Mode Of Operation; Measuring Principle - Siemens SITRANS DA400 Operating Instructions Manual

Description

3.4 Mode of operation

3.4 Mode of operation
3.4.1

Measuring principle

Mode of operation
Leaks in the valves of oscillating positive displacement pumps are flows in which cavitation
occurs. This generates sound waves. The sound waves are transferred to the valve housing.
The acoustic emission sensor of the acoustic diagnostics unit detects these sound waves on
the exterior of the valve housing.
The sound pressure level L generated by the leak depends on the hydraulic power P
follows:
L
L
η
P
hyd
P
0
The hydraulic power at a valve depends on the pressure differential Δp and the flow rate Q
as follows:
P
hyd
P
hyd
Δp
Q
The valves of an oscillating displacement pump open and close periodically. The sound
pressure level of an intact valve is low. The sound pressure level of a defective valve
depends on the valve position. A pump working normally changes the valve position
periodically between open and closed. The sound pressure level therefore fluctuates
periodically. The appearance of a sensor signal and sound pressure level on an intact valve
and a defective valve, is shown in the following two figures.
14
η P
hyd
P
Sound pressure level
Energy conversion coefficient, from hydraulic to acoustic
Hydraulic power
Reference power
p Q
Hydraulic power
Pressure differential
Flow rate
SITRANS DA400 for oscillating positive displacement pumps with protection against explosion
Operating Instructions, 10/2007, A5E00841127-01
as
hyd