Class A pyranometer 3S-IS+

RS-485Modbus RTUwith silicon photodiode

Overview
3S-IS+ is an Advanced Class A irradiance sensor designed for photovoltaic power plants. It measures solar irradiance falling on PV panels in W/m² and helps monitor power plant performance. The unit supports a modular structure allowing connection of additional environmental sensors and transmits measured data via Modbus RTU over an RS485 interface.

How it works
The sensor contains a monocrystalline silicon reference cell. The cell generates current in response to light similar to a PV panel; this current is converted to a measurable signal via a precision shunt resistor. A PT1000 temperature sensor mounted at the back of the cell provides temperature compensation so the electronic board outputs a temperature-compensated irradiance value in W/m².

Diagnostic indicators

• Power LED — Indicates the sensor is powered within the required operating range (typically 12–24 V DC).
• Tx LED — Transmit — Blinks when the sensor is sending data via Modbus RTU.
• Rx LED — Receive — Blinks when the sensor receives a valid Modbus request.

Key advantages

• Class A accuracy compliant with IEC 61724-1 (uncertainty ≤ 1%).
• Modular design enabling integration of module temperature, ambient temperature, wind speed & direction, relative humidity and pressure sensors to form a compact field weather station.
• Reference cell behavior closely matches PV panels for representative measurements.
• Fast response time (1 s standard, can be reduced to 500 ms on demand).
• Easy daisy-chain RS485 connections with an on/off termination resistor option via the device GUI.
• Rugged field design with UV-resistant ASA housing and UV-resistant PUR cable for outdoor conditions.
• Galvanic isolation between power supply and RS485 line and SunSpec compliance.
• 5-year warranty and designed for long-term reliability.

Available models (summary)
All models below are IEC 61724-1:2021 Class A compliant and factory calibrated. The main differences are the number/type of external sensors that can be connected via RS485 Modbus RTU. Models include: 3S-IS+, 3S-IS-1+, 3S-IS-2+, 3S-IS-2T+, 3S-IS-3+, 3S-IS-4+, 3S-IS-5+, 3S-IS-6+.

Models table (concise)
Model: 3S-IS+ — Communication: RS485 Modbus RTU — Uncertainty: ≤1% — External sensors: None
Model: 3S-IS-1+ — Communication: RS485 Modbus RTU — Uncertainty: ≤1% — External sensors: Ambient OR Module Temperature Sensor
Model: 3S-IS-2+ — Communication: RS485 Modbus RTU — Uncertainty: ≤1% — External sensors: Ambient OR Module Temperature, Wind Speed Sensor
Model: 3S-IS-2T+ — Communication: RS485 Modbus RTU — Uncertainty: ≤1% — External sensors: Ambient Temperature, Module Temperature Sensor
Model: 3S-IS-3+ — Communication: RS485 Modbus RTU — Uncertainty: ≤1% — External sensors: Ambient Temperature, Module Temperature, Wind Speed Sensor
Model: 3S-IS-4+ — Communication: RS485 Modbus RTU — Uncertainty: ≤1% — External sensors: Ambient Temperature, Module Temperature, Wind Speed, Wind Direction OR Relative Humidity Sensor
Model: 3S-IS-5+ — Communication: RS485 Modbus RTU — Uncertainty: ≤1% — External sensors: Module Temperature, Wind Speed, Wind Direction, Relative Humidity and Ambient Temperature Sensor
Model: 3S-IS-6+ — Communication: RS485 Modbus RTU — Uncertainty: ≤1% — External sensors: Module Temperature, Wind Speed, Wind Direction, Relative Humidity, Ambient Temperature and Pressure Sensor

Additional information
The irradiance measurement range is 0–1600 W/m². The sensor mirrors panel conditions to allow comparison between expected and actual production and to calculate performance ratio (PR). The enclosure includes diagnostic LEDs and the electronics output data via RS485 Modbus RTU. Each sensor is calibrated under a Class AAA sun simulator using a reference cell calibrated by ISFH (Germany).

Technical specifications

• Product Code: 3S-IS+, 3S-IS-1+, 3S-IS-2+, 3S-IS-2T+, 3S-IS-3+, 3S-IS-4+, 3S-IS-5+, 3S-IS-6+
• Sensor Type: Monocrystalline silicon reference cell (31 mm x 31 mm)
• Measured Data: Irradiance and internal cell temperature; module/ambient temperature, wind speed/direction and relative humidity/pressure via external sensors
• Irradiance Range: 0 – 1600 W/m²
• Uncertainty: ≤ 1% (Class A as per IEC 61724-1)
• Resolution: 0.1 W/m² (Class A)
• Response Time: 1 second (Class A), optionally 500 ms
• Drift: < 0.3% / year
• Field of View: 170°
• Data Output: RS485 up to 38400 Baud
• Communication Protocol: Modbus RTU
• Power Supply: 12 – 30 V DC (24 VDC recommended)
• Power Consumption: Typical 21 mA, maximum 30 mA @ 24 V DC @ 25°C
• Galvanic Insulation: 1000 V between power supply and RS485 line
• Cell Temperature Sensor: PT1000 Class A (EN 60751)
• Cable: 3 m 3x2x0.22 mm², 24 AWG LI2YC11Y-TP PUR cable, UV and weather resistant (6-wire twisted structure including grounding)
• Operating Temperature Range: -40°C to +85°C
• Operating Humidity Range: 0% – 100% RH
• Dimensions: 135 x 105 x 50 mm (W x D x H)
• IP Rating: IP54 (optional IP68)
• Housing Material: ASA (glass fiber reinforced, UV-resistant)
• Calibration: Calibrated under Class AAA Sun Simulator as per IEC 60904-2 and IEC 60904-4 using a reference cell calibrated by ISFH
• Compliant Standard: IEC 61724-1:2021 and IEC 60904
• Origin: Türkiye