抵抗比偏差から計数値への直接変換構造をもつインテリジェント2線式伝送器

抄録

Microprocessor signal processing is currently incorporated intensively into industrial two wire transmitters. Transmitters are used outdoors under severe environmental conditions. Intelligent transmitters are, therefore, required to have higher accuracy, signal-noise ratio, and temperature stability than those of conventional analog transmitters to satisfy users' expectations.
The key element of an intelligent transmitter is the analog input signal processing including the A/D conversion. Under constraint of low power consumption and single power supply, a direct digital conversion circuit of difference between resistance ratios is developped. The new circuit is achieved by combining both dual slope integrating method and constant voltage driving method of resistive sensor.
This circuit is very stable because it depends only on the stabilities of resistance ratios and on short-term stabilities of electronic parts.
This direct signal processing scheme has been implemented to a mass-produced differential pressure transmitter of Si diaphragm type, and good performances with low temperature co-efficient of 50ppm/°C and high accuracy of 0.1% of full scale.