Description
The housing design of the CMP 21 is fitted with a screw-in drying cartridge that can simply be removed using a coin. This allows the desiccant to be replaced as required using the convenient refill packets. The CMP 21 also features a passive temperature compensation circuit with a standardised linear function.
The CMP 21 has a 32-junction thermopile sensing element, which features faster response, better linearity and a wider measurement range than the CMP 3 and CMP 6. Additionally, the CMP 21’s are individually optimised for temperature compensation and each sensors includes a separate 10K thermistor, or PT100 sensors to monitor the housing temperature for post-processing compensation adjustments.
The integral bubble level is raised to the top of the housing and can be viewed without removing the redesigned snap-on sun shield, which also covers the connector. The connector with gold-plated contacts allows for easy exchange and re-calibration.
It is the choice for scientific use and in top level solar radiation monitoring networks such as the BSRN (Baseline Surface Radiation Network) or WMO (World Meteorological Organisation).
Diagram

Specification
| Classification to ISO 9060:2018: | Spectrally Flat Class A | 
| Sensitivity: | 7 to 14µV/W/m² | 
| Expected Output (0-1500W/m²): | 0 to 21mV | 
| Response Time (95%): | <5 Seconds | 
| Spectral Range (50% Points): | 285 to 2800nm | 
| Zero offsets (unventilated) (a) thermal radiation (at 200W/m²): (b) temperature change (5K/h):  | 
< ±7 W/m² < ±2 W/m²  | 
| Non-Stability (Change/Year): | <±0.5% | 
| Non-Linearity (100 to 1000W/m²): | <±0.2% | 
| Direction Response: | <±10W/m² | 
| Temperature Response: | <±1% (-20 to +50°C) | 
| Field of View: | 180° | 
| Detector Type: | Thermopile | 
| Operating Range: | -40 to +80°C (0-100%RH) | 
				