Level measurement

74

Continuous level measurement in liquids

4. Instrument selection within the measuring principle

Ultrasonics

Required application data • Pressure and temperature • Vapor pressure of the medium (at 20°C/68°F)

Application limits for ultrasonic level measurement in liquids

• • • • • • • Strong temperature fluctuations in the measuring range can affect the accuracy

• Required material compatibility • Nozzle diameter/nozzle height

• Measuring range • Required accuracy • For bypass/stilling well: Internal pipe diameter

Damping caused by process

Surface of liquid

Filling curtain in the detection range

medium

surface

Calm 0dB

None

0dB

Up to 20°C/68°F 0dB

C

Waves

5 to 10dB

Small quantities

5 to 10 dB (FDU9x = 5 dB) 10 to 40 dB (FDU9x = 5 to 20 dB)

Up to 40°C/104°F

5 to 10dB

Strong turbulence

10 to 20dB

Large quantities

Up to 80°C/176°F

10 to 20dB

Foam Ask Endress+Hauser — — For applications, the sum of dampings (dB) and thus the range (m/ft) can be determined in the diagram from the table. — —

Range calculation and sensor selection Prosonic S FDU9x

R[m/ft]

Example (for FDU92): • Very turbulent surface: • Small quantities of filling curtain in the detection range:

25/82

20dB

FDU93

20/65

5dB

FDU92

• Total:

35dB range approx. 15m/49ft from diagram

10/32

FDU91 (F)

3/9.8

FDU90

0

0

20

40

60

80 A[dB]