Davis Instruments GroWeather, GroWeather 7450, GroWeather 7455 User Manual

G

RO

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EATHER

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YSTEM

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ONSOLE

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SER

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M

ANUAL

Product # 7450 & 7455

Product Numbers: 7450/7455

Davis Instruments Part Number: 7395-070
GroWeather™ Console, Standard & Industrial
Rev. C Manual (7/16/99)
This product complies with the essential protection requirements of the
EC EMC Directive 89/336/EC.

© Davis Instruments Corp. 1997. All rights reserved.

GroWeather™ is a trademark of Davis Instruments Corp.
WeatherLink

®

is a registered trademark of Davis Instruments Corp.

Windows™ is a trademark of Microsoft Corp.

G

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YSTEM

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ONSOLE

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ANUAL

Page i GroWeather Manual

T

ABLE OF

C

ONTENTS

I

NTRODUCTION TO THE GROWEATHER SYSTEM

. . . . . . . 1

O

PTIONAL

S

ENSORS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

O

PTIONAL

A

CCESSORIES

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

G

RO

W

EATHER

S

YSTEM

O

VERVIEW

. . . . . . . . . . . . . . . . . 5

T

HE

K

EYBOARD

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

W

EATHER

C

ONDITIONS

M

EASURED

/C

ALCULATED

. . . . . . . . . . . . . 6

EvapoTranspiration (ETo) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Growing Degree-Days (Heat Units) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Air, Soil, and Apparent Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Wind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Solar Radiation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Rainfall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Barometric Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Relative Humidity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Dew-Point & Leaf Wetness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

P

ERIOD

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

A

UTO

C

LEAR

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

H

IGHS

AND

L

OWS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

A

LARMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

U

SING

THE

G

RO

W

EATHER

. . . . . . . . . . . . . . . . . . . . .17

U

SING

THE

E

NTER

K

EY

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Entering Negative Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Example of Using ENTER: Setting the Time . . . . . . . . . . . . . . . . . . . . . . 18

E

VAPO

T

RANSPIRATION

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Viewing ETo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Selecting Units of Measure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Clearing Daily ETo Sum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

G

ROWING

D

EGREE

-D

AYS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Viewing Degree-Days . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Selecting Units of Measure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Setting Thresholds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Clearing Daily Degree-Days Sum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Table of Contents Page ii

A

IR

, S

OIL

,

AND

A

PPARENT

T

EMPERATURE

. . . . . . . . . . . . . . . . . . 25

Viewing Air and Soil Temperature, T-H Index, and Wind Chill . . . . . . . .25

Selecting Units of Measure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

High and Low Air and Soil Temperature, T-H Index, and Wind Chill . . . 27

Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

W

IND

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

The Compass Rose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28

Viewing Wind Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Selecting Units of Measure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

High Wind Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30

Clearing Daily Wind Run . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

S

OLAR

R

ADIATION

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Viewing Solar Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Clearing Daily Solar Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

R

AINFALL

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Viewing Rainfall. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

Selecting Units of Measure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Entering Total Rainfall. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

High Rate of Rainfall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Clearing Daily and Total Rainfall. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

B

AROMETRIC

P

RESSURE

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Barometric Trend Indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35

Viewing Barometric Pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Selecting Units of Measure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Entering Barometric Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Displaying Stored Barometric Pressure . . . . . . . . . . . . . . . . . . . . . . . . . .37

Storing Barometric Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

R

ELATIVE

H

UMIDITY

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Viewing Humidity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

High and Low Relative Humidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

D

EW

-P

OINT

AND

L

EAF

W

ETNESS

. . . . . . . . . . . . . . . . . . . . . . . . 39

Viewing Dew-Point and Leaf Wetness. . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Selecting Units of Measure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Alarms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Page iii GroWeather Manual

T

IME

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Displaying Time Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Selecting Display Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Entering Time, Date, or Year . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Setting the Time for AutoClear. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Clearing Period Information/Starting a New Period . . . . . . . . . . . . . . . . 44

