Description
The SMP21 is a secondard standard pyranometer that combines the sensor technology of the CMP21 with the added benefits of the both a RS485 Modbus interface and a standardised analogue output. The SMP21 uses a 32-junction thermopile sensing element under two, 2mm thick, high quality concentric domes which reduces directional error and improves thermal isolation. The housing include a screw-in drying cartridge that can simply be removed using a coin. This allows the desiccant to be replaced on site without the need for specialist equiment. Convenient desiccant refill packets are available to make this process as simple as possible.
The housing design of the SMP 21 is designed with a sensor to monitor the housing temperature and the SMP 21 uses a passive temperature compensation circuit with a standardised linear function to allow for individual temperature compensation. Each instrument is supplied with its own individual temperature and directional response data for improved post processing of recorded data. This individualised data is the reason the SMP21 is the choice for scientific use and in top level solar radiation monitoring networks such as the Baseline Surface Radiation Network (BSRN) and Global Atmospheric Watch (GAW) of the World Meteorological Organisation (WMO).
The SMP21 come with a 0-1V or 4-20mA analogue output and these can be rescaled by the user with the supplied PC software. The units are configured with the 0-1V output set as -200 to 2,000Wm² and the 4-20mA output as a 0-1,600Wm². Negative ranges are provided to allow the sensor to show levels at night when there is heat emitted from the sensor. All SMP’s have the RS485 Modbus RTU interface, very low power requirements and are supplied with comprehensive, traceable, calibration certificates. Calibrations are traceable to the World Radiometric Reference (WRR) in Davos Switzerland and are performed in accordance with ISO 9847, Annex A.3 ‘Calibration of Field Pyranometers by comparison to a Reference Pyranometer’.
Diagram
Specification
| ISO 9060:1990 Classification | Secondary Standard |
| Spectral Range | 285 to 2800nm |
| Response Time | <2s |
| Zero Offset A | <7 W/m² |
| Zero Offset B | <2 W/m² |
| Directional Error | <10 W/m² (Up to 80º with 1000 W/m² beam) |
| Temperature Dependence of Sensitivity | <0.3% (-20 to 50°C) <0.3% (-40 to 70°C) |
| Analogue Output | -V version: 0-1V -A version: 4-20mA |
| Analogue Output Range | -V version: -200 to 2000W/m² -A version: 0 to 1600W/m² |
| Digital Output | 2 wire RS485 Modbus RTU |
| Digital Output Range | -400 to 4000W/m² |
| Operating Temperature | -40 to +80°C |
| Supply Voltage | 5 to 30vDC |
| Power Consumption (at 12vDC) | -V version: 55mW -A version: 100mW |
| Ingress Protection | IP67 |
SMP21 instruments have an 8-pin socket and can be connected to a standard cable with a pre-wired waterproof 8 pin plug and flying leads. Cable lengths of 10m, 25m, 50m and 100m are available.