78285000_AB 2-1
2
Mechanical Installation
2.1 INTRODUCTION
There are a variety of external factors which affect the ability of the 7828 to operate
successfully. In order to ensure that your system works correctly, the effects of these
factors must be taken into consideration when designing your installation.
There are two main aspects to consider:
1. The accuracy and repeatability of the measurements;
2. The relevance of the measurements to the overall purpose of the system.
Factors which may adversely affect accuracy and repeatability include:
•= The presence of gas or bubbles within the fluid being measured
•= Non-uniformity of the fluid
•= The presence of solids as contaminants
•= Fouling of the transducer
•= Temperature gradients
•= Cavitation and swirls caused by valves or discontinuities in the pipework
•= Operating at temperatures below the wax point of crude oils
•= The measured fluid being unrepresentative of the main flow.
In some applications, absolute accuracy is less important than repeatability. For example,
in a system where the control parameters are initially adjusted for optimum performance,
and thereafter only checked periodically.
The term achievable accuracy can be used to describe a measure of the product quality
that can be realistically obtained from a process system. It is a function of measurement
accuracy, stability and system response. High accuracy alone is no guarantee of good
product quality if the response time of the system is measured in tens of minutes, or if the
measurement bears little relevance to the operation of the system. Similarly, systems
which require constant calibration and maintenance cannot achieve good achievable
accuracy.
Factors which may adversely affect the relevance of the measurements could include:
•= Measurement used for control purposes being made too far away from the point of
control, so that the system cannot respond properly to changes;
•= Measurements made on fluid which is unrepresentative of the main flow.
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