Thermo Scientific HB-S2000, Руководство пользователя

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Sarasota 2000 Ultrasonic Multipath
Flowmeter
Section 2, SYSTEM COMPONENTS, Page 2-15 Thermo Fisher Scientific
SYSTEM COMPONENTS
2.4 Ultrasonic
transducers
Each velocity path requires two transducers and each ultrasonic depth requires one.
The transducers are available in a number of frequencies. See Section 1.2.6 for frequency
selection. The frequency of the ultrasonic depth transducer, if used, is not normally critical.
1 MHz is usually used if the velocity transducer frequency is 1 MHz or 500 kHz otherwise.
The diameter of the transducer is different for different frequencies. This is to maintain the
angular spread of the beam which is a function of frequency and diameter.
The transducers for the Sarasota 2000 are “smart”, with local circuits for the drive voltage
(HT) generation and the receiver amplifier built in to minimise losses and optimise signal-to-
noise ratio. In the case of the 1 MHz transducers the size of the transducer is limited and the
local circuit is separated from the transducer in a potted in-line housing called a “Tbox”,
Transducers may be wired individually to the flowmeter (rear panel connections A to H for
velocity and W to Z for depths) or, using the multi-drop method, via “star” junction boxes in
each transducer array. In the latter case up to 4 transducers may be joined to each rear panel
connector. A mixture of multi-drop and direct connections may be used. For example, if there
are 5 transducers in an array, 4 may be wired via a star box and the fifth wired directly.
The maximum capacity with direct connections is 8 paths and 4 ultrasonic depths.
The maximum capacity with multi-drop is 32 paths and 16 depths.
The transducers have programmable addresses. Addresses 1 to 4 are normally used. When
using multi-drop, the transducers connected to each star box must be pre-programmed with
different addresses to enable each one to be operated separately by the flowmeter. Specialist
equipment is necessary to programme the transducers and it is usual to supply them with
specified addresses.
2.4.1 1 MHz transducers
For use with path lengths up to 10 metres. In cases where serious attenuation is anticipated
(for example, sewage) it is recommended that the use be restricted to 5 metres and a lower
frequency be used above that. Of course the lower frequency requires a greater depth of
water in which to operate and this must be taken into account (see Section 1).
An in-line Tbox is fitted in line with each transducer.
The co-axial cable from the T box must be connected to a star box or extended to run directly
to the flowmeter. Coaxial cables to the flowmeter enclosure are usually made up on site.
Cables may be supplied to length with made up ends if specified with the order but this often
makes the installation more difficult where there is the need to pull cables through ducts.
2.4.2 500 kHz Transducers
For use with path lengths above 10 metres. In cases where serious attenuation is anticipated
(for example, sewage) it is recommended that 500 kHz transducer be used above 5 metres.
At the upper end, they may normally be used up to 80 metres. For cases where serious
attenuation is anticipated, lower frequency transducers should be used for paths above 50
metres.