Description

The CHP 1 Pyrheliometer is an all-weather pyrheliometer available for continuous measurements of direct solar radiation. The CHP 1 exceeds the specifications for high end solar radiation networks, such as the Baseline Surface Radiation Network (BSRN) of the World Climate Research Programme (WCRP). These networks require accurate and reliable long-term measurements for climate change investigations.

A pyrheliometer is an instrument designed specifically to measure the direct beam solar irradiance with a field of view limited to 5°, also known as Direct Normal Irradiance, DNI. This is achieved by the shape of the collimation tube, with precision apertures, and the detector design. The front aperture is fitted with a quartz window to protect the instrument and to act as a filter that passes solar radiation between 200 and 4000nm in wavelength.

The CHP1 consists of a thermopile detector and two temperature sensors mounted at the rear of a collimation tube. The thermopile responds to the total power absorbed by the black surface coating, which is a non-spectrally selective paint, and warms up. The heat generated flows through a thermal resistance to the heat-sink (the pyrheliometer body). The temperature difference across the thermal resistance of the detector is converted into a voltage as a linear function of the absorbed solar irradiance. The CHP1 will produce a maximum output of 25mV under normal atmospheric conditions.

The detector is similar to that used in the highest level pyranometers CMP21 and CMP22, which minimizes the influence of ambient temperature fluctuations and provides a fast response time. Both PT100 and 10K thermistor temperature sensors are fitted as standard, to allow use of the individual temperature response data supplied with each CHP 1. Thanks to the signal cable connector and screw-in desiccant cartridge the design is easy to install and maintain. The specifications exceed ISO and WMO performance criteria for First Class Normal Incidence Pyrheliometers. Every CHP 1 is supplied with a calibration certificate traceable to the World Radiometric Reference and is valid for 1 year from the first use.

Specification

The CHP 1 has a maximum output of 25mV under normal atmospheric conditions and it is recommended that a data logger with an analogue input of at least 12 bits resolution over that range is used to record the readings.