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3.3
ELECTRICAL CONNECTION
The CM 11 is provided with a 10 m cable with three leads and a shield
covered with a black sleeve.
The colour code is:
red
blue
white
The shield is isolated from the case, so no shield-current can exist. Shield and
white lead may be connected to the same ground at the readout equipment.
The cable must be firmly secured to minimise spurious response during
stormy weather (pressing the standard cable produces voltage spikes, a tribo
electric effect and capacitance effect).
Kipp & Zonen pyranometer cables are of low noise type, however take care
that the terminals '+' and '-' at a connection box have the same temperature,
to prevent thermal EMF's. A box or connector with metal outer case is
advised.
Looking at the circuit diagram of figure 14, it is clear that the impedance of the
readout equipment is loading the thermistor circuit and the thermopiles. It can
increase the temperature dependency of the pyranometer. The sensitivity is
affected more than 1% when the load resistance is under 150 kΩ. For this
reason we recommend the use of readout equipment with input impedance's
of 1 MΩ or more such as potentiometric recorders, digital voltmeters, etc. The
solar integrators and chart recorders from Kipp & Zonen meet these
requirements. Long cables may be used, but the cable resistance must be
smaller than 0.1% of the impedance of the readout equipment.
Kipp & Zonen supplies shielded low-noise extension cable up to lengths of
200 m. This extra length can be supplied fitted to the pyranometer when
ordered, or can be coupled by waterproof connectors to the CM 11 cable. The
lead resistance is 8 Ohm/100 m.
=
plus
=
minus
=
case
INSTALLATION
29
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