Endress+Hauser FMU 40 - Page 4

Prosonic M
Endress+Hauser
4
Input
Measured variable
The distance D between the sensor membrane and the product surface is measured
(page 2). Using the linearization function, the device uses D to calculate:
• Level L in any units
• Volume V in any units
• Flow Q across measuring weirs or open channels in any units
The measuring range is limited by the range of a sensor. The sensor range is, in turn,
dependent on operating conditions. The diagram below defines the effect that echo
attenuation has on the sensor’s measuring range. The ideal echo attenuation curves
for each sensor are shown in the diagram. A number of echo attenuation sources that
affect proper sensor selection are shown in the table.
1. Determine which of the influences shown are appropriate for your process.
2. Add the corresponding attenuation values.
3. From the total attenuation, use the diagram to calculate the sensor range.
Measuring range
Operating frequency
Sensor FMU 40 FMU 41 FMU 43
Frequency approx. 70 kHz approx. 50 kHz approx. 35 kHz
Pulse frequency
• 2-wire devices, maximum 0.5 Hz
• 4-wire devices, maximum 2 Hz
The exact values are dependent on the type of device and supply voltage.
FMU 40
FMU 41
FMU 43
10 20 30 40 50 60 70 80
3
10
16
23
26
30
36
43
Temperature difference between
sensor and surface
Example (for FMU 43)
Approximate range = 15.5 ft.
Dust-covered rubble
Medium dust development
Not in filling curtain
Temperature differential < 68°F
Approximate dB
50
10
0
0
60 dB
50
Fluid surface
Calm
Waves
Strong turbulence (agitators, etc.)
Foaming
Bulk material surface
Hard, rough (e.g. rubble)
Soft (e.g. peat, dust-covered clinker)
Filling curtain in detection range
None
Smalll quantities
Large quantities
To 68°F (20°C)
To 104°F (40°C)
To 176°F (80°C)
Dust
No dust formation
Little dust formation
Heavy dust formation
Attenuation
0 dB
5 to 10 dB
10 to 20 dB
Consult factory
Attenuation
40 dB
40 to 60 dB
Attenuation
0 dB
5 dB
5 to 20 dB
Attenuation
0 dB
5 to 10 dB
10 to 40 dB
Attenuation
0 dB
5 to 10 dB
10 to 20 dB
15.5
Attenuation / dB
range in feet