H

IGHS

AND

L

OWS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Displaying Highs and Lows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Clearing Highs and Lows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

A

LARMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

The Alarm Display. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Viewing an Alarm Threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Setting a Normal Alarm Threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Example of Setting an Alarm Threshold: Low Outside Air Temperature Alarm
48

“Daily” ETo Alarm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Setting the Barometric Pressure Alarm. . . . . . . . . . . . . . . . . . . . . . . . . . 49

Setting the Dew-Point Alarm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

To Silence an Alarm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

To Clear an Alarm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

E

NABLING

/D

ISABLING

A

UTO

C

LEAR

. . . . . . . . . . . . . . . . . . . . . . 51

G

ENERAL

H

IGH

/L

OW

C

LEAR

. . . . . . . . . . . . . . . . . . . . . . . . . . . 51

To Use General Clear Feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

D

ISPLAY

S

CAN

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Starting the Scan Routines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Stopping a Scan Routine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

C

ALIBRATION

N

UMBERS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Inside and Outside Temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Humidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Wind Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Rainfall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Changing Calibration Numbers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Resetting Calibration Numbers to Default . . . . . . . . . . . . . . . . . . . . . . . 54

P

RIMARY

P

OWER

AND

B

ATTERY

B

ACKUP

I

NDICATORS

. . . . . . . . . 55

Table of Contents Page iv

GroWeather Manual Page 1

Chapter

1

I

NTRODUCTION TO

THE

G

RO

W

EATHER

S

YSTEM

For gardeners, growers, forestry or public-safety agencies, golf course manag­ers, parks departments, and commercial landscape managers, the GroWeather
system (simply referred to as “GroWeather” in this manual) measures environ­mental conditions which affect plant, pest, and livestock development. This
integrated weather station and data logger measures/calculates, displays, and
stores wind speed and direction, wind run, solar radiation, solar energy, air
temperature, temperature/humidity index and wind chill (apparent tempera­ture), growing degree-days, soil temperature, humidity, dew-point, leaf wet­ness, barometric pressure, evapotranspiration, rainfall, and rate of rainfall.
Current readings, high and low readings, cumulative totals, and “daily” aver­ages are available for display at the push of a button. Degree-day thresholds
(both lower and upper) can be set by the user. The system can sound an alarm
when values exceed a threshold set by the user.

This information enables the grower or turf manager to plant, irrigate, and con­trol pests with high efficiency. It enables the forester or fire department to mon­itor fuel and wind conditions. It also gives a measure of environmental stress
on workers and livestock.

Introduction to the GroWeather System

Page 2 GroWeather Manual

O

PTIONAL

S

ENSORS

The following optional sensors enable the GroWeather to measure and calcu­late specialized weather information. All optional sensors are available from
your dealer or may be ordered directly from Davis Instruments.

• Anemometer

Enables you to measure and display wind speed, wind direction, wind
chill (with temperature sensor), and wind run. Also required for calcu­lating ET.

• External Temperature Sensor

Enables you to measure and display air temperature and growing
degree-days or soil temperature.

Note: You may only use two of the following sensors at a time on your GroWeather: External Tem-

perature Sensor, External Temperature/Humidity Sensor, Stainless Steel Temperature Probe,
or Leaf Wetness Sensor.

• External Temperature/Humidity Sensor

Enables you to measure and display air temperature, humidity, growing
degree-days, temperature-humidity index, and dew-point. (See note in
external temperature section for restrictions.)

• Leaf Wetness Sensor

Enables you to measure and display the surface moisture on foliage. (See
note in external temperature section for restrictions.)

• Rain Collector

Enables you to measure and display daily and yearly rainfall and rate of
rainfall. Separate models measure rainfall in either 0.01-inch or 0.2-mm
increments. Optional Rain Collector Heater enables you to measure the
moisture content of snowfall or freezing rain.

