A. Amplitude (mV)
B. Distance
C. Surface Threshold
D. Surface echo
E. Disturbance
F. At least 500 mV margin
Contact your local Emerson
™
representative if the transmitter is still having difficulties to
track the product surface after applying the guidelines.
Guidelines for setting the interface threshold
• The Interface Threshold should be approximately 50% of the interface signal
amplitude.
• If possible, Interface Threshold should be higher than Surface Threshold.
Typical surface echo amplitudes and thresholds
Figure 7-13 to Figure 7-15 shows typical signal amplitude of the surface echo (signal
strength) at different distances to the surface. The signal amplitude of the surface echo
depends on the dielectric constant of the product. Product with a high dielectric constant
(for example water) gives better reflection (a strong signal amplitude) than product with a
low dielectric constant (for example oil).
Note
The amplitude of the surface echo is also depended on the distance to the product
surface. Since the signal is attenuated along the probe, the surface echo will be strongest
close to the tank top, and then weaker further away from the tank top. In addition, the
signal amplitude of the surface echo can vary because of product, foam, turbulence,
ambient temperature and so on.
The values in Figure 7-13 to Figure 7-15 are estimations. Significantly different Surface
Threshold values may have to be used to handle special tank conditions and applications.
Reference Manual Service and troubleshooting
00809-0100-4530 April 2019
Reference Manual 203
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