33
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 because the soil moisture
calibration equations were created to be most accurate in the volumetric
water contents typically found in mineral soils.
Appendix 2
Checking VWC Readings
There are two tests that can be performed to check if the meter is operat-
ing properly.
Test 1 (No rods)
: Disconnect the rods from the probe block. Select the
Period option for
Moisture Type
(p. 12). With no rods connected, the
meter should read 1930 ± 30 µs.
Test 2 (Rods attached)
: Readings can be taken in three standard environ-
ments; air, distilled water, and playground sand saturated with distilled
water. It is important that any troubleshooting be done with distilled wa-
ter. Readings taken in tap water can differ greatly from the expected re-
sults observed in distilled water. When readings are taken in water and
saturated 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 (p. 11) and
Moisture Type
(p. 12) set to
TDR 300 mode. Be sure that the correct
Rod Length
(p. 11) is selected. The meter should read VWC=0% in air.
In saturated sand, it should read between 35% and 45%. The table below
shows the approximate ranges of volumetric water content that are ex-
pected for the different rod lengths in distilled water.
