Precision Filter Radiometer (PFR)

The main focus of the PFR re-design was to include backward compatibility with existing instrument holders and data acquisition systems. Improved features are an upgraded sensor head. In the PFR-19 design (see Figure 1), great effort went into the modular construction. The main objective was to develop an efficient instrument assembly process as well as a reduction in maintenance and repair interventions. The design of the optical filter holder was standardised and now allows the installation of different optical filter types during assembly. In this way, the instrument serves as a base instrument which can be adapted for different wavelengths with only minor hardware adjustments.

To keep the optics inside the instrument as clean as possible, low outgassing materials are used, e.g. PTFE (polytetrafluoroethylene) isolated wires. Similarly, in order to reduce the formation of particles from shutter wear, the mechanics of the shutter were improved so that no mechanical stops are necessary.

On the electronics side, the focus was on instrument safety. On that account, input protection circuits, which provide over and under-voltage as well as short-circuit protection, were introduced on all in/out connections to the sensor head. Partial power loss is also handled and results in a safe shut-down of the sensor head. The second objective was to decrease noise on the diode and housekeeping signals. In order to do so, the power electronics, namely the Peltier system, is now wired directly to the main PCB which comprises the control circuit. In the external data acquisition electronics box, the 230V AC-DC power supply was replaced with a linear one so that high frequency switching noise and its harmonics do not affect the instrument. The remaining signal noise is further reduced by efficient low-pass filters on all signal amplifiers, which cut off undesired frequencies higher than 5 Hz. Finally, a gain-switched amplifier was re-introduced into the diode signal path, which allows gain change to optimise the full-scale measurements, thus enabling a higher signal resolution over a period of a full day (sunrise to sunset).

An initial batch of ten PFR-19 were assembled, and will replace defective instruments from the GAW-PFR network. Another batch of commercial PFRs was prepared for interested external PFR users. Subsequent PFR series will be built, depending on commercial orders from the scientific community.

A future development will include a high-sensitivity version of the above solar PFR for measuring lunar irradiance during night-time AOD measurements.

Full details can be found in the PFR-19 specifications sheet →

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