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Fig. 10 Echo Pattern under Strong Interference
The left figure above is the echo pattern under strong interference and the figure
shows high interference waves from left to right. Under the condition, ground con-
nection can not solve all problems. At this time, we should judge the interference is
from the power supply or the air.
If the electromagnetic interference is from air, a metal instrument box should be
made for the instrument and the instrument box should be grounded.
Therefore, if the electromagnetic interference is from cable, especially for the ultra-
sonic level gauge applying two-wire system frequency used, a passive signal isolator
should be used to solve the interference problem.
For meter applying four-wire system, isolated power supply should be applied and
signal isolator should be applied at 4-20ma output part.
If the probe of ultrasonic level gauge is in a connecting pipe, some problems may be
caused as the connecting pipe may amplify the signals. Generally, the height and di-
ameter of the connecting pipe are in proportion, i.e. 5:3. If the height is 200mm, the
inner diameter of connecting pipe will be above 120mm.
8.4 Effects of Connecting Pipe to Measurement
Fig. 11 Echo when Probe is in Connecting Pipe
In the figure above, the base line of echo pattern is very wide, which is caused by
signal amplification by connecting pipe. The echo enclosed by circle is real echo whi-
le the part enclosed by frame is wide base line.
Summary of Contents for LUDP
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