In order to make plans for corrosion control of underground metallic structures it is necessary to survey the sheath current and potential against the ground. A current and voltage recording instrument which was designed for making an electrolysis survey is described and field tests results are reported. The instrument consists of a push-pull self-saturation type magnetic amplifier and a conventional electrical recording voltmeter. It was found to perform as follows:
For obtaining 0.6 volt (this corresponds to the full scale 50 mm in the recording meter used), input voltage of the amplifier with Mo-Permalloy cores was 0.48 millivolt for sheath current measurement and 740 millivolts for cable to ground potential measurement in case of the power source of 90 cps with rectangular wave form.
Response time was 7 cycles for current measurement and 4.5 cycles for voltage measurement.
When the source was supplied from the power line (60 cps), the amplification factors decreased about 10 to 35 percent.
The device had good stability, negligible drift and rugged construction. Therefore it is clear that this device is suitable for field test. 4.5.3
