| 摘要 |
A two-wire type converter in which voltage signals detected by a detecting element of a pH meter, for example, are converted into current signals and the resulting current signals are transferred to an indicator of a measuring device or the like through a two-wire type transmission channel which also serves as a feed line of electric power for driving said converter. The two-wire type converter includes a first system which is physically located nearby a detecting element and a second system which is physically located far from the detecting element. The systems are electrically insulated from each other by means of a first insulated transformer and a second insulated transformer. The first system includes a phase modulation circuit consisting of a voltage comparator, a square wave oscillator, a first phase comparator and a first integrator circuit. The second system includes a demodulating circuit consisting of a reference square wave oscillator, a second phase comparator, a second integrator circuit and a voltage/current converter. The first system also includes a rectifying circuit and a voltage stabilizer for use as a power supply for driving the phase modulation circuit. Electric power is supplied from the reference square wave oscillator to the power supply through the first insulated transformer. The second system also includes a voltage stabilizer for use as a power supply for driving the demodulating circuit and square wave oscillator. Electric power is supplied from the two-wire type transmission channels to the voltage stabilizer.
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