Electrical Connections; Power Connection - Kipp & Zonen SMP series Instruction Manual

2.9 Electrical connections

As standard SMP pyranometers are supplied with a waterproof connector pre-wired to 10 m of high quality yellow cable with 8
wires and a shield covered with a black sleeve. Longer cables are available as options. The colour code of the wires and the
connector pin numbers are shown below and on the instruction sheet.
Special attention is needed to prevent power or ground loops when connecting the SMP to multiple readout devices.
Connecting the RS-485 to a grounded circuit and the analogue output to a floating circuit can cause unacceptable
ground loops. This may cause di erential voltages outside the SMP specifications and will damage the unit. We
recommend using either the analogue or the digital output but not both. The maximum di erential between either
of the Modbus® RS-485 lines (yellow and grey) and the power ground / RS-485 common line (black) is 70 VDC.
First connect all wires before plugging into the radiometer
The shield of the cable is connected to the aluminium radiometer housing through the connector body. Preferably,
secure the radiometer with its levelling screws on a metal support with a good connection to ground (e.g. by using
a lightning conductor) and do not connect the cable shield at the readout end.
If there is no good ground connection at the pyranometer, the shield at the cable end should be connected to ground
at the readout equipment. Lightning can induce high voltages in the shield but these will be led o at the pyranometer
or readout equipment.
Note Long cables may be used, but the cable resistance must be smaller than 0.1 % of the impedance of the readout
equipment for the analogue outputs and may a ect the baud rate of the RS-485 digital connection.

2.9.1 Power connection

The minimum power supply voltage for SMP pyranometers is 5 VDC. However, for optimal performance it is advised to use
12 VDC, especially when long cables are used. 5-volt power can only be used in combination with a short cable, maximum 10 m.
It is advised to protect the output of the power supply with a fast blowing fuse of maximum 250 mA rating.
3
V / mA 6
4
5
SMP-V or SMP-A
7
8
Modbus® RS-485
1
2
5 to 30 VDC
power supply
18
Radiometer Connection
Wire Function Connect with
Green Analogue out V+/4-20 mA(+)
Brown Analogue ground V-/4-20 mA(-)
Yellow Modbus® RS-485
Grey Modbus® RS-485
White Power 5 to 30 VDC
(12 V recommended)
Black Power ground / RS-485 Common
Red None Not connected
Blue Modbus® common / Ground
Shield Housing Ground *
* Connect to ground if radiometer not grounded