Temperature data transmission via plastic optical fiber in environmental test setup

This paper describes the optical fiber transmission of digital temperature data in the range of -20°C to 100°C which are acquired in an environmental test chamber. Temperature data acquired by a p-n junction sensor whose sensitivity is 1 μA/degree is converted into digital data of 8 bits using an A/D converter. High order 4 bits of digital data are assigned to four multifrequency sine-wave signals on the high order channel, and low order 4 bits of digital data assigned to other four multifrequency sine-wave signals on low order channel. Each channel consists of 4 bits which correspond to multifrequencies at 135 kHz, 250 kHz, 370 kHz, and 520 kHz. AM carriers at 7.0 MHz and 11.0 MHz respectively modulate multifrequency signals on the respective channels before sent to the AM mixer which combines two channels in order to generate data of 8 bits. The mixer output is fed to an E/O (electrical-to-optical) converter to convert them to an optical signal. The optical signal is fed from the sender to the receiver via a plastic optical fiber. The optical signal is converted to the original electrical signal at the receiver using an O/E (optical-to-electrical) converter. Data is reproduced by a D/A converter at the receiver, and displayed on a data recorder. The resolution of temperature data was 0.4 degrees in the A/D and D/A converters. Noises and spikes caused by the grounding current of the test setup were not recognized at the receiver. Temperature data in a cyclic temperature test was acquired to confirm the reliability of the environmental test chamber. Temperature data of a heat sink mounting tree MOSFETs which dissipated approximately 200 W in total was acquired by the temperature sensor