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HMRC internal manual

Oils Technical Manual

HM Revenue & Customs
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Flow Computers: Temperature, pressure and density


Temperatures are derived from temperature probes which measure thevarying resistance between the probes. These probes are designed to electronically derivethe ambient temperature of the product which then has to be adjusted to ‘standardtemperature’. If this is outside expected parameters, an “alarm” state isinitiated. The action taken in response to an alarm state is dependant upon theconfiguration of the system. The response could be:

  • stopping the product movement;
  • defaulting to a defined temperature until the signal returns to within the expected range;
  • defaulting to a defined temperature until the operator intervenes; and
  • where 2 probes are used the suspect probe readings are replaced by those of the other probe.


Pressure is calculated from the current flowing from in stream transducers. Aswith temperature probes the flow computer monitors the current and flows out with therange and will cause action to be taken similar to the temperature probe failure detailedabove. Pressure does not affect the duty calculation. However if a pressure adjustment ismade to the metered volume this may be removed for duty calculation purposes.


Product density is established by measuring the frequency of thesignal from the densitometer.

Failure procedures similar to those for a temperature probe can be expected.