TSI's Photodetector Modules (PDM) are used in TSI PDPA/LDV systems for a wide range of particle sizing and flow measurement applications. They combine an interchangeable optics block, called the light bar, with ultra-sensitive photodetectors for maximum ease-of-use and high performance operation. The ultra-sensitive photodetectors exploit the latest advances in PMT technology to convert the scattered light to electrical signals.

A matched set of PMTs is used for phase Doppler measurements. A computer-controlled diode calibration system removes the effects of electronic delays between the three sizing channels and optimizes PDM system operation for particle sizing applications. A diode calibration system generates simulated bursts at any frequency, with very high resolution, to cover the amplitude and frequency range of the signal processor.

The user simply connects the receiving fibers to the PDM light bar. Light bars are easily interchangeable, making it a simple matter to change from LDV to PDPA. The individual channel outputs are available for connection to the signal processor. The PDM also includes a special circuit using a 12-bit A/D converter used to measure pedestal amplitude, which is used for the patented TSI Intensity Validation technique.