Eglin Team 3

Results:

After attempting to integrate our system with the current system, the Edmund Optics photo-receiver modules did not function as aspected. The photodiode output voltage change response time was to slow. As the projectile traveling at approximately 200m/s passed through the barrier, the voltage change from the detectors was not high enough to be detected. An investigation into to the cause for the malfunction revealed that the time to peak voltage for the photodiodes contained within the detectors was 300μs. At a velocity of 200m/s the sensors will only be blocked for 10μs. With this short time the voltage will only rise roughly one thirtieth of the maximum voltage which is 0.3V. This level is immeasurable. The photodiode rise time was a factor used when the group designed a system but was overlooked with the Edmund optics design because it was the only viable packaged system within the project budget and the photodiode type was not optional.
After the failure of the onsite test, the team was provided with the schematic and operating procedure for the currently installed detectors. After review of the manual the group identified two recommendations to repair the current detectors for relatively low cost. Unfortunately due to time constraints the group was not able to enact the corrective actions.

1. Replace the detector photodiodes. The diode is available from Roithner Lasertechnik for $14.89. The photodiodes in use were installed have been in use for twenty years and are nearing their end of life.

2. Replace the Helium Neon Lasers. The lasers intensity decreases with time. According to the operations manual page 6 the lasers have a life span of 2 years and have been in service for twenty. The cost of a new helium-neon laser is estimated at $700.00.

Additional research has identified an entire direct replacement system. The system is manufactured by MS Instruments and is known as the Type 858 Optical Detector. The system costs an estimated ₤8,000.00. The system utilizes the same principles as the group design photodiode optical barrier system. The system can measure projectile velocities with a velocity of 5-5000m/s with a 1% error.