W&T
48
Using a copper cable with a cross-section of 0.75mm² and a
length of 100m, the cable impedance will be 4.6 ohms, which
is within the tolerance range.
For copper cables verify the impedance using the following for-
mula:
The result of this calculation must lie below 10 ohms.
More critical than the cable length are the external noise
effects on the cable. This can result in inaccurate rea-
dings. Be sure therefore that the cable is isolated from
other installations and thus not subjected to electroma-
gntic radiation. Twisted-pair cable (e.g. Cat.5) wil also help to
suppress noise.
!
The accuracy and noise immunity of the sensors
d e p e n d o n t h e c a b l e l e n g t h a n d a n y n o i s e
sources which may be present. This means that the
local conditions of some installations may, if not rectified,
result in measuring errors or inaccuracies. For a new
installation, we recommend using a 4-conductor cable in
order to allow for later use of PT100 technology.
We have taken a number of steps in order to ensure that
noise sources such as 50Hz interference from the AC ca-
ble does not have an effect on the measured values. You
can easily check to see how effective our noise suppres-
sion is working in your environment by using fixed resi-
stors instead of NTC sensors. The measured values
should in this case fluctuate by a maximum of 1 decimal
point.
2 length [m]
58 cross section [mm²]
R
L
=
