HOBO MicroRX Station Manual
1-800-LOGGERS 18
www.onsetcomp.com
•
If the reference point is the bottom of the channel, then
the value is represented as P in the diagram earlier in this
section.
•
If the reference point is above the water level (such as
when using ground level as the reference point in a storm
sewer), then enter a negative number.
•
If the reference point is below the water level, then enter
a positive number.
8.
Click Save.
Water flow will be calculated starting with the next connection
to HOBOlink.
Setting up a Water Flow Channel for a General Flume
If you are using a flume along with the water level sensor, then
HOBOlink can calculate the water flow using a general flow
equation supported by a wide range of flumes that require only
one water level measurement to calculate flow, including ramp,
cutthroat, Parshall as well as broad-crested rectangular weirs.
The equation that HOBOlink uses is: Water Flow (Q) = C *
(Water Level - Head Offset)
n
. Flumes that require require two
or three water level measurements to calculate flow are not
supported.
For this equation to be accurate, there are constraints on the
flow conditions and flume design, including:
•
Minimum and maximum flow rates
•
Minimum and maximum head levels
•
Ratio of the width of the weir/flume to the head
•
Ratio of the height of the weir/flume to the head
•
Location in the flume or weir for measuring the head.
The constraints depend on the type and characteristics of the
flume you are using, which can be obtained from the flume
manufacturer.
Important:
Make sure the station has started logging and you
have configured the water level channel with a reference level
reading before performing these steps.
To set up a water flow channel using a general flume:
1.
Click Devices and then RX Devices, and find the station you
want to configure. Click the arrow next to the
icon and
select Module/Sensor Configuration.
2.
Under the water level module in the Configuration menu,
select Water Flow.
3.
Click the checkbox to Enable Channel.
4.
Click the checkbox to Enable Graph and type a label
(optional).
5.
For the Measurement Method, select General Flume.
6.
For the Flume Coefficient, enter the C value listed in your
flume’s equation table, which can typically be found in the
flume manufacturer’s documentation. The Flume
Coefficient may also be labeled K by some manufacturers so
be sure to check how the coefficient is being used in their
equation to make sure it is the right one to enter here.
7.
For the Head Offset, enter the value in either meters or
feet, using the same units as you entered the reference
water level in the water level channel. An example of Head
Offset is shown in the following diagram of a ramp flume.
•
If you are using a ramp flume as shown in the diagram
below and the top of the ramp is the reference point,
then enter 0.
•
If you are using a ramp flume and the bottom of the
channel leading to the ramp (or crest) is the reference
point, then enter the height of the ramp or crest for the
Head Offset (represented as P in the diagram).
For other types of flumes, such as this example diagram
where the water level (or H) is being measured from the
bottom of the flume:
•
If the bottom of the flume is the reference point for both
the water level and head, then enter 0 for the head
offset.
•
If the reference point is above the water level (such as
when using ground level as the reference point in a
storm sewer), then enter a negative number.
•
If the reference point is below the water level, then enter
a positive number.
8.
For the Head Exponent, enter the n value listed in your
flume’s equation table, which can typically by found in the
flume manufacturer’s documentation.
9.
Click Save.
Water flow will be calculated starting with the next connection
to HOBOlink.
Setting up a Water Flow Channel for a Stage-Discharge
Table
You can set up a water flow channel that is calculated based on
up to 20 stage-discharge points that you enter. Keep in mind
that the units of the stage-discharge table for water flow are
assumed to be the same as those entered for the reference
water level. If the reference water level was entered in meters,
then points in the table must be entered in meters and l/s
(liters per second). If the reference water level was entered in
feet, then points in the table must be entered in feet and cfs
(cubic feet per second).
Before you begin setting up the channel, you will need to
determine the values to enter into the stage-discharge table.
HOBOlink does not derive a stage discharge curve. Use another
method to determine the stage-discharge curve for your site
and then enter points from that curve into the HOBOlink stage-
discharge table. HOBOlink linearly interpolates between the
points that you enter. You can estimate and enter intermediate