• Solar Radiation Sensor

Enables you to measure and display solar irradiance and incident
energy. Also required for calculating ET.

• Stainless Steel Temperature Probe

Enables you to measure and display air temperature and growing
degree-days or soil temperature. Rugged stainless-steel construction
makes sensor ideally suited to measuring soil or water temperature. (See
note in external temperature section for restrictions.)

O

PTIONAL

A

CCESSORIES

The following accessories, designed for use with the GroWeather, are available
from your dealer or may be ordered directly from Davis Instruments.

• GroWeatherLink

®

ET/Data Logger

Performs ETo calculations and logs data for use with GroWeatherLink
Software.

Optional Accessories

GroWeather Manual Page 3

• GroWeatherLink Software

Logs data gathered by the GroWeather, downloads it to your PC, and
generates reports and graphical displays. Storage interval (1, 5, 10, 15, 30,
60, or 120 minutes) is set by the user. The data logger will store 16 hours
or 3, 7, 10, 21, 42, or 85 days worth of data depending on storage interval.
Windows

™

-compatible software enables you to analyze, plot, print, sort,
and summarize the data. Calculate, view, and print crop or pest-specific
degree-day totals. Automatically generates NOAA reports. Also
includes an advanced crop water management (ETc and irrigation) fea­ture. Requires GroWeatherLink ET/Data Logger, Windows 3.1 or Win­dows 95, and one free serial port.

• Sensor Mounting Arm

A single-location mounting option. The Sensor Mounting Arm includes
provisions for optimal mounting of all Davis sensors: anemometer, tem­perature sensor (with Radiation Shield), Solar Radiation Sensor, Rain
Collector Shelf, etc.

• Radiation Shield

Protects the temperature sensor or temperature/humidity sensor from
solar radiation and other sources of radiated and reflected heat.
Increases the life of the sensor and the accuracy of the readings.

• Shelters

Two weather-resistant shelters enable you to mount some or all of your
system components outside. Optional heaters enable you to keep com­ponents operating even in cold weather.

• Solar Power Kit

Powers the weather station using energy from the sun; no AC power is
required. Requires our 6.5-Amp-Hour Battery or other battery of your
choice.

• Alarm Output Module

Enables you to use weather station alarms to automatically start or stop
external devices such as irrigation systems, heaters, or fans.

• Surge Protectors

For upgraded protection against lightning-induced power surges,
power-cross conditions, and ground potential rises, use Surge Protec­tors. Use one Surge Protector for every two wires and mount inside one
of our surge-protector shelters.

Introduction to the GroWeather System

Page 4 GroWeather Manual

GroWeather Manual Page 5

Chapter

2

G

RO

W

EATHER

S

YSTEM

O

VERVIEW

THE K

EYBOARD

The GroWeather’s keyboard contains two types of keys: function keys and
operation keys. The larger and more square keys (e.g., TEMP, RAIN, WIND)
are the function keys and are used to display the various conditions measured
and calculated by the GroWeather. The smaller and more rounded keys (e.g.,
Enter, Units, Alarm) are operations keys and are used to view or use the vari­ous features of the GroWeather.

GroWeather System Overview

Page 6 GroWeather Manual

W

EATHER

C

ONDITIONS

M

EASURED

/C

ALCULATED

This section outlines each of the weather conditions measured/calculated by
the GroWeather. Each section includes a brief discussion of the weather condi­tion and a listing of the various ways in which the unit displays or stores that
condition. Be aware that some of the weather conditions require an optional
sensor in order to measure/calculate a value (see “Optional Sensors” on
page 2).

Values which are described as “Daily” readings will provide true daily read­ings only if they are cleared each day. You may clear these values yourself or
use AutoClear (see “AutoClear” on page 13) to clear them for you. If you do
not clear the values every day, you may use the “daily” readings to represent
any interval you desire: two days, one week, one month, etc. See “Period” on
page 12 for information on readings which are described as being for the
“period.”

