Kipp & Zonen CM 11, Instruction Manual

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INSTALLATION
31
A considerable input bias current of the readout equipment can produce a
voltage of several microvolts across the impedance of the pyranometer. The
correct measured zero signal can be verified with a resistance replacing the
pyranometer impedance at the input terminals.
The pyranometer can also be connected to a computer or data acquisition
system. A low voltage analogue input module with A to D converter must be
available then. The span and resolution of the A to D converter in the module
must allow a system sensitivity of about 1 bit per W/m
2
. More resolution is not
necessary during outdoors solar radiation measurements, because
pyranometers exhibit offsets up to + or - 2 W/m
2
due to lack of thermal
equilibrium.
A surge arrester is installed to conduct induced lightning currents to the case.
It is recommended to ground the case for this reason. The surge arrester is
noble gas filled, has infinite impedance and recovers after breakdown.
Breakdown voltage is 90 V. Peak pulse current is 10 kA.
For amplification of the pyranometer signal Kipp & Zonen recommends the CT
24 amplifier, available from Kipp & Zonen. This amplifier will convert the
microvolt output from the pyranometer into a standard 4 – 20 mA signal.
Voltage output and amplification adjustment to the pyranometer calibration
factor are also possible.
3.3.1 Electrical connection CM 14
The CM 14 is provided with a 10 m cable with shield and five leads.
The colour code is:
red :
+ upper sensor
blue : - upper sensor
green : + lower sensor
yellow : - lower sensor
white : case
There are two modes of operating an albedometer: