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HMRC internal manual

Oils Technical Manual

HM Revenue & Customs
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Measurement: telemetering

Electrical systems are normally used for transmitting the readings of automatic tank level gauges and related equipment to remote points. Since the voltage and the current can be affected by external disturbances, direct current measurement is used only if adequate safeguards can be applied. (IP 252/76 provides for appropriate standards at different levels of specified security).

Most telemetering systems depend on the number of (or the time interval between) electrical pulses generated mechanically or electrically. Spurious pulses may be produced by external electrical interference, caused for example by the close proximity of the transmission lines to power cables or telephone lines. Safeguards are required to prevent the transmission of spurious pulses and to ensure that the amplitude of pulses arriving at the remote point is adequate for accurate reading.