Xylem H-340 - Manual (Page 9)

H-340
H-340 User Manual 1-3
1. Empty the graduated cylinder.
2. Start the water flow into the funnel.
3. Wait until at least 100 bucket tips have occurred (1% resolution).
4. Stop the water flow.
5. Observe and record the water volume in the graduated cylinder.
6. Use the formula below to compute the actual rainfall in the graduated cylinder..
7. Calculate the rainfall measured by the rain gauge (0.01inches x number of tips).
8. Compare the difference between these two values.
9. Adjust the counterweight as needed and repeat until the two values are identical or within an
acceptable difference.
The rainfall “volume” equation below converts the volume in the graduated cylinder (mL) into
the equivalent rainfall (in inches) captured by an 8 inch diameter funnel.
RAINFALL
NmL
L
mL
in
L
in
NmL x
inches inches
=
Ч Ч
= Ч −
1000
61025
4 0
121405 10
3
2
3
.
( . )
.
π
1.5 Adjusting the Tipping Bucket Mechanism
Warning: DO NOT ADJUST THE BUCKET STOPS.
Adjusting the stop posts causes a false reading of equal amounts of water in each bucket. This is
due to the variation of distance the bucket center must travel after passing the bottom of the
funnel. Do not adjust the bucket stops in an attempt to balance the weight of the buckets. Instead,
the H-340 provides an adjustable screw parallel to the buckets by which the bucket weight
balance can be accomplished. This eliminates the need to adjust the stops and compensates for
any inequality of weight due to manufacture and assembly, and gives equal travel to each bucket
as the center passes the flow of water.
The counter weight underneath the bucket mechanism can be adjusted (up or down,) to set the
bucket volume (# tips/unit rainfall). See Figure 2. The up/down counter weight adjust
instructions in steps 1 and 2 may seem to be intuitively backwards however, realize the center of
gravity of the bucket and counterweight is above the pivot.