Solartron Mobrey 7828, Техническое руководство

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Mechanical Installation 7828 Density Transmitter Technical Manual
2-14
78285000_AB
2.4 INSTALLATION IN THE PIPELINE OR SYSTEM
Density is a sensitive indicator of change in a fluid - a key reason why density
measurement is increasingly being chosen as a process measurement.
This means that measurements can be sensitive to extraneous effects and therefore
great care must be taken to consider all the factors which may affect measurement when
assessing the installation requirements.
Like many other transducers, the optimum performance of the density transmitter
depends upon certain conditions of the fluid and configuration of the process pipe-work.
By introducing appropriate flow conditioning, the optimum performance of the 7828 can be
achieved at any chosen location in the process system.
You must first select a location which serves the application objective; e.g. installed close
to the point of control. Then consideration can be given to fluid conditioning at that point.
Where the application requirements allow a degree of tolerance in the point chosen for
installation, the installation may be able take advantage of natural flow conditioning.
The choice of mechanical installation (free stream, “T” piece or flow-through chamber) will
be dictated partly by application needs and partly by the fluid conditions, such as:
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Condition of fluid at the sensor
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Thermal effects
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Flow rate
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Entrained gas
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Solids contamination
2.4.1 FLUID AT THE SENSOR
The fluid in the effective zone of the 7828 must be of uniform composition and at uniform
temperature. It must be representative of the fluid flow as a whole.
This is achieved either by mixing of the fluid either using a static inline mixer or taking
advantage of any natural pipe condition that tends to cause mixing, such as pump
discharge, partially open valves etc. The density transmitter should be installed
downstream.
2.4.2 THERMAL EFFECTS
For high viscosity fluids, temperature gradients in the fluid and in the pipe work and fittings
immediately upstream and downstream of the transmitter should be minimised in order to
reduce the effect of viscosity changes.
Always insulate the transmitter and surrounding pipework thoroughly. Insulation must be
at least 1”(25mm) of rockwool, preferably 2” (50mm) and enclosed in a sealed protective
casing to prevent moisture ingress, air circulation, and crushing of the insulation. Special
insulation jackets are available from Solartron for the flow-through chambers, which,
because of the low volumetric flow rates and hence low heat flow, are more vulnerable to
temperature effects.
Avoid direct heating or cooling of the transmitter and associated pipework upstream and
downstream that is likely to create temperature gradients. If it is necessary to provide
protection against cooling due to loss of flow, electrical trace heating may be applied,