Spectrum Technologies Field Scout TDR 350 User manual

TDR 350
Soil Moisture Meter
PRODUCT MANUAL
Item # 6435

2
CONTENTS
Shaft Dimensions 4
Specifications 5
Batteries 6
Button Functions 8
Display Screens 10
Meter Calibration 14
Updating Firmware 15
Electrical Conductivity 16
Meter Operation 18
Replacing or Re-attaching the Probe Block 21
Replacing the Display 22
Field Scout Mobile App/SpecConnect 23
Pairing TDR350 with FieldScout Mobile App 25
Data Logs 27
VWC Measurements 29
GPS Status 30
Optional Accessories 31
Appendix 1: Checking VWC Readings 32
Appendix 2: Soil-Specific Calibration 33
Appendix 3: FAQ 35
This manual will familiarize you with the features and operation of
your new Field ScoutTM TDR 350 Soil Moisture Meter. Please read
this manual thoroughly before using your instrument.

3
Thank you for purchasing the Field ScoutTM TDR 350
soil moisture, electrical conductivity and soil surface
temperature 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. The meter also
measures soil surface temperature. The user can quickly
transition between taking VWC readings in standard
and high-clay mode.
The TDR 350's shaft-mounted probe allows the user to
take measurements while standing. The meter’s built-in
data logger can record data from several sites and elimi-
nates the need to record data manually. The data points
can be viewed with the FieldScout Mobile app that
maps out soil measurements using logged GPS loca-
tions. Measurements can also be saved to a USB drive
that is plugged into the built-in USB port.
Contents
Your shipment includes the following components:
- TDR 350 meter (in collapsed position)
- Carrying case
- 4 AA batteries
Note: TDR rods are sold separately
General overview

4
Shaft dimensions
The following are the dimensions of a fully extended
shaft. It is possible to reduce the length of the meter to
23” (58.5 cm) by adjusting the lower half of the shaft.
38"
19.5"
2.4"
14"
5"

5
Measurement
Units
Percent volumetric water content (VWC)
Period (raw sensor reading)
Resolution VWC: 0.1% VWC units
EC: 0.01 mS/cm
Temperature: 0.2 ˚F (0.1 ˚C)
Accuracy VWC: ±3.0% volumetric water content
with electrical conductivity < 2 mS/cm
EC: ± 0.1 mS/cm
Temperature: ± 1.8 ˚F (± 1 ˚C)
Range VWC: 0% to saturation (Saturation is typi-
cally around 50% volumetric water)
EC: 0 to 5 mS/cm
Temperature: -22 to 140 ˚F (-30 to 60 ˚C)
Power 4 AA batteries
Lithium batteries will optimize battery life
Logger
Capacity
50,000 measurements
Display Backlit, high-contrast, graphic LCD
GPS Accuracy < 2.5m
Weight 4.3 lbs. (1.9 kg)
Probe Head
Dimensions
2.4” x 1.4”
(6cm x 3.5cm)
Shaft
Dimensions
Extended Length: 38” (96.5cm)
Collapsed Length: 23” (58.4cm)
Width: 1.4” (3.5cm)
Available
Rod
Dimensions
Turf 1.5” (3.8cm)
Short 3” (7.6cm)
Medium 4.7” (12cm)
Long 7.9” (20cm)
Diameter: 0.2” (0.5cm)
Spacing: 1.2” (3cm)
Specifications

6
Changing the batteries
The TDR 350 requires 4 AA batteries. The battery holder
is on the underside of the display unit. The sensor is at-
tached to the display via a cable that is plugged into a
socket between the battery holders. The cable can be
pulled out of and pushed back into the shaft through a
grommet at the top of the shaft.
Do not permanently remove the foam plug. It ensures
the plug does not come detached.
STEPS:
1. Collapse the shaft.
2. Turn the TDR 350 upside down and remove the 4
screws. Open the bottom and separate the display
module from the base plate. This may require pulling
the cable slightly out of the shaft.
3. Install batteries and ensure correct polarity by refer-
encing the (+) positive and (-) negative labels at either
end of each slot.
4. Plug the cable connector back into the larger stereo
jack.
5. Mount the display box back onto the base plate. As
you do this, make sure the side with the USB port is
on the same side as the label.
6. Re-attach the 4 screws.
Batteries
plug
grommet
cable

