13
W
1ELA
H
BM
A2621−10.en/de
7
D
isturbing effects
The carrier frequency method is by nature to a large extent immune to electri
cal interference. In spite of this, interference at high intensity can falsify the
measurement. A typical disturbance arises if the amplifier cannot be zero−bal
anced at the zero position of the sensor.
The disturbance can enter the measuring circuit:
− electromagnetically − inductively
− galvanically
− mechanically
Recognizing the source of interference is the prerequisite for taking rational
countermeasures. Interference is caused chiefly by:
− heavy current lines parallel to the measuring conductor
− relays (contactors) in the vicinity
− electric motors
− potential differences in the grounding system or multiple grounding of the
measuring system
− vibrations
7.1
Shielding
Electrical interference in the high−frequency range can be reduced by using
shielded cable.
H
BM measuring cable provides appropriate shielding and, in
addition, a symmetric and low−capacitance design.
7.2
Grounding
Multiple grounding of sensor, amplifier and indicating instrument, might poss
ibly result in ground loops" that falsify the measurement result or make it im
possible to measure small signals.
Prior to a measurement you should therefore check if there are any interferen
ces caused by ground loops. For this purpose, first establish an electrically
conductive connection between sensor and measuring object and bring the
plunger into center position (observe the amplifier’s balancing range). If the
sensor now can no longer be zero−balanced this interference signal might
possibly be reduced by providing a positive ground.
