BM Tecnologie Industriali TTFM100-F18-NG, Instruction Manual

Page: 4 / 110

Mod.BM43
COM
Vers.1.0
16/11/2005
Page 4 of
110
1 WORKING PRINCIPLE
When the ultrasonic wave spreads in a liquid, the flow will cause a changing in the
spreading time depending on downstream or upstream current.
The ultrasonic wave going towards the same directions of the flow increases the spreading
speed, while the ultrasonic wave going towards the opposite side of the flow decreases
the spreading speed.
If the difference between the two spreading times is accurately measured, it would be
possible to calculate the flow speed (see the following picture).
The measures are taken b
y 2 sensors in direct contact with the pipe’s external surface.
The UP sensor ( RED ) is placed on the upper side of the pipe’s external surface, the DOWN
sensor ( BLUE ) is placed on the lower side of the pipe’s external surface.
The sensors positions could l ook like a “Z” or like a “V” or a “W”, if the pipe has a small
diameter (in the previous sketch, the sensors are “Z” mounted).
The sensors are alternatively used to receive the ultrasonic pulses sent through the way
pipe - fluid - pipe.
The difference between the transmitted and received signals upstream and downstream is
calculated as follows:
(1)
(2) (3)
 +


=
VSIN Co
COS
D M
Tup
 −


=
VSIN Co
COS
D M
Tdown
Tdown Tup
T
SIN
D M
V
*
*
2
*


=