Valeport BFM001, Руководство по эксплуатации, Страница: 4 / 32

Model 001 & 002 Flowmeter Operating Manual
MANUAL-1550859975-1 | issue: 1.1
©
2021
– Valeport Ltd
Page | 1
1 Design & Configuration
The Valeport "Braystoke f
lowmeter” (BFM) 001 and BFM002 flowmeters have been designed to
withstand long periods of operation underwater and to need little maintenance with as few moving
parts as possible. They are designed to accurately measure water velocity in open channels with
flows varying from 0.03 m/s to 10 m/s (BFM001), or 0.05m/s to 5m/s (BFM002). The calibration of
the meters is based upon Group Calibrations carried out by HR Wallingford to standards
established by the British Standards Institution.
The flowmeters are available with both Wading and Suspension Sets to allow the equipment to be
employed in a wide variety of applications.
1.1 Basic Design
Refer to Figure 1 (BFM001) and Figure 3 (BFM002) .
The basic principle of the Meter is to open and close a reed switch by rotating magnets around it,
to open and close a circuit producing a pulse. The pulse count is displayed on one of the liquid
crystal displays in the Control Unit. A bias magnet fitted into the meter hub produces a strong
magnetic field and allows only one pulse per impeller revolution. The only moving part of the Meter
is the neutrally buoyant impeller, which houses the magnets. The bearings fitted to this impeller are
made from PTFE plastic and are water lubricated. Since the impeller has very little weight in water,
the load on the bearings is negligible. The impeller and hub incorporate an anti
‑
weed system that
prevents weed entangling around the impeller shaft. Once the chamber around the impeller shaft
and bore have filled with water, very little or no silt will enter the bearings.
1.2 Operational Use
The flowmeter may be used in two different ways according to operational requirements, and
equipment supplied:
A. Wading
‑
where the water depth permits, the operator may use the Meter clamped to the
wading rods, wading across the river or stream and making velocity measurements at the
required intervals and depths. The centimetre markings on the wading rods permit the
Meter to be accurately positioned at the required height in the water column, and also to
establish the total water depth to enable profile depths to be calculated.
B. Suspension
‑
in deeper water the Meter may be suspended from a cable over a bridge or
parapet to make the required velocity measurements.