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3.3
ELECTRICAL CONNECTION
The CM 4 is provided with a special 10 m cable with six leads and a
shield covered with a black sleeve.
The colour code is:
Pt-100 temperature sensor (4 – wire connection)
The shield is directly connected to the case. Preferably the shield
should be connected to the same ground at the readout equipment,
to reduce cable noise. The cable must be firmly secured to minimise
spurious response during any mechanical movement or vibration
(pressing the cable produces voltage spikes, a tribo-electric effect
and capacitance effect).
Looking at the circuit diagram of figure 3.1, it is clear that the
impedance of the readout equipment is loading the thermistor circuit
and the thermopile. This can increase the temperature dependency
of the pyranometer. The sensitivity is affected more than 0.1% when
the load resistance is less than 1.5 MΩ. For this reason we
recommend the use of readout equipment with an input impedance
of 1.5 MΩ or more, such as potentiometric recorders, digital
voltmeters, etc. The solar integrators and chart recorders available
from Kipp & Zonen meet these requirements. Extension cables may
be used, but the cable resistance must be smaller than 0.1% of the
impedance of the readout equipment.
red
=
plus
blue
=
minus
Shield
=
case
White:
Pt 100 (combined with black)
Black:
Pt 100 (combined with white
Green:
Pt 100 (combined with yellow)
Yellow:
Pt 100 (combined with green)
3. INSTALLATION
23
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