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Doc No. DCP0000518 JH 12/7/99 rev2
To calculate the required current it is first
necessary to calculate the aspect ratio of the
loop. This is the width of the loop divided by the
length of the loop, assuming the loop approxi-
mates to a rectangle. Circular loops should be
approximated to a square. If the room is L -
shaped, assume it is a square or rectangle and
use the longest side and the longest width. (For
this case, the calculated peak current required
will be too large, so reduce the drive level slightly)
It is also necessary to know the total length of the
loop cable. If the connecting cable from the
amplifier to the loop is the same cable as used
for the loop, then this should also be included.
The calculations below assume that the
loop will be approximately the same level as the
receiver. (Vertical displacement) If the loop is
significantly higher or lower (more than one to
two metres) than the receiver, then the peak
current required will be slightly higher.
Peak current calculation
Refer to the current width- graph to estab-
lish the required peak current. The width of the
loop is shown on the x-axis. The peak current is
shown vertically on the y-axis.
This is the peak current. The average
current output should be approximately one
quarter of the maximum peak.
Move along the x-axis until you come to the
width of your loop, then move up until you come
to one of the aspect ratio lines. From this point,
read the peak current required.
The D.C resistance of the loop should be
between 0.2 Ohms and 2 Ohms. It is very un-
likely that any loop will be less than 0.2 Ohms as
this is virtually a short. It is quite acceptable to
have a D.C resistance greater than two Ohms,
but full current drive may not be possible.
Peak current calculation
