneously pressed the two arrow buttons. This brought up the altitude. I then used one of the arrow buttons to advance to 11. To exit, I pressed both arrow buttons simultaneously.

A few days later, I took the unit to a work location about 20 km (12.5 mi) away. I switched the unit on at home and I scrolled to see what the elevation reading was. I was surprised to see a reading of -4 m (-13 ft). I knew that I was not below sea level.
These were the readings that I recorded:
Time: 7.27 am                                                       7.50 am (at work location).            10 am (at work location).         10.33 (home).
Barometric Pressure: 1017.4 hPa stable.          1015.2 hPa stable.                         1014.2 hPa falling.                   1016.2 hPa stable.
Altitude: -4 m (-13 ft).                                             16 m (52 ft).                                     23 m (75.4 ft).                             6 m (19.6 ft).
Temperature: 22.8 C (73 F).                                 24.3 C (75.7 F).                              24.5 C (76.1 F).                        26.5 C (79.7 F).
Relative Humidity: 65.4%.                                     60.9%.                                             52.7%.                                         45.9%.

It is interesting to see that my home location altitude reading varied between -4 m (-13 ft) and 6 m (19.6 ft) over a space of 3 hours and the work location, which is flat, also had a variation of 7 m (23 ft) in the space of 2 hours.

To see if I can rectify the situation, I will do a barometric pressure alteration through the altitude screen after I obtain it from the Bureau of Meteorology. I will report on this in the Long Term Report.

Having a few idle moments, I had a go at removing the impeller unit. I was able to remove it very easily. I pressed firmly on the sides of the impeller housing and it slid out. To replace it was just as easy. I did not have to use much force at all.

Findings to date
The Impeller is extremely quiet. I am not even aware it is rotating unless I am looking at the blades. The sapphire bearings do an excellent job.
I do need to use my glasses to read the small symbols accompanying the measurements. Usually I have a very good idea what the symbols are without my glasses as I am now very familiar with the progressive order when scrolling through the menu.
The display at night is easy to read also. The background light is a nice green glow that does not overshadow the numerals and symbols.
There is no facility to store any data to retrieve at a later date. I have to record the information on the spot so to speak.
I find it very easy to switch between functions. It is just a matter of pressing either the left or right arrow buttons depending on what direction I want to go to reach a unit of measurement that is closest to the current one on display. Sometimes I just use the right arrow button and scroll through all of the units until I find the one I want.
The unit feels very good in my hand and I really appreciate the curved groove on the back which accommodates my index finger. This arrangement lets me operate the buttons with my thumb quiet easily and it is a one handed operational unit.
I found the instruction sheet very easy to understand and I did not have to have an understanding of physics. The instruction sheet gives an explanation of what each unit of measurement means in plain English.
To date I have not had to replace the battery.
I have not noticed any confusion by the unit in reversing the heat index and wind chill index.
When I take a temperature and relative humidity reading, I have to wait for over a minute for the readings to settle down. The display usually goes through a cycle of rising, falling and the rising again before settling on a reading. This is especially noticeable on the temperature unit as this is one I use a lot. The other aspect when using the unit I have to be aware of is the background location when I am taking a reading. I avoid paved areas and courtyard type enclosures and outdoor tables as the give off reflected heat that distorts the true atmospherics.
By way of example, I took a temperature reading in my courtyard by resting the unit on the outdoor table and got a temperature reading of 56 C (133 F). I knew this to be wrong so I went to an open area with lawn and held the unit at waist height. The temperature reading was then 35 C (95 F) which was about right. It was a warm day that was why I wanted to find out the temperature.
To date the unit has not suffered any mishap as it has not been dropped, knocked or mishandled. It is still in perfect good working order.

This concluded my Field Report. The Long Term Report should be completed by March 2007. Please check back then for further information.

