Low power, high accuracy angular deviation measurement system


Technology abstract

A Belgian company with extensive expertise in vision and optical metrology has developed a system with Solar Ecartometry Sensor (SES) for high accuracy angular deviation measurement of a lightsource.

The system has successfully undergone a qualification process for the optical performance: centering of the optical axis, field of view, angle accuracy and depointing resolution. Other design aspects: radiation hardening, small footprint and low power.

Technology Description

This sensor was engineered by a Belgium company boasting a wide-ranging expertise in the field of vision and optical metrology.

The system is composed of a sun imaging system, a 4-quadrant detector, a set of filters that select a narrow wavelength range and adjust the flux on the detector, electronics converting the photocurrents into 4 voltages and dedicated software for highly accurate sun position tracking.

Critical in the design to minimize measurement errors are the selection of the wavelength (782nm +/- 5nm), minimization of darknoise, minimization of the gap between the 4-quadrants of the sensitive area’s to 10µm.

Other design aspects included radiation hardening, small footprint and low power (6mA @ 5.3Vmax)

The imager consisting of 4 quadrant detectors, has been designed for a central wavelength of 782 nm +/- 5nm and is diffraction limited over the full field of view (+/- 780 arcsec) with a distortion of less than 0.0001%. The clear aperture of the system has been limited to 13.3mm.

The image of the sun partly covers the 4 detectors. For a square spot, the position on the sensor can easily be derived. However, a complex equation was developed to correct positions of a circular spot taking into account the actual gap value between the detectors.

The lens system is made out of radiation resistant glass to limit measurement variations over its lifetime. It comprises 3 filters (attenuation, wide band, fine wavelength selection) designed for flux attenuation and wavelength selection. Lenses are auto-centered to avoid misalignment due to vibration and thermal constraints. The housing is made of Aluminium and Vespel.

The electronics operate within a voltage range of 4.5 – 5.3V and consume 6mA. They are designed to amplify (2-stage amplification) the photocurrents and convert (I-V converter) them in a voltage covering a range of 4V. Saturation is reached when the spot is shifted by one radius at 45° of the quadrants.

Thermal operating range of the SES (both mechanics and electronics) is -40°C to +60°C.

Innovations & Advantages

  • Very small gap between sensor quadrants with software algorithms to correct for the actual value of the gap.
  • Higher sensitivity than existing angular position sensing devices for lightsources.
  • The entire system including optics, imager, electronics, algorithms, software and calibration/qualification equipment has been designed in-house, and can be adapted for integration into other products.
  • Knowhow can be applied to other dedicated high precision applications using other OTS quadrant sensors.

Other design aspects included radiation hardening, small footprint and low power.

Further Information

  • Absolute accuracy: 5 arcsec
  • Resolution: 1 arcsec
  • FOV: +/-780 arcsec
  • Operating Voltage: 4.5-5.3V with +/-100mV noise)

Power consumption: 6mA

Current and Potential Domains of Application

This sensor and/or knowhow could have potential applications in fields where:

  • COTS quadrant sensors do not offer the required performance
  • COTS quadrant sensors do not offer the required characteristic or output

  • High altitude research and telecommunication
  • Applications using quadrant position sensors having special performance and or processing requirements
  • Laser tracking devices
  • Quality control
  • Telemetry
  • Microscopy
  • Telescopy
  • Aircraft tracking