The notation “(AutoClear)” next to a weather condition indicates that the
GroWeather’s AutoClear function may clear the weather condition at a set time
every day. For information on AutoClear, see “AutoClear” on page 13.

The notation “(Alarm:)” next to a weather condition indicates that an alarm
exists for the weather condition. The type of alarms are noted after the colon.
For information on Alarms, see “Alarms” on page 14.

EvapoTranspiration (ETo)

EvapoTranspiration (ETo) is a measurement of the amount of water vapor
returned to the air in a given area. It combines the amount of water vapor
returned through evaporation (from wet vegetation surfaces and the stoma of
leaves) with the amount of water vapor returned through transpiration (exhal­ing of moisture through plant skin) to arrive at a total for the area. Effectively,
ETo is the opposite of rainfall, and it is expressed in the same units of measure
(Inches, millimeters).

The GroWeather uses air temperature, relative humidity, wind run, and solar
radiation data to estimate ETo, the reference evapotranspiration based on a
standard turf model. The actual ETo calculations are performed by the
GroWeatherLink ET/Data Logger . (ETo is calculated once an hour on the hour.)
To calculate and display crop-specific ETc, you will need the GroWeatherLink
Software as well. See “Optional Accessories” on page 2 for more details.

• “Daily” ETo Sum (AutoClear) (Alarm: High)

• Total ETo for the period (Alarm: High)

• Average ETo per day over the period

Weather Conditions Measured/Calculated

GroWeather Manual Page 7

Growing Degree-Days (Heat Units)

Because temperature plays an important part in the rate of development of
plants and many pests (especially insects) a measurement which takes into
account the accumulation of heat with passing time is necessary to predict mat­uration. Growing degree-days provide a measure for calculating the effect of
temperature on the development of plants and/or pests. One degree-day is the
amount of heat which accumulates when the temperature remains one degree
above the base developmental threshold (base threshold) for 24 hours. One
degree day is also the amount of heat which accumulates when the temperature
remains 24˚ above the base threshold for 1 hour.

In order to use degree-days effectively, you must know the developmental
threshold(s) for the desired crop or pest. The base developmental threshold is
the temperature at and below which development stops. Above the base
threshold development increases until temperature reaches the upper thresh­old, over which development rate decreases.

Note: The GroWeatherLink Software enables you to calculate, display, and print crop and pest-specific

degree-day totals. See “Optional Accessories” on page 2 for more details.

Unlike strict time predictions of plant/pest development, degree-day predic­tions hold true regardless of location or temperature fluctuations. As long as
you know the number of degree-days necessary for plant/pest development,
you may use degree-days as an accurate predictor. For example, you may
know that it takes, in general, three weeks for a specific pest to develop. What
you will find, however, is that the pest may take 4 weeks to develop in cooler
weather and only 2 weeks to develop in warmer weather. The time prediction
can be off by up to a week in this example, while the degree-day prediction
should result in far greater accuracy.

The GroWeather uses the temperature reading in conjunction with the base and
upper thresholds which you set (see “Setting Thresholds” on page 24) to calcu­late degree-days. The GroWeather keeps a running total of the accumulating
“degree-minutes” and “degree-seconds” to provide the most accurate degree­day information possible. Keep in mind that local variations in terrain, vegeta­tion, and elevation can make a significant difference in temperature readings,
so you should endeavor to place the temperature sensor in the same location as
the plant/pest.

• “Daily” Degree-Days Sum (AutoClear)

• Total Degree-Days for the period (Alarm: High)

• Average Degree-Days per day over the period

GroWeather System Overview

Page 8 GroWeather Manual

Air, Soil, and Apparent Temperature

The GroWeather uses the primary temperature sensor to measure the outside
air temperature. The second temperature sensor can be used to measure the
soil temperature or to measure the air temperature in a second location.
Although it is referred to as “soil” temperature, you may use this sensor to
measure whatever auxiliary temperature you see fit (including water tempera­ture). In addition, the GroWeather calculates two apparent temperature read­ings: temperature/humidity index (T-H Index) and wind chill.

