Spectrum Technologies Field Scout TDR 250 User manual

TDR 250
Soil Moisture Meter
PRODUCT MANUAL
Item # 6250

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Thank you for purchasing the Field ScoutTM TDR 250
soil moisture meter. This manual describes the meter's
general features and operation.
Soil moisture is a critical, and potentially highly varia-
ble, component of the soil environment. Time domain
reflectometry is a proven technology for quickly and
accurately determining volumetric water content
(VWC) in soil. Electrical conductivity (EC) is a func-
tion of the moisture and salt in the soil and can be fac-
tored out to increase the accuracy of VWC measure-
ments. The meter also measures soil surface tempera-
ture. The user can quickly transition between taking
VWC readings in standard, high-clay, and sand soils.
The TDR 250’s shaft-mounted probe allows the user to
take measurements while standing. The meter’s built-in
data logger eliminates the need to record data manually.
Measurements can be saved to a USB flash drive using
the built-in USB port.
Contents
Includes the following components:
- TDR 250 meter
- 4 AA batteries already installed
Note: TDR rods are sold separately
General overview
This manual will familiarize you with the features and operation of
your new Field ScoutTM TDR 250 Soil Moisture Meter. Please read
this manual thoroughly before use

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CONTENTS
General Overview 2
Specifications 4
Product Dimensions 5
Meter Care 6
Button Functions 7
Meter Operation 8
Display Screens 9
Setting the Date/Time 12
Maintenance 13
Data Logs 14
VWC Measurements 15
Optional Accessories 16
Appendix 1: Soil Specific Reading Correlation 17
Appendix 2: Troubleshooting 18
Appendix 3: Updating Device Firmware 19
Appendix 4: Calibration 20
Glossary 21
CE Declaration of Conformity 22
UK Declaration of Conformity 24
FCC, ISED, and other Regulatory Information 26
Warranty 28

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Measurement
Units
Percent volumetric water content (VWC)
Period (raw sensor reading)
Resolution,
Accuracy and
Range
VWC: 0.1% increment ±3.0% @ < 2 mS/cm
0% to Saturation (Saturation is typically around
50% volumetric water)
Connectivity USB Type A port for USB Flash Drives
Power 4 AA alkaline batteries
Log Capacity Up to 124,000 measurements
Display Backlit, high-contrast, graphic LCD
Weight 4.3 lbs. (1.9 kg)
IP Rating Display: IP53, Probe: IP67
Available
Rod
Dimensions
Turf 1.5” (3.8cm)
Short 3.0” (7.6cm)
Medium 4.8” (12.2cm)
Long 8.0” (20.32cm)
Diameter 0.2” (0.5cm)
Spacing 1.2” (3cm)
Specifications

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Product dimensions

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The FieldScout TDR meter will function properly under normal
conditions experienced in field use. The sensor block is sealed
and will not be damaged by immersion in water. The display is
not waterproof. The meter should not be used during heavy rain-
fall or left exposed during irrigation events. If the display does get
wet, it should be dried out immediately.
Follow these tips to prolong the life of the device:
- Store in a cool and dry place when not in use.
- Keep the meter and probe rods clean and dry in between uses.
- Remove the batteries if not used for an extended period of time
(ie: between seasons).
Battery life
If the battery level is low or a bat-
tery is inserted incorrectly, the
low battery icon appears on the
screen and the display will power
off.
Battery life is affected by the ena-
bled features and frequency of
use. If not needed, the backlight can be disabled or set to AUTO
mode (page 10) which allows enough time to see new measure-
ments and then will power down the backlight to conserve the
battery life.
Meter Care

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Button Functions
ON/OFF or BACK button
− Press briefly to power on.
− Press and hold to power on and stay on the logo
screen.
− Press and hold for 2 seconds to power off.
− Press within a menu to return to prior screen.
MENU or SELECT button
− Press to enter available menus.
− Press to select or confirm a menu selection.
DELETE or UP button
− Press to move up within a menu.
− Delete last measurement from the running aver-
age, counter, and its entry from the internal data
log (see page 14).
READ or DOWN button
− Press to move down within a menu.
− From Reading screen, press to make a reading.
− Press and hold to reset the average and count.

