The Design Of Illuminance Measurement System

The illumination measurement and application are more and more widespread in these related fields of photography project, medical and health, lighting project and traffic safety project. The requirements for illuminance measurement system are not limited to the accuracy, but also in terms of functionality which had been required the diversity and intelligent. An illuminance measurement system was designed in this paper. The master of the system is SCM AT89C52. The character of system is automatic range switching, automatic adjustable gain, high accuracy, and low-cost. At the same time, the system not only can measure the static light source but also measure the peak illumination on the dynamic light source.A new method on dynamic gain adjustment was proposed according to the difference illumination characteristics between the dynamic light and static light sources. By using this method on dynamic gain adjustment combined with the method of range interval control, the static light illumination measurement and the dynamic light sources illumination measurement when in the peak time were achieved. The main contents of the paper included following five sections:(1) The pre-amplifier circuit was designed on photoelectric conversion:the silicon photocell was used as a detector in the paper. The output photocurrent of the silicon-solar cell is very weak in the photoelectric conversion process. Therefore, the weak current must be pre-amplified, But the analog-to-digital converter need input voltage signal, the preamplifier should be designed to the form of the current-voltage converter. (2) The design of the automatic range converter circuit: Because of the generated photocurrent is too wide in the illumination range 0.0001lx-2000lx, so, the illumination range is divided into four intervals. The switch between different illumination intervals was achieved by the microprocessor controlling the analog switches CD4051. (3) The design of intensity measurement method on dynamic and static light sources:The static light illumination measurement and the dynamic light illumination measurement in the peak luminous intensity were completed by the method on dynamic gain adjustment combined with the range interval control. (4) The design of the keyboard and display circuit:The matrix keyboard and digital tube display circuit were designed in this paper. (5) The software design on illuminance measurement system:The software design on the system included the software design on automatic range switching, the software design on the serial communication between single chip computer and CS5531, the software design on static and dynamic light sources illumination measurement, the software design on keyboard identification, the software design on digital display and the communication between SCM and PC.Through designing the hardware circuit and debugging the software program on the illumination measurement system, the system basically met the design requirements in these two areas for the measuring range is 0.0001 lx-2000 lx and the accuracy is 1% of full scale, at the same time, the static light illumination measurement and dynamic light source intensity peak illumination measurement were completed.