The T-H Index uses the temperature and the relative humidity to determine
how hot the air actually “feels.” When humidity is low, the apparent tempera­ture will be lower than the air temperature since perspiration can rapidly evap­orate into the air. However, when humidity is high (i.e., the air is saturated
with water vapor) the apparent temperature will be higher than the air temper­ature.

Note: The GroWeather measures T-H Index only when air temperature is above 68˚ F (20˚ C) because it

is a measure of heat stress, which is not significant at lower temperatures. 125˚ F (52˚ C) is the
highest T-H Index for which calculation factors are available. Above that, the system simply reports
that T-H Index is “high.”

Wind chill takes into account how the speed of the wind affects our perception
of the air temperature. The body warms up the air molecules which surround it
by transferring heat from the skin to the surrounding air. If the wind is com­pletely still, this “insulating layer” of warm air molecules stays next to the
body, offering some protection from the cooler air molecules and limiting fur­ther transfer of heat. When the wind is blowing, however, the warm air sur­rounding the body is swept away. The faster the wind blows, the faster the heat
is carried away and the colder you feel.

• Current Outside Air Temperature (Alarm: High/Low)

• Current Soil Temperature (Alarm: High/Low)

• Current Temperature/Humidity Index (Alarm: High)

• Current Wind Chill (Alarm: Low)

• “Daily” High and Low Air Temperature with time and date of occurrence (Auto­Clear)

• “Daily” High and Low Soil Temperature (AutoClear)

• “Daily” High Temperature/Humidity Index with time and date of occurrence
(AutoClear)

• “Daily” Low Wind Chill with time and date of occurrence (AutoClear)

Weather Conditions Measured/Calculated

GroWeather Manual Page 9

Wind

The GroWeather measures wind speed, wind direction, and wind run. Wind
run is a measurement of the “amount” of wind which passes a given point (the
anemometer) during the measurement period. It is expressed as either “miles
of wind” or “kilometers of wind” and is determined by calculating the integral
(summation) of wind speed multiplied by the time of the measurement period.
For example, if the wind blew at an absolutely steady 10 MPH for 12 hours,
you would have 120 miles of wind run (speed x time = 10 MPH x 12 Hours =
120 miles). Wind speed changes over time, so wind r un is calculated by adding
together (summing) the distance (speed x time) for every single speed and time
reading during the measurement period. In practice, however, the GroWeather
simply keeps count of the number of revolutions made by the wind cups dur­ing the period and multiplies that number by a scale factor which gives a wind
run reading in either miles or kilometers.

• Current Wind Speed (Alarm: High)

• “Daily” Wind Run (AutoClear)

• Average Wind Run per day during period

• Wind Direction

• High Wind Speed with time and date of occurrence and direction of high (Auto-

Clear)

Solar Radiation

What we call “current solar radiation” is technically known as Global Solar
Radiation, a measure of the intensity of the sun’s radiation reaching the earth’s
surface. This irradiance includes both the direct component from the sun and
the diffuse component from the rest of the sky. The solar radiation reading
gives a measure of the amount of solar radiation hitting the solar radiation sen­sor at any given time, expressed in Watts per Square Meter (W/m

2

). The power
of this radiation, when integrated (summed) over a period of time, gives a
measure of the amount of incident solar energy received during that time
period. This solar energy reading is expressed in Langleys.

Note: The GroWeather measures energy received in the spectral band between 400 and 1100 nm.

