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Side 64
Ultrasonic Level Meter
Operation Manual
Fig. 9 Echo Pattern under Interference of Frequency Converter
Fig. 6 is interesting. The echo enclosed by circle is real echo and the echo
enclosed by frame is the interference wave of frequency converter. Although
there is interference of frequency converter, the data measured at site is correct
as the echoed signal intensity on water surface is obviously stronger than the
interference signal of frequency converter.
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 connection 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 ultrasonic 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.
IV . Effects of connecting pipe to measurement