NT216C GB1
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1-1 Measurement principle:
Calculation of the sound velocity in the product
The equipment is connected to a single probe being perpendicular to a pipe generating
line.
At a rate set by the user, the probe sends a pulse which is reflected by the opposite pipe
inner wall. Based on the knowledge of:
- The measured time (t) between the emitting pulse and the receipt of its echo,
- The pipe inner diameter D (resulting from the outside diameter and the pipe thickness)
- The dead time (pulse transit time in the probe face and through the pipe wall),
the equipment determines the sound velocity inside the product under the actual conditions
of pressure and temperature.
More precisely, time t between emission and receipt is equal to :
t = 2 x (time in probe) + 2 x (time in wall) + 2 x (time in product)
That is to say:
t =
2
0
2
2
t
e
Cm
D
Cp
With : D : inside diameter of the pipe / e : pipe thickness / Cm : sound velocity inside pipe
material / Cp : sound velocity inside the product .
If time
2
2
0
t
e
Cm
is the dead time, the sound speed in the product is equal to:
Cp
C
D
t
t
dead
2
Remarks: In the event of a new and smooth pipe, numerous reflection phenomena intended
to disappear with time can be observed
.
These numerous echo phenomena can make necessary to reduce the measurement rate of
the MiniSonic ISD or PSD so that the echo phenomena generated by the preceding
transmission can be completely absorbed before a new transmission.