7
Battery life
The battery level is checked every time the display
unit is turned on. If the battery level is low, or if a
battery is inserted incorrectly, this low battery im-
age shows on the full screen for about 10 seconds
and then the display will automatically turn off.
In addition to frequency of use, battery life is im-
pacted by use of the backlight and GPS receiver. If
not needed, the GPS feature should be disabled.
The backlight can be set to AUTO mode (p. 12).
This allows enough time to see the reading without
unduly taxing the battery. The chart below gives a
rough estimate of the number of readings that can
be taken given certain configuration parameters.
Total Readings
Bluetooth GPS Backlight Alkaline Lithium
ON ON ON 12,000 24,000
ON ON OFF 24,000 35,000
OFF OFF OFF 150,000 225,000

8
Button Functions
Basic Button Operations
ON/OFF or BACK button
Press this button briefly to turn on the
display. The meter will then display
the Data screen (p. 11). To turn the
meter off, press and hold this button
for about 2 seconds.
When in the Settings Menu screen (p. 12), press
this button to return to the Data screen. If you are
in a settings option that requires its own screen,
this button will return you to the Settings Menu
screen
MENU or SELECT button
When in the Data screen, press this but-
ton to go to the Settings Menu screen
(p. 12). When in the Settings Menu
screen and on a menu option, press this
button to browse through the different
choices for that specific menu selection.
In some cases, selecting a settings option will take
you to another screen for further action.

9
DELETE or UP button
When on the Data screen (p. 11), press
this button to delete the last measured
data point from the computed Average
and decrement the Count.
When on the Settings Menu screen (p. 12), press
this button to scroll up to the previous menu item.
READ or DOWN button
When on the Data screen, press and
release this button to take a sensor
reading. Press and hold to clear the av-
erage and reset the sample count to 0.
When on the Settings Menu screen, press this but-
ton to scroll down to the next menu item.

10
Display Screens
The TDR 350 has 3 main display screens;
- Startup Information screen
- Data screen
- Settings Menu screen
Startup Information screen
The Startup Information screen is displayed for
about 2 seconds after the display is turned on.
If desired, the startup screen can be kept on for a
longer duration. While powering up the meter,
press and hold the On/Off/Back button to contin-
ue displaying the Startup Device Information
screen. Release the button to proceed to the Data
screen.

11
Data screen
Readings from
the sensor are
displayed on the
Data screen. The
battery level in-
dicator appears
in the upper right
corner. The run-
ning average and
number of readings included in that average are
shown in the lower right corner. Pressing and
holding the READ button will clear the average
and re-set the counter to 0.
When disabled, the GPS and/or
Bluetooth icons will no longer
be visible. When visible, the
GPS icon will indicate the quali-
ty of the GPS fix (p. 29).
When the Bluetooth is enabled
but the TDR is not connected to
a mobile device, the Bluetooth
icon has a bar through it (see
image in data screen at top of
page). When the TDR is con-
nected to a mobile device, the bar is removed (see
image to the right).

12
Settings Menu screen
The contents of the Settings Menu are shown on the
following figure. Use the arrow buttons to scroll to the
desired option. The options are described below. For
most options, pressing the Select button simply tog-
gles you through the different choices for that option.
Some options require an additional step or steps.
Clear Average*:
Clears the current average
and resets the counter to
zero.
Rod Length: Select the
size rods attached to me-
ter. See p. 5 for options.
Soil Type: Choose Stand-
ard, Hi-Clay or Sand.
Clear Logs*: Initiates
erasing of data from inter-
nal memory.
Save to USB*: Initiates
transfer of data to USB
flash drive.
Backlight: The three options are ON, OFF, and AU-
TO. In AUTO mode, the backlight will be illuminated
for 5 seconds after a measurement is taken and then
shut off.
GPS, Bluetooth, Sound: Enable or disable these op-
tions. If location is not needed or a mobile devices is
not used, disabling these features will improve battery
life.

