Analogue Voltage Output - Kipp & Zonen SMP series Instruction Manual

Connection to a RS-485 Network
The digital interface can be connected to a 2-wire RS-485 network as shown below.
Balanced pair
LT
Slave 1
The slaves and master may be a SMP pyranometer or other devices. If a SMP pyranometer is the last device on the network a
line terminator (LT), consisting of a 120 Ω or 150 Ω resistor, must be connected between terminals A/A'/- and B/B'/+. Never
place this line termination on the derivation cable. It is also required to install the pull up and pull down resistors as shown.
The value of these resistors must be between 650 Ω and 850 Ω.

2.9.3 Analogue voltage output

The SMP-V (voltage output versions) have been factory set such that an output of 0 Volts represents -200 W/m² (this will never
be reached in practice), and the full-scale output of 1 Volt represents 2000 W/m².
The voltage output range in W/m² can be changed by the user with the supplied PC software. The maximum recommended
irradiance for the SMP3 and SMP6 is 2000 W/m² and for all other SMP's it is 4000 W/m².
The measurement range must start from a negative value in order to show (small) negative readings, for example night-time
o sets, because the analogue output itself cannot go negative. For the default setting of 0 to 1 Volt representing -200 to 2000
W/m² the range is actually 2200 W/m² with a zero o set of 200 W/m².
The irradiance value ( ) for the default setting can be simply calculated as shown below.
E
solar
= Solar radiation
E
solar
V = Output of radiometer [Volt]
If the pyranometer is used in atmospheric conditions it is advised to keep the range as factory set.
Slave n
[W/m²]
Master
Common
20
5 V
Pull up
LT
Pull down