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Meter Operation
Setting up the meter
1. Slide the lock washers onto the threaded ends of the handle
bars.
2. Install the two cushion grip handles and tighten securely.
3. Pull the battery transport tab out of the display unit.
4. Select a set of probe rods and screw them to the bottom of the
probe block. Tighten the rods securely.
5. Set the desired user settings in the settings menu. See page 10.
Taking Readings
1. Grip the TDR handles to the left and right of the display.
2. Push down on the handles maintaining a steady downward
pressure to drive the rods into the soil until the sensor base is in
contact with the soil surface. Refrain from any back and forth or
side to side movement which can introduce air pockets into the
soil medium which will alter the reading accuracy.
Caution: Exercise care not to bend or force the rods which could
lead to damage.
3. Press the READ button and observe the change in results on
the top display.
Figure 1. Handlebars Attached

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Display Screens
The TDR 250 has 3 main display screens:
- Startup Information (shown on page 7)
- Reading (shown below)
- Settings Menu (see page 10)
Startup Information screen
Initially displayed after first powered on.
- Displays firmware version information.
- Press and hold ON/OFF|BACK button to remain on this screen.
Reading screen
Measurements from the sensor are displayed on the Reading
screen along with rod size used, soil type, and a reading count
with running average. VWC=0% readings will be displayed but
will not increment the counter or be included in the average.
Press READ to take readings, update Count and the Average.
The battery level icon appears in the upper right corner.

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Settings Menu screen
Used for changing device features, setting rod length and working
with log files.
Use the arrow buttons to move to the desired option.
The Select button toggles through option choices.
Clear Average*: Clears the displayed average and count.
Note: Same as pressing and holding the READ|Down arrow button
Rod Length: Select the Rod length. See page 4 for options.
Soil Type: Selects soil type used in measurements:
- Standard: for most soil types.
- Hi-Clay: for soils with higher clay content (> 27%).
- Sand: for sand based fields or turf greens.
Clear Logs*: Erases data logs from internal memory.
Save to USB*: Transfers data logs to a USB flash drive if attached.
Backlight: Sets the LCD backlight: ON, OFF, AUTO. In AUTO
mode, the backlight will shut off 5 seconds after a button press
Sound: Enable or disable beep for audible feedback.
Moisture Type: Selects displayed moisture mode VWC%, Period, or
TDR 300.
- VWC%: Volumetric Water Content with EC compensation.
- Period: Raw sensor reading in microseconds (us)
- TDR 300: VWC% without EC compensation
Auto-Off: Power off delay: 15, 30, 45, 60 minutes.
Current Date, Current Time: Displays or set the current time and
date values. See page 12 for details.
Timezone: Offset from Greenwich Mean Time. As the offset changes,
the Time and Date will update.
Daylight Savings: ON or OFF.

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Calibration*: Overrides factory calibration. See Appendix 4
Clear User Calibration: Clears the user applied calibration back to
factory settings
Factory Defaults*: Resets menu settings and counter to the factory
default value.
* Pressing Select button for these options brings up an additional
screen.
About: Displays general information (Model and serial number, firm-
ware versions for display and sensor).
Defaults:
Rod Length None
Soil Type Standard
Sound On
Temperature Fahrenheit
Backlight Disabled
Moisture Type VWC
EC Units mS/cm
Auto-Off 15 minutes
Time Zone GMT

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The Date and Time are displayed in the Settings Menu.
Note: When the batteries are removed, the date and time are re-
set.
Updating the Date and Time
1. Press the MENU|SELECT button to enter the Settings Menu.
2. Press the UP or DOWN arrows to navigate to either the Cur-
rent Date or Current Time option.
3. Press the MENU|SELECT button to access the Time/Date up-
date screen.
4. Press the DELETE|UP button to set the date and time. The
current time for the timezone setting will be displayed.
5. Use the UP and DOWN arrows to adjust the highlighted selec-
tion.
6. Press the MENU|SELECT button to confirm the change and
proceed to the next selection.
7. After pressing the MENU|SELECT button to set the minutes,
the display will return to the Reading screen.
Note: Pressing the ON/OFF|BACK button at any point will re-
turn to the Settings Menu without making any change.
Setting Date/Time

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Maintenance
Display and Sensor Separation:
1. Remove the probe rods from the base.
2. Flip the TDR display over.
3. Remove the 4 screws on the base using a Philips screwdriver.
4. Gently separate the display module from the base plate. Note:
The sensor cable connected in the center has limited cable length.
Battery Replacement:
1. Follow the steps above to access the batteries.
2. Install four new AA batteries observing correct polarity by
referencing the (+) positive and (-) negative labels.
3. Follow the display installation steps below to reinstall the
display.
Display Installation:
1. Re-connect the sensor cable to the 3.5mm connector on the
back of the display module if previously removed.
2. Insert the foam spacer back behind the sensor cable. The split
end fits around the sensor cable molding.
3. Guide the excess cable back down through the base plate.
4. Align the arrows on the base and display in the same direction.
The USB port should face the same side as the serial number
label.
5.Tighten the four mounting screws.

