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Measurement technique and data acquisition
4.4 Measurement technique and data acquisition
4.4.1 Overview
Fig. 4.16 gives a scheme of the automatic measurement devices. The whole data acquisition
device 1 had to be programmed to suit the needs of the present research study (Appendix 2.2). The
central command unit controls the following devices:
• The frame command unit, moved the probe support to the desired positions and allowed a
semi-automatic data acquisition 2 (§ 4.4.2).
• The leveling unit performed the acquisition of the water and bed levels in the channel
(§ 4.4.3).
• The velocity measurement unit - an ultrasonic velocity profiler, based on the Doppler effect
- acquired the velocity profiles over the whole channel depth along 3 axis (giving the 3D
velocity distribution) with an acquisition frequency of about 80 Hz (§ 4.4.4).
• These automatic measurements were completed with manual recordings of the sediment
transport rate and the water levels and bed topography along the outer side wall (§ 4.4.6).
Central Command Unit
Velocity Acquisition Unit
TCP/IP
General
command
file
Command files
Command files
Level Acquisition Unit
Multiplexer
Frame Command
Unit
10 V
Supply Unit
Meas. frame
US Probes
UVP
Probe
10 V
220 V
xyz
Channel
Figure 4.16: Scheme of the data acquisition
1. Including the Central Command Program and the Chef Program
2. The acquisition frame (traversing system 2 x 2 m) was moved manually to 8 predefined positions
(every 15°). At each position, the frame automatically acquired the data within the frame area on a
9 x 9 cm grid (about 1500 automatic measurement points over the whole channel).
EPFL Ph.D thesis 2632 - Daniel S. Hersberger November 9, 2002 / page 83