Flow measurement system

In a system having first flow rate transducers for measuring a rate of flow of a first fluid in a first part of said system and having second flow rate transducers for measuring a rate of flow of a second fluid flow combined with said first fluid flow in a second part of said system, a subsystem for measuring said rate of flow of said second fluid from a rate of flow measurement of said first fluid prior to such combination of said fluid flows and a rate of flow measurement of said first fluid in combination with said second fluid, said system having a calibration period and an operational period, comprising:

• a first flow rate transducer, having an inherent inaccuracy, for producing a first electrical signal proportional within a first inherent error to a rate of flow of said first fluid therethrough;
• a second flow rate transducer, having an inherent inaccuracy, connected in series with said first flow rate transducer for producing a second electrical signal proportional within a second inherent error to said rate of flow of said first fluid therethrough;
• a third flow rate transducer, having an inherent inaccuracy, connected to receive said combined flow of said first and second fluids for producing a third electrical signal proportional within a third inherent error to a rate of flow of said combined flow of said first and second fluids;
• a fourth flow rate transducer, having an inherent inaccuracy, connected in series with said third transducer for producing a fourth electrical signal proportional within a fourth inherent error to said rate of flow of said combined flow of said first and second fluids;
• means for temporarily causing said first fluid only to flow through said third and fourth transducers during said calibration period of said system and for causing said combined fluids to flow through said third and fourth transducers during said operational period of said system;
• a computer connected to said first, second, third, and fourth flow rate transducers for receiving said first, second, third, and fourth electrical signals;
• program means resident in said computer, said program means including a calibration algorithm for calculating first scale factors from a difference between said signals from said first, and second transducers during said calibration period of said system, said first scale factors applied to said first and second signals during said operational period of said system for correcting for the difference therebetween, said calibration algorithm for calculating second scale factors from a difference between said signals from said third and fourth transducers during said calibration period of said system, said second scale factors applied to said third and fourth signals during said operational period of said system for correcting for the difference therebetween;
• and
• said program means including a monitoring algorithm for monitoring said difference between said first and second electrical signals, and said difference between said third and fourth electrical signals during said operational period and for indicating a fault when at least one of said differences varies from the corresponding difference measured during said calibration period.

A method of monitoring and calibrating a pair of tandem connected electrical transducers for measuring a rate of flow of a fluid through a system, the pair of transducers connected to a computer, the computer for receiving electrical signals from the transducers essentially proportional to the rate of flow of the fluid therethrough, comprising the steps of:

• