Irradiation Sensors With Modbus RTU Output



A silicon solar cell can be used as an irradiance sensor, because the short-circuit current is proportional to irradiance. Our sensors are built out of a monocrystalline solar cell connected to a shunt. Due to the low resistance of the shunt the cell operates next to short circuit.

The temperature coefficient of the short-circuit current creates a small error.

The compensation is realized by using a specific temperature sensor laminated to the rear side of the solar cell. The measuring signals of short- circuit current of the cell and the resistance value of the temperature sensor are measured by a micro controller.
The calculated values of irradiance and temperature given onto a 4-20mA, 0-10V or RS485 port with customer specification protocol. The electronic circuit is optimized for low power consumption.


The  solar cell is embedded in Ethylene- Vinyl- Acetate (EVA) between glass and Tedlar. Plain integration into the top cover of the box Advanced weatherproof junction box made of UV resistant material with cable gland and screw-less terminal for the connection of the measuring cable, therefore, the sensor construction is comparable to that of a standard PV module. The electrical connection is realized by a 3m cable.

All sensors are calibrated in simulated sunlight against a reference cell of the same type. The reference cell is periodically calibrated against a reference cell calibrated by fraunhofer ise, freiburg.


General Information
Solar Cell Monocrystalline Silicon (52 mm x 52 mm)
Current shunt High precision shunt resistor directly soldered to the terminals of the cell
Operating temperature -30°C to +70°C
Electrical connection via 3 m cable, UV and weatherproof
Power supply 12 to 30 VDC (30 mA typically at 20 VDC)
Interface RS485 up to 19200 Baud
Protocol The sensor is connected via a 2-wire RS485 bus
with open vendor-independent Modbus RTU protocol
Galvanic isolation 1000 V between power supply and RS485 bus
Case, protection mode Advanced weatherproof junction box made of UV resistant material, IP54
Dimensions, weight 94 mm x 94 mm x 57 mm, approx. 200 g
Irradiance 10…1500W/m2, Accuracy of monthly sums
compared to a W.M.O. class 1 Pyranometer (e.g. CMP 11)
according to ISO 9060: better ±5%
Drift Very small drift of <0.3%/ year
Electrical Connection
Color mapping of cable Red (wire) Power (plus) Brown (wire), Black (wire) Power (minus) White (wire),
Brown (wire) Data + / A Green (wire), Orange (wire) Data – / B Yellow (wire),
Black (large profile) Shielding Black (large profile)
Input, Wind Speed 3S-WS-PLS, Wind speed sensor, reed contact, pulse
Input, Ambient Temperature 3S-AT-18B20, Ambient temperature sensor, DS18B20
Input, Module Temperature 3S-MT-18B20, Module temperature sensor, DS18B20
Integrated Module Temp. Integrated module temperature sensor, DS18B20
Calibration Individual calibration of each sensors
in the natural sunlight at AM 1,5 spectrum by means of a compatible
calibrated reference cell.
Handling Case The sensor can be cleaned using a smooth cotton cloth,
water and a mild cleaning fluid. Opening of the sensor case by the user
or installation staff is not necessary. If the case is opened,
we cannot guarantee the seal of the case anymore.
Modbus Specification
Baud Rate 1200, 2400, 9600, 19200, 38400
Parity No, even, odd
Stop Bit 1, 2 (only at no parity)
Factory Default 9600 Baud, 8N1, address: 1



3S-WS-PLS Wind speed sensor, reed contact, pulse Datasheet
3S-AT-18B20 Ambient temperature sensor, DS18B20 Datasheet
3S-MT-18B20 Module temperature sensor, DS18B20 Datasheet
3S-MTG-01 Mounting bracket for Solar Radiation sensor 3S-SR-3T-WS-MB
3S-PS-12VDC Power supply, 220VAC, 50/60Hz, 12VDC, 300mA
3S-Shield-A Solar Radiation Shield for Ambient Temperature Sensor PT100, PT1000, DS18B20 etc. Datasheet