CS325DM-L Silicon Irradiance Reference Sensor


The CS325DM-L, manufactured by Atonometrics as the RC18, is a silicon solar irradiation sensor commonly used as a “reference cell” in solar photovoltaic (PV) monitoring applications. This solar radiation sensor has a temperature operating range that allows it to work effectively in different environments. The sensor element was designed to correspond to PV modules, including spectral selectivity and incident angle modifier. The data signals are Modbus RTU RS-485 or analog.

Benefits and Features

  • Rugged design with wide temperature operating range
  • Analog and/or digital outputs available
  • Spectral selectivity and incident angle modifier correspond to crystalline PV module
  • Built-in cell temperature measurement and signal compensation

A user guide is available for download from the manufacturer of the CS325DM.



Sensor Silicon solar irradiation sensor
Measurement Description Solar irradiance measurements for outdoor monitoring of PV systems
Irradiance Measurement Range 0 to 1500 W/m2
Operating Temperature Range -35° to +80°C
Input Power 8 to 28 Vdc (12 to 28 Vdc for 0 to 10 V analog output)
Photovoltaic Cell Crystalline Si, 20 mm x 20 mm, ~135 mA @ 1 sun
Window Low-iron solar glass, or CdTe-matching filter
Cell Temperature Measurement -40° to +100°C, Pt100 RTD
Calibration Data Internally calibrated; no calibration data to manage
Enclosure Material Powder-coated cast aluminum housing
IP Rating IP67
Cable Type Shielded, weather-resistant, UV-rated, 24 AWG/0.2 mm2
Cable Connector M12 circular connector, IP67
Response Time 0.15 s
Electronics Non-Linearity ±0.03% of range
Repeatability ±0.02% of range
Temperature Drift ±0.4% at 1000 W/m2 (-35° to +80°C)
Factory Calibration of Electronics ±0.1% of reading ±0.2% of range
Irradiance Calibration ±1.8% (calibrated to NREL-traceable reference standard)
Overall Measurement Uncertainty ±2.0% of reading ±4 W/m2
Stability 0.5% per year
Mounting 4 mounting holes with diameter 5.50 mm (0.217 in.)
Dimensions 115.1 x 65.0 x 30.0 mm (4.53 x 2.56 x 1.18 in.)
Weight 0.3 kg (0.6 lb)


Communications Protocols Modbus over RS-485, user-settable Modbus address
Baud Rate Up to 57.6 kbps
Current Consumption Typically 8 to 15 mA


Analog Output Options
  • 0 to 1.5 V
  • 0 to 10 V
  • 4 to 20 mA
Analog Output Signals
  • Irradiance
  • Cell temperature
  • Short-circuit current
Current Consumption
  • Typically 8 to 15 mA (0 to 1.5 V or 0 to 10 V mode)
  • 15 to 55 mA (4 to 20 mA mode)
Output Impedance 2 kohm (0 to 1.5 V or 0 to 10 V mode)
Internal Voltage Drop Allow 3.5 V minimum (4 to 20 mA mode)


The CS325DM requires an RS-485 adapter if the data logger it is being used with does not support RS-485.


CS325DM Program Examples v.2 (3 KB) 11-01-2022

Two CR1000X data logger programs that read the CS325DM measurements. An example program is included for each output option (digital Modbus, analog). Program code for other data logger models will be similar. 

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