• Current Solar Radiation Intensity

• “Daily” Incident Solar Energy Sum (AutoClear)

• Average Incident Solar Energy per day during period

1 Langley = 41.84 kiloJoules per square meter

= 11.622 Watt-hours per square meter
= 3.687 BTUs per square foot

GroWeather System Overview

Page 10 GroWeather Manual

Rainfall

The GroWeather provides two separate registers for tracking rainfall totals.
One is referred to as “daily” rainfall and the other is referred to as “total” rain­fall. In truth, these registers can be used to record rainfall over any period of
time you desire. The “daily” register can be cleared daily using the AutoClear
function (see “AutoClear” on page 13) to provide true daily rainfall totals or
you may clear it manually every few days, after a storm, at the end of the
month, etc. The total rainfall amount must be cleared manually; how often you
clear the register determines what period of time its rainfall total reflects. The
GroWeather also calculates the rate of rainfall by measuring the interval of time
between each .01” or .2 mm rainfall increment.

• “Daily” Rainfall (Alarm: High) (AutoClear)

• Current Rate of Rainfall in inches or millimeters per hour

• Total Rainfall

• High Rate of Rainfall with time and date of occurrence (AutoClear)

Barometric Pressure

The weight of the air which makes up our atmosphere exerts a pressure on the
surface of the earth. This pressure is known as atmospheric pressure. Gener­ally, the more air above an area, the higher the atmospheric pressure, which
means that atmospheric pressure changes with altitude. To compensate for this
difference and facilitate comparison between locations with different altitudes,
atmospheric pressure is generally adjusted to the equivalent sea-level pressur e.
This adjusted pressure is known as barometric pressure. In reality, the
GroWeather measures atmospheric pressure. When you enter the barometric
pressure for your location (see “Entering Barometric Pr essur e” on page 37), the
GroWeather stores the necessary offset value to consistently translate atmo­spheric pressure into barometric pressure.

Barometric pressure also changes with local weather conditions, which makes
barometric pressure an extremely important and useful weather forecasting
tool. High pressure zones are generally associated with fair weather while low
pressure zones are generally associated with poor weather. For forecasting pur­poses, however, the absolute barometric pressure value is generally less impor­tant than the change in barometric pressure. In general, rising pressure
indicates improving weather conditions while falling pressure indicates deteri­orating weather conditions.

• Current Barometric Pressure (Alarm: rate of change)

• Recall of Previously Stored Barometric Pressure Value, with time and date of
stored value (AutoClear)

• Trend of Barometric Pressure (rising, falling, steady) over previous one hour

Weather Conditions Measured/Calculated

GroWeather Manual Page 11

Relative Humidity

Humidity itself simply refers to the amount of water vapor in the air. However,
the amount of water vapor which the air can contain varies with air tempera­ture and pressure. Relative humidity takes into account these factors and of fers
a humidity reading which reflects the amount of water vapor in the air as a per­centage of the amount the air is capable of holding. Relative humidity, there­fore, is not actually a measure of the amount of water vapor in the air, but a
ratio of the air’s water vapor content to its capacity.

It is important to realize that relative humidity changes with temperature, pr es­sure, and water vapor content. A parcel of air with a capacity for 10 g of water
vapor which contains 4 g of water vapor, the relative humidity would be 40%.
Adding 2 g more water vapor (for a total of 6 g) would change the humidity to
60%. If that same parcel of air is then warmed so that it has a capacity for 20 g
of water vapor, the relative humidity drops to 30% even though water vapor
content does not change.

Relative humidity is an important factor in determining the amount of evapo­ration from plants and wet surfaces since warm air with low humidity has a
large capacity for extra water vapor.

• Relative Humidity of Outside Air (Alarm: High/Low)

• “Daily” High and Low Relative Humidity reading with time of occurrence (Auto-

Clear)

Dew-Point & Leaf Wetness

Dew-point is the temperature to which air must be cooled for saturation (100%
relative humidity) to occur, providing there is no change in water content. The
dew-point is an important measurement used to predict the formation of dew,
frost, and fog. If dew-point and temperature are close together in the late after­noon when the air begins to turn colder, fog is likely during the night. Dew­point is also a good indicator of the air’s actual water vapor content (as
opposed to relative humidity). High dew-point indicates high vapor content;
low dew-point indicates low vapor content. You can even use dew-point to
predict the minimum overnight temperature. Provided no new fronts are
expected overnight, the afternoon’s dew-point gives you an idea of what mini­mum temperature to expect that night, since the air is not likely to get colder
than the dew-point anytime during the night.

Leaf wetness provides an indication of whether the surface of foliage in the
area is wet or dry by indicating how wet the surface of the sensor is. The leaf
wetness reading ranges from 0 (dry) to 15.

• Current Dew-Point (Alarm: when temperature is within 2˚F of dew-point)

• Leaf Wetness

GroWeather System Overview

Page 12 GroWeather Manual

Time

The GroWeather has a clock and a calendar for tracking time and date. The cal­endar automatically adjusts during leap years, providing you enter the current
year (see “Entering Time, Date, or Year” on page 43) when you apply power to
the unit.

• Current Time (Alarm: standard)

• Current Date

• Current Year

• Date of Period Start and Number of Days in Period

• AutoClear Time Setting

P

ERIOD

The GroWeather uses a single time period for all values which accumulate
totals or calculate daily averages over an interval. Beginning a new period
clears all data from the previous period. The system stores the beginning date
of the period, which you may display along with the number of days which
have elapsed since the beginning of the period.

Note: The system records the start time of the period to the nearest 90 minutes. Therefore, all average val-

ues are exact to the nearest 90-minute mark throughout the period. However, averages calculated
during the period are most accurate when the period length is an exact number of days (that is, if
you display the average at the same time of day at which the period started). When the length of the
period is displayed, the GroWeather rounds down to the nearest whole day COMPLETED.

The following values are accumulated or averages calculated during the
period. Note that averages are not displayed (a series of dashes appears
instead) until at least one day has elapsed.

• Total ETo

• Average ETo per day

• Total Degree-Days

• Average Degree-Days per day

• Total Wind Run

• Average Wind Run per day

• Average Incident Solar Energy per day

AutoClear

GroWeather Manual Page 13

A

UTO

C

LEAR

The GroWeather’s AutoClear function may be used to automatically clear
some or all of the “daily” values at the same time each day. The time at which
values are cleared is the same for all values and may be set by the user (default
is midnight). The AutoClear function may be enabled/disabled individually
for the values listed below. Note that the AutoClear function for some values
(for example, high wind speed and “daily” wind run) is linked; you may
enable or disable the AutoClear for all linked values, not for each individual
value. The list below shows all values which may be cleared using AutoClear.
Those listed together must be cleared as a group.

• “Daily” ETo Sum

• “Daily” Degree-Days Sum

• High and Low Air Temperature, High and Low Soil Temperature, High Tempera-

ture/Humidity Index, Low Wind Chill

• High Wind Speed and “Daily” Wind Run

• “Daily” Incident Solar Energy Sum

• “Daily” Rainfall and High Rate of Rainfall

• High and Low Relative Humidity

H

IGHS

AND

L

OWS

The GroWeather records highs and lows for many weather conditions. All
highs and lows represent the maximum or minimum reading since the last
time you cleared each individual high/low register. If you have enabled the
AutoClear for a particular high/low (see “Enabling/Disabling AutoClear” on
page 51), this reading will represent the high/low since the time of the Auto­Clear. In other words, it will track highs and lows over a 24 hour period. If you
do not use AutoClear, you may track daily, weekly, monthly, or yearly values,
depending on how often you manually clear them.

For most highs and lows, the time and date at which they occurred is stored
along with the value. Please note, however, that the date is only stored as long
as it falls within 14 days of the current date. After 14 days, the GroWeather dis­plays only the high/low reading and the time; the date appears as a series of
dashes.

Note: See “Barometric Pressure” on page 35 for details on the stored barometric pressure.