National Semiconductor SolarMagic, User Manual

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Chapter 3 • Planning
7
3.2 Sensors Overview
Environmental sensors have many applications and therefore many
installation options. Where you locate the sensors for the weather
station is important in order to get accurate data. The sensors should
be located in a clear area on a level surface that represents the general
area of interest, and be away from obstructions such as buildings and
trees
All SolarMagic weather station weather sensors produce a 4–20mA
output signal. 4–20mA is an industrial standard signal for process
control monitoring. Most PLCs (Programmable Logic Controller) and
data acquisition systems accept this signal directly.
The communication module is already connected to the designated
input terminals on the input terminal block in the weather station. The
lead wires from the sensor will need to be connected to the input
terminals in the weather station enclosure. The weather station can be
installed up to 1000ft from the Data Logger and connects through a
twisted pair cable and RS-485 communication (National
Semiconductor recommends a size of stranded copper #18-22 twisted
pair with shielding and drain wire). The weather station also requires
24Vdc, which is typically sourced from the system manager
monitoring kit. The communication protocol is the widely spread
Modbus protocol.
The sensors are sampled continuously to provide real time data. Each
sensor draws between 4mA and 20mA depending on whether the
sensor is reading at the minimum or maximum of its range.
The weather station sensors include an assembly on a sturdy and
durable 1” OD stainless steel tube frame that can be mounted onto a
pre-existing base/mast or onto a tripod for upright installation. The
unit is designed for durability and endurance in harsh conditions. The
Solar Shield, a ventilated sun shield with high reflectiveness, low heat
retention, and low thermo conductivity, is provided as protection and a
mounting platform for the temperature sensor.
Choosing a proper installation location for weather sensors is
important to ensure accurate readings. For example, wind sensors
should not be installed too close to a building, as turbulence created by
the building can interfere with readings. To measure global irradiation
the solar irradiation sensor should be installed in direct sunlight on a
level surface (bubble level and leveling screws are included with
purchase) with similar sun exposure as the PV array.