13
Temp Source: Choose Soil Sensor or IR Sensor.
Temp Units: Choose Fahrenheit or Celsius.
Moisture Type: Choose volumetric water content
(VWC%), raw sensor reading (Period), or TDR 300
mode. The latter will report a VWC that matches the out-
put of the TDR 300 meter (no EC optimization).
EC Units: Choose simple EC value (mS/cm) or the Sa-
linity Index (see p. 17).
Auto-Off: Choose how long the meter will stay on before
automatically powering off.
Current Date, Current Time: These are reported val-
ues. They cannot be manually adjusted. This information
is acquired from the GPS signal.
Timezone: Choose the offset from Greenwich Mean
Time. As you change the offset, the Current Time and
Date will be updated.
Daylight Savings: Options are ON or OFF.
Calibration*: Initiates calibration sequence (see p. 14).
Factory Defaults*: Returns all meter settings to the fac-
tory default values. See p. 34.
* Pressing Select button for these options brings up an
additional screen.

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The meter has internal calibrations for standard,
sand, and high-clay soil types. It also has the op-
tion of outputting a value that matches its prede-
cessor, the TDR 300. These calibrations will work
for a large number of soils. However, each meter
will have a small difference in how it responds to
identical soil conditions. This is due to sensor drift
or variability in the electronic components used
during manufacturing. The meter allows for adjust-
ments to the calibration to account for these differ-
ences. Therefore, if two meters are giving slightly
different readings in the same soil, the output of
the meters can be standardized such that the meters
can be used interchangeably. After calibration, a
TDR 350 in "TDR 300" mode (see p. 13) should
read the same as a TDR 300 meter.
To perform the calibration, you will need a 6" di-
ameter plastic container of distilled or de-ionized
water. The container must be at least as tall as the
length of the TDR rods. The procedure is as fol-
lows:
1. From the Settings Menu (p. 12), scroll to the
Calibration option. Press the Select button to
initiate the calibration process.
2. Hold the meter so the rods are in the air. Press
the Menu/Select button and wait until the me-
ter indicates it is ready.
3. Immerse the rods completely in the water.
Press the Menu/Select button and wait until
the meter indicates it is ready.
Meter Calibration

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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 operation
must be done for each one.
Note: This procedure is different than a soil-
specific calibration (Appendix 2, p. 32) where a
unique calibration curve is generated.
Updating Firmware
The firmware of the TDR 350 can be updated us-
ing a USB flash drive. Firmware update files can
be found at the Spectrum website.
1. Copy the latest firmware update from your PC
onto your flash drive.
2. Power off the meter.
3. Insert the flash drive into the meter's USB port.
4. While holding down the Delete button, press
the On/Off/Back button. The meter will beep.
5. Release the Delete button after the meter beeps
a second time.
6. Remove the flash drive.
The meter will then power up as usual.

16
Electrical Conductivity
Electrical Conductivity
Knowledge of the salinity level of your soil is an im-
portant component of irrigation and nutrient management.
The source of the salts in the soil ranges from the original
parent material to additions from natural sources and man-
agement activity. Often, having salt in the soil has a nega-
tive connotation. This is because when the soil solution
has a high salt concentration, plant roots cannot bring in
sufficient soil moisture. However, fertilizer exists as salt
ions in that same soil solution. So, if the salt level is too
low, the plant cannot get the nutrients it needs.
Direct measurement of salt content can only be done by
subjecting a field sample to laboratory analysis. Fortunate-
ly, the electrical conductivity (EC) is a function of the dis-
solved salts in the soil. EC is expressed in units of mS/cm.
This proxy measurement is possible because, as salts dis-
solve into the soil, they disassociate into ions which con-
duct electricity.
The EC measured by an electrode is defined as the bulk
EC. The significance of this value depends on how the
sample was prepared. The EC reported by a soil lab is typ-
ically the saturated media extract. Briefly, distilled water
is added the soil until it glistens. The soil solution is given
time to equilibrate with ions on the soil exchange sites.
This soil water is then suctioned off to be measured.
Measuring the EC of diluted soil/water solutions (such as
1 part soil: 2 parts water) is also common. The determina-
tion of whether the EC is within an acceptable range is
based on the type of sample being measured.
The TDR 350 uses the same metal rods used for soil mois-
ture sensor as the electrodes for the EC circuit. The value
measured is an average for the entire depth sampled.

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Salinity Index
The TDR 350 measures the bulk EC of soil that may or
may not be saturated. There are two competing mecha-
nisms at place. As the soil dries, the remaining solution in
the pore space becomes more concentrated which increas-
es its EC. However, reduced water in the pores leads to a
longer and more tortuous path between the sensor elec-
trodes, which decreases EC. The second mechanism dom-
inates. This means that bulk EC will decrease as soil
moisture decreases. EC measurements at different sam-
pling times are comparable when the moisture content for
each measurement is the same. This is easily accom-
plished if readings are always taken when the site is at
field capacity. Field capacity is defined as the condition
that exists when a saturated soil is allowed to drain to the
point where the pull of gravity can no longer remove any
additional water.
The TDR 350 also gives the option to report EC in the
form of the Salinity Index. The salinity index is defined as
the ratio of the bulk EC to the volumetric water content
(expressed as a decimal). For example, if the bulk EC is
0.25 mS/cm and the VWC is 22%, the Salinity Index
would be reported as 1.14 (0.25 ÷ 0.22 = 1.14). Therefore,
the Salinity Index combines VWC and EC (corrected for
temperature) into a parameter that will be less dependent
on the sub-saturated water content.

18
Meter Operation
Setting up the meter
The telescoping shaft (fig. 1) can be used in an extended
or retracted position. To adjust the length, remove the fas-
tening bolt and push or pull the shaft into its new posi-
tion.
Screw the rods into the sockets at the bottom of the probe
block.
Configuring the meter
Meter configuration is done in the Settings Menu (pp. 12
- 13).
The TDR 350 can be set to one of three Soil Type modes,
Standard, High Clay, or Sand. The Standard mode will be
appropriate for most mineral soils. The High Clay mode
will be more accurate for soils with higher clay contents
(> 27%). Sand is applicable for sand based sports fields or
golf greens. There are 3 Moisture Type options. VWC%
mode displays the moisture content optimized by the out-
put of the EC sensor. Period mode displays the raw sensor
reading. This mode is intended primarily for trouble-
shooting or for soil-specific calibrations. TDR 300 mode
displays a reading that will match the output of a TDR
300 meter.
Figure 1. Shaft, fastening bolt, and rods

19
To geo-reference data, enable the GPS capability. If you
are using the FieldScout Mobile app (p. 22), Bluetooth
functionality must be enabled. When Bluetooth is activat-
ed, it will always be on while meter is powered up. If
GPS is disabled, the app will use the phone's GPS in-
stead.
Display
Figure 2 shows a sample
data screen. The GPS,
Bluetooth, and battery
status are shown in the
upper right corner. Soil
moisture, EC, and temper-
ature data are displayed in
the top half of the display.
The average reading and number of readings included in
the average are visible in the lower right corner. The cur-
rent Rod Length and Soil Type are shown in the lower
left corner.
Taking Readings
Push the rods into the soil. When taking a measurement,
it is important that the rods be fully inserted into the soil.
If not, part of the sampling volume will be composed of
air and the reading will be inaccurately low. For the same
reason, the probe should be inserted with a steady, down-
ward pressure. If the rods are wiggled into the soil, air
pockets can be created adjacent to the rods that will result
in low readings. The probe should not be struck with a
hammer or other blunt instrument as this can cause dam-
age to the internal electronics. Also, care should be taken
to ensure the rods are inserted as parallel to one another
as possible. This will not have a large affect on the read-
ing but will decrease the chances the rods will be bent or
broken. Likewise, it is best to avoid areas with rocks or
Figure 2.Sample data screen

20
other material that can cause the rods to deflect or bend.
If the ground is especially hard or compact, you can use a
Pilot Hole maker (item 6430PH) to make 3” holes to aid
in starting the insertion of the probe rods.
Press the READ button to initiate the measurement se-
quence. The reading should appear almost instantaneous-
ly. If the display does not detect the sensor, it will display
dashes. Check that the sensor is securely attached (see p.
21).
Note: The TDR rods are manufactured from type 303
stainless steel and are designed to bend if non-vertical
force is applied to them. This serves to protect the TDR
block electronics from potential damage that could be
caused by excessive force.
Occasional rod bending is normal, and can be expected
during the course of sampling. Longer rods will be more
susceptible to bending than shorter rods. If bending oc-
curs, rods should simply be bent back to parallel position,
perpendicular to the TDR block. Measurements will con-
tinue to be accurate provided that rods are reasonably
close to parallel.
If care is not taken to reposition rods to a parallel posi-
tion, subsequent pressure on the rods will accentuate the
bending and may cause the rods to break.
Rods should be considered maintenance items that may
need to be replaced over time, depending upon the nature
and frequency of sampling. The rods will wear most rap-
idly in sand-based root zones.