LONG TERM REPORT
DATE: 26th February, 2007
My testing locations have been on the Coastal Plain Trail and the Avon Valley, north and north east of Perth and around the metropolitan area when I have been out geocaching. The altitude ranged from 10 metres to 270 metres (33 ft to 885.8 ft). As it is summer, the temperatures have been ranging from overnight lows of 18.9 C (66 F) to daytime highs in the high 30's C + (99 F +) with a recorded maximum by me with the unit of 43.2 C (108 F).
Since my last report I have been able to locate a topological map showing the height of my house. It sits right on the 10 metres (33 ft) contour line showing on the map. I adjusted the setting from 3 metres ( 9.8 ft) to the new setting of 10 metres (33 ft). Sadly, I have to report that the "Altitude" function of this unit never got my home altitude correct. It got close only once, 13 metres (42.6 ft). The height varied between 13 metres ( 42.6 ft) and 103 metres (338 ft). The barometric pressure for the 13 metres (33 ft) was 1015.3 hPa and steady and for the 103 metres (338 ft) 1004.4 hPa with the air pressure falling quickly. At 28 metres (91.8 ft) the air pressure was 1013.2 hPa and steady and at 72 metres (236 ft) the air pressure was 1008.2 and steady.
Out in the field the "Altitude" never matched the maps but it did get very close on one occasion. The unit showed an altitude of 275 metres (902 ft), my GPS showed 273 metres (895.6 ft) and the position on the map was 270 metres (885.8 ft). The barometric pressure was 984.1 hPa and rising. This was the only function that I could not rely on as it worked on air pressure. Not that it mattered as I was not climbing hills in adverse cold weather conditions. I certainly did not rely on it to try and pinpoint my height on a topological map. I placed more reliability on my GPS.
When I went camping to Moore River, I went down to the edge of the Indian Ocean and held the Kestrel about 40 mm (1.5 in) above the water. The altitude reading came in at 23 metres (75 ft) and the barometric pressure was 1013 hPa and rising.
This summer we went onto Daylight Savings where we had to put the clock forward by an hour so I did the necessary clock adjustment which was very easy.
Many weeks later after adjusting the time, I checked the time against the official time. The clock had lost three minutes in about eleven weeks since I received the unit for whatever reason. I have not had to change the battery, so I have not interfered with the electrical circuitry.
The display screen is showing fine vertical scratch lines. I suspect  that the slide on and off cover is the culprit. The fine lines do not interfere with the display in any way at all.
One very useful function is the "Hold" mode. I use this regularly so that I can get a snap shot at a given point in time to record the measured values of the unit, especially when I go indoors or in a shady spot to record the data. To achieve this I press the centre button and the left arrow button at the same time. When I want to vacate the "Hold" mode I just repeat the same button pushing exercise.
I like to do some of my testing at a campsite on the Coastal Plain Trail as it is about 6 km (3.7 mi) from a weather station so I had a good reference to verify my readings from the unit. The weather station sits at an elevation of 40 metres (131 ft) and where I camp sits at an elevation of 83 metres (272 ft). I cannot see the weather station due to dense bush even though I am at a higher elevation.
By way of comparison I have set out a sample of my readings and the Pearce RAAF Base weather station which is the closest weather station to where I have been camping.

Sunday 14 th January, 2007
                                                         Time              Temperature         Relative Humidity        Dew Point          Barometric Pressure
My recordings                                 10.30 am       36.6 C (97.9 F)         31%                           16.7                  1008.2 steady
                                                            2.00 pm       43.2 C (109.7 F)       37%                           25.2                  1005.6 falling
                                                            3.00 pm       39.9 C (103.8 F)       25.5%                       16.5                   1005.1 falling
                                                            6.00 pm       32.2 C (89.9 F)         32.9%                       13.8                    1005.0 steady

Pearce RAAF base                       10.30 am        35.9 C (96.6 F)         17%                           7                        1008.5 steady
                                                            2.00 pm        41 C    (105.8 F)         8%                           0.9                     1005.4 falling
                                                            3.00 pm        37.2 C (98.9 F)          22%                        11.8                     1005.2 falling
                                                            6.00 pm        31.9 C (89.4 F)          30%                        12.4                     1005.4 steady

From the above sample of readings, the Kestrel 3500 came very close to the official weather bureau's readings. I put the big difference of the Dew Point down to the fact that the air force base is lower down than I was and it is located on a big flat plain. The open flat location would also have an effect on the Relative Humidity. However, as it got a bit cooler towards the evening, the Relative Humidity at the air base crept up close to my readings.

The author recording readings

SUMMARY
Overall, I am impressed with the Kestrel 3500 as it records the weather conditions that are within the ballpark of the weather stations close by, so I am confident that ten out of eleven units of measure, leaving aside the clock, can be relied upon. The only unit of measure that disappointed was the altitude readings.
Just on a normal everyday situation I found that my wife and son would grab the unit a number of times during the day to see how hot it was and then be generous in their praise to see that it came up with the same answer as the weather report on the T.V. news of an evening for the maximum. As an aside, they were not up early enough to record the minimum. I also used to take it out during the day when at work in the field and do the same thing, but I would also check it against the weather bureau's web page for the day that gives an hourly breakup with many units of measure.
I found that I had to wait under two minutes with the unit switched on before it settled down to the true unit of measurement as verified by the weather bureau station nearby. One very good example of this is the temperature unit. When it is first switched on there is a flurry of numerals coming and going on the screen. I wait until this movement of numerals settles down and I might get a small variation in the reading of well under 1C (1.8 F). I usually wait until it hits its peak and then drops back slightly by a fraction of a degree. If a puff of wind comes along the temperature has a small downward change straight away even though it still feels hot on my skin, so I tended to find a sheltered spot to take my readings. Occasionally the readings were ready under a minute in line with the manufacturers specifications but on occasions I did tend to err on the side of caution and wait a bit longer.

Additional Things I like

• Very good accuracy for all of the units of measure except for Altitude.
• Have not had to change the battery after approximately four months of continuous use.
• Has a wow factor. Everybody who has seen it wants to borrow it and use it, within my sight I might add. Due to our hot weather they all want to know how hot it is.
• Has stood up to the rigours of being pulled in and out of a backpack, hung around my neck when climbing a scrubby hill and accidentally dropped (with the case on).
  

• Very fine vertical line scratching on the display window caused by the cover sliding on and off.
• Cannot rely on the altitude reading.

Reviews > Environmental Monitoring Gear > Weather Recorder > Kestrel 3500 > Ralph Ditton > Test Report by Ralph Ditton