Design and implementation of an automated measuring system for a goniophotometer

Abstract

The IES (Instituto de Energía Solar, spanish for Institute of Solar Energy)
of the Universidad Politécnica de Madrid (Technical University of Madrid)
decided to build a goniophotometer, which is an instrument to measure the
angular dependence of a photometric quantity. Although the purpose of this
decision is local quality testing, it is planned to be replicated in countries
where the IES has rural electrification projects.
The aim of this project is to design the automated measuring system for
that goniophotometer. As it is intended to implement this design in different
geographical locations, it must be as replicable as possible, i.e., the lesser the
dependence on a specific component, the better. In consequence, an architecture was designed instead of a particular automated measuring system.
This way, by using similar components, it can be implemented anywhere in
the world. However, as a proof of concepts (and to be used at the IES), this
project also involves an implementation of that architecture.
Concerning the IES goniophotometer, it is a fixed-sensor, moving-light
source, type C goniophotometer: Two motors rotate the light source in the
polar and azimuth axes while a sample of the illuminance fallen on a sensor
is taken in all directions. Afterwards those samples are converted into luminous
intensities using the inverse square law, and the total luminous flux is
calculated from them.
The resultant architecture of the automated measuring system was named
after its only non-generic and core element: KNDL. It is a freely distributed
Java program developed during this project. Its purpose is to collect, sort,
process, and store the measured data. These data are received from a control
device (i.e. a microcontroller) which orchestrates the rest of the elements:
two reference subsystems, two stepper motors (and their respective motor
drivers), and a sensing subsystem.
For the implementation an Arduino Board was used as a control device,
an optocoupler and a metallic disk with a notch for each reference subsystem,
two H-bridge motor drivers, two bipolar stepper motors, and two types
of sensing subsystems: A separated lux meter and an analog-to-digital converter, and an integrated circuit.
Finally, a few light sources were measured in order to generate results.
Two set of tests were performed: One to compare plots of the resulting luminous
intensity distribution with the shape of the light sources, and another
to compare the resulting total luminous flux of the light sources with that of
another system (more specifically, an integrating sphere).