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Downloading Data Logs to a USB Flash Drive
1. Connect the flash drive directly to the meter’s USB port. Note: A USB ca-
ble is not required or recommended.
2. Press the MENU|SELECT button to open the Settings Menu.
3. Press the READ|Down arrow button to reach the Save to USB option.
4. Press the MENU|SELECT button to select the option.
The data will be saved as a comma-separated text file (.csv) with the serial
number as the filename. These files can be opened with common text-editing
or spreadsheet software. If a previous data file exists on the flash drive with the
same filename, it will be over-written. Be sure to save any existing data logs on
the flash drive prior to saving a new file.
Erasing the internal Data log
1. Press the MENU|SELECT button to open the Settings Menu.
2. Press the READ|Down arrow button to reach the Clear Logs option
3. Press the MENU|SELECT button to select the option.
4. Press MENU|SELECT button again to start the process or the ON/
OFF|BACK button to return back to the menu.
Data Collected
The following information is logged with each reading:
Time, VWC%, Period, Rod Type, Soil Type, VWC Mode
Time: based on the GMT offset selected in the Timezone option (p. 11)
VWC%: Volumetric Water Content based on the Moisture Type setting—
EC Compensated or “TDR 300” (without EC compensation)
Period: Raw Period result (after any applied user calibration)
Rod Type: character is depicted as L: Long (8"), M: Med (4.8"), S: Short
(3"), and T: Turf (1.5")
Soil Type: character depicted as S: Standard, H: Hi-Clay, and D: sand.
VWC Mode: depicted as V for EC compensated or 3 for non-compensated
(TDR-300).
Data Logs

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VWC Measurements
Volumetric Water Content (VWC)
The ratio of the volume of water in a given volume of soil to the
total soil volume expressed as a decimal or a percentage. Three soil
moisture levels of most importance can be defined as follows:
Saturation: All soil pores are filled with water. The VWC will equal
the percent pore space of the soil.
Field Capacity: The condition that exists after a saturated soil is
allowed to drain to a point where the pull of gravity is no longer able
to remove any additional water.
Permanent Wilting Point: The highest moisture content at which a
plant can no longer extract water from the soil.
Additionally, we can define Plant Available Water as the amount of
water between Permanent Wilting Point and Field Capacity. One
rule of thumb is that irrigation should be initiated when half the
Plant Available Water has been depleted.
Time Domain Reflectometry (TDR)
The speed of an electromagnetic wave along a waveguide in soil is
dependent on the bulk dielectric permittivity () of the soil matrix.
The fact that water ( = 80) has a much greater dielectric constant
than air ( = 1) or soil solids ( = 3-7) is exploited to determine the
VWC of the soil. The VWC measured by TDR is an average over
the length of the waveguide.
The sampling volume is an elliptical cylinder that extends approxi-
mately 3 cm out from the rods. The high frequency signal infor-
mation is then converted to volumetric water content. High amounts
of clay or high electrical conductivity (EC>2 mS/cm) will attenuate
the high-frequency signal and affect the reading displayed by the
meter. Very high organic matter content will similarly affect the
VWC reading.

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Optional Accessories
There are two optional items that can be used to expand the capabil-
ities of the TDR. Visit www.specmeters.com for more information
and installation instructions.
TDR Spacer (item 6435SP)
− Placed on the end of the sensor block to aide
in identification of how fast and firm the turf
greens are. The spacer has two orientations
allowing it to work for either desired depth.
− Requires 3.8 cm (1.5”) turf rods.
− For use with firmware version 1.02 or higher
− Allows for the measurement of 1.3cm (0.5") or 2.5cm (1.0") soil
depths.
Pilot Hole Maker (item 6430PH)
If the ground is especially hard or compact, you
can use a Pilot Hole maker to make 3” holes to
aid in starting the insertion of the probe rods.

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To improve accuracy, correlate TDR period readings with a soil-
specific sample set.
VWC data can be correlated by measuring the weight of a known
volume of saturated soil as it is gradually dried, by gradually wet-
ting a known volume soil with measured increments of water, or
by using a neutron probe. In most cases, gravimetric sampling is
performed. This procedure is briefly described below.
1. Establish a number of field sites to sample.
2. Wet each site with varying amounts of water.
3. Obtain FieldScout TDR period reading at each sample site.
4. Extract a known volume of soil at each sample site. Ideally, an
undisturbed soil core. Reduce evaporation - store samples in a
sealed plastic container.
5. Weigh the wet soil samples.
6. Dry the samples (105oC for 48 hours) and weigh again.
7. Plot sample measurements against FieldScout TDR readings.
Regression analysis is used to develop a formula to correlate TDR
readings to the sample data.
Volumetric water content calculations:
VWC = 100*(Mwet - Mdry)/(w*Vtot)
Gravimetric water content calculations:
VWC = GWC *(bw)
GWC = 100*(Mwet - Mdry)/Mdry
b = Mdry/Vtot
Where:
Mwet, Mdry = mass (g) of wet and dry soil respectively
Vtot = total soil volume (ml)
w = density of water (1g/ml)
Appendix 1: Soil-Specific
Reading Correlation

