OCM Application
This application is specific to monitoring the flowrate in one of the four following
categories of primary measuring devices. Refer to the respective drawings at the end
of this section for weir and flume outlines and transducer location.
Single Exponential, these are flumes and weirs that can be characterized by
a single exponential term (P-40 = 1).
i.e.: Q = K H
X
where Q = flow
K = constant
H = head
X = exponent, characteristic to the primary
measuring device (flume or weir)
Examples:
Primary measuring device exponent
Suppressed rectangular, Cipolletti weir, or Venturi flume 1.50
Parshall Flume, or Leopold Lagco 1.55
V-notch weir 2.50
etc.......
NOTE: Refer to manufacturers specifications for the exact exponent.
The exponents listed above are for reference only.
Palmer-Bowlus flumes, specifically those manufactured by Plasti-Fab or
Warminster Fiberglass (P-40 = 2).
H-flumes, excluding HS and HL sizes, as developed by the U.S. Department
of Agriculture, Soil Conservation Service (P-40 = 3).
Other, these are primary measuring devices that do not fit the first three
categories (P-40 = 4).
As most OCM applications are outdoors, the use of a temperature sensor is strongly
recommended for optimum accuracy. If a temperature sensor is not used, the expected
error due to temperature variations will increase from 0.01 to 0.17% per celsius degree
over the operating range (P-3).
Flow readings are calculated by the HydroRanger I as a function of the head under the
transducer, installed upstream from the primary measuring device (P-40). The flows
are then accumulated in the arbitrary volume units chosen per the time units of P-41 in
an 8 digit totalizer. In the event of a loss of echo, the totalizer will continue being
incremented by the flowrate established from the last valid echo. If the fail-safe timer
expires (’LOE’ is displayed) or when in the calibrate mode, the totalizer will stop being
incremented and hold its last updated value.
The totalizer contents are stored in RAM and will be lost in the event of a power failure.
However, after every 1 hour of continuous operation, the totalizer contents are stored in
PL-399 6 – 29
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