Inductive coupling -fixing by twisted pair
This form of spurious coupling is prevented by using either twisted pair conductors or coaxial cable (coax method described on next page). Figure 8 shows use of twisted pair (note that here only one pair of many twists is shown). As seen in Fig. 8, each successive twist segment has a linked flux opposite in polarity compared to the previous segment resulting in no net linked flux. If the top and bottom circuits have identical adjacent twisted pairs, then the effect of twisting will be undone and the adjacent twisted pair cables will strongly couple to each other. Category 5 cable avoids this by having the twist periodicities in adjacent cables proportional to different prime numbers so the twists never line up with each other
Figure 8 Magnet field (blue) produced by current (red) in top circuit links bottom circuit. The time derivative of the linked flux (magnet field times area) produces a voltage in the bottom circuit. This spurious voltage adds to the voltage from the sensor in the left-hand twist element in the bottom circuit and subtracts from the sensor voltage in the right-hand twist element so there is no net contribution from the linked flux.