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Rod Length Water
8 inches (20 cm) 60 - 65%
4.8 inches (12 cm) 70 - 75%
3 inches (7.5 cm) 75 - 80%
1.5 inches (3.8 cm) 65 - 70%
Note: The meter does not read 100% in water as the reading is run
through soil equations created to be most accurate in the volumetric water
contents typically found in the selected soil type.
Unable to save data or load firmware from USB flash drive:
Confirm the drive is not full. Verify the drive has FAT or FAT32 format.
Firmware should be in the root directory; outside of any folders.
"No Sensor" appears on the display:
The sensor cable may be dirty or unplugged. Clean the cable connection
Check the cable connection to the display. Confirm that the probe block
is securely plugged into the display.
Appendix 2
Troubleshooting
Sensor Function Verification:
Test readings can be taken in three standard environments; air, distilled
water, and sand saturated with distilled water. It is important that any
troubleshooting be done with distilled water instead of municipal well or
tap water. Test readings are made in a container of distilled water or satu-
rated sand. The container should have a diameter of at least 3 inches
(7.5cm) and should be tall enough so the rods can be completely im-
mersed or inserted.
Readings should be taken with the Soil Type set to Standard and the cor-
rect Rod Length selected. The meter should read VWC=0% in air. In sat-
urated sand, it should read between 35% and 45%. The table below shows
the approximate ranges of volumetric water content that are expected for
the different rod lengths in distilled water.

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Appendix 3: Updating
Device Firmware
Firmware updates may be made available to add or improve the
product features. The firmware can be updated using a USB flash
drive. Firmware update files can be found on the Spectrum web-
site.
1. Copy the latest firmware update from your PC onto the root
directory of the flash drive. The file will not be seen by the
meter if it is renamed or stored within a folder on the drive.
2. Power off the meter.
3. Remove the protective cap from the meter’s USB port.
4. Insert the flash drive directly into the meter's USB port. Note:
A USB cable is not required or recommended.
5. While pressing the DELETE|Up arrow button, press and re-
lease the ON/OFF|BACK button. The meter will beep briefly
and the screen should stay blank.
6. Release the buttons. Note: The display screen will remain
blank during the update process. The meter will beep a second
time once the process has completed and then reboot to the
logo screen. The new firmware will now be displayed below
the Spectrum logo.
7. The display will alert the user if further updates are to be
made and show a message when completed.
8. Remove the flash drive and replace the USB cover.

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The FieldScout TDR is fully calibrated at the factory. Further calibration
is not required nor recommended. The meter has internal calibrations for
standard, sand, and high-clay soil types which will work for many soils.
Each meter will have a small difference in how it responds to identical
soil conditions. This can be due to air being introduced while measuring,
bent probes, loose probes, sensor drift or component tolerances. The me-
ter allows for adjustments to the calibration to account for these differ-
ences. Should the user prefer to perform the calibration; the following are
required:
1. A clean glass or plastic container. The container must be at least
10cm (4”) wide and at least 5.08cm (2”) longer than the length of the
TDR rods.
2. A sufficient volume of unused distilled or de-ionized water to fill the
above container. Note: Tap water cannot be substituted.
Procedure:
1. Pour all of the distilled/deionized water into the container. The water
level must be deeper than the rods currently installed. Note: The wa-
ter and container must be free of minerals and salts to calibrate
properly.
2. From the Settings Menu (page 10), set the rod length to the correct
length of the rods currently installed.
3. From the Settings Menu, choose the Calibration option.
4. Press the Select button to initiate the calibration process. Follow the
display messages.
5. While keeping objects and personnel clear from the area; raise the
meter so the rods are in the air. Press the MENU|SELECT button
and wait until the meter indicates it is ready.
6. Immerse the rods completely in the deionized or distilled water till
the sensor base is in contact with the liquid. Keep the sensor base and
rods centered in the container.
7. Press the MENU|SELECT button and wait until the meter indicates
it is ready.
The meter will then show that the calibration is complete for that specific
rod length. If more than one rod size is being used, a calibration opera-
tion must be done for each rod length used.
Appendix 4: Calibration