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Technical information

The calorimetric principle

Unlike other methods of operation the calorimetric principle of FlowVision flow monitoring systems, which relies upon heat dissipation measured between two sensors, can be used to monitor the rate of flow of almost all media capable of moving through a pipeline, irrespective of their electrical conductivity, density, viscosity and contamination, and within a wide range of temperatures and pressures.

For accuracy of operation, calorimetric flow monitoring systems must convert a specific flow rate into a consistently equivalent voltage. To meet this requirement, FlowVision monitoring heads are equipped with two sensors, one of which is used as a temperature reference.

FlowVision monitoring heads are sophisticated high-precision sensors. Approximately parallel temperature response curves of the sensors are ensured by keeping the thermal contact resistances as small and constant as possible: The more parallel the temperature curves of the two sensors, the lower the temperature drift.

CP-method (Constant Power): Types SW and FS

The calorific power of the body is kept constant. The volume flow is determined by measuring the temperature difference between the two sensors. All FlowVision Flow Monitors are based on this method.

CTD-method (Constant Temperature Difference): Type FC01

The temperature difference between the two sensors is kept constant. The volume flow is determined by measuring the calorific power. This principle is mostly used by the Flow Meters.

Monitoring head installation for mass flow meters

For best performance heads monitoring liquid media should be installed in the pipeline in accordance with the following conditions:

  • In the case of vertical pipelines the monitoring head should be installed where the flow is rising, if possible.
  • For horizontal pipelines the monitoring head should be mounted on the underside of the line (suspended).
  • The monitoring head should be installed only in a straight section of piping. There should be a distance of at least 20 pipe diameters before the monitoring head and 5 pipe diameters after the monitoring head before or after any bends and changes in pipe diameter, to avoid the effects of any turbulence conditions that they may cause.
  • Avoid installing either the monitoring head or control unit in known areas of high electrical inductance, capacitance, or high-frequency electromagnetic fields.
  • The surface of the shaft end must not be recessed below the inner pipe wall. Preferably the shaft surface of the CST monitoring head should project approx. 1-2 mm towards the pipe centre.
  • If the medium to be monitored is a gas, the mounting attitude of the monitoring head in either vertical or horizontal pipelines is unimportant.

Monitoring head installation for mass flow monitors

For best performance heads monitoring liquid media should be installed in the pipeline in accordance with the following conditions:

  • In the case of vertical pipelines the monitoring head should be installed where the flow is rising, if possible.
  • For horizontal pipelines the monitoring head should be mounted on the underside of the line (suspended).
  • The monitoring head should be installed only in a straight section of piping. There should be a distance of at least 10 pipe diameters before the monitoring head and 5 pipe diameters after the monitoring head before or after any bends and changes in pipe diameter, to avoid the effects of any turbulence conditions that they may cause.
  • Avoid installing either the monitoring head or control unit in known areas of high electrical inductance, capacitance, or high-frequency electromagnetic fields.
  • The surface of the shaft end must not be recessed below the inner pipe wall. Preferably the shaft surface of the CST monitoring head should project approx. 1-2 mm towards the pipe centre.
  • If the medium to be monitored is a gas, the mounting attitude of the monitoring head in either vertical or horizontal pipelines is unimportant.
  • The flow direction to be observed with Flow Monitors with integral monitoring head (SFW 120-E, SLW 120-E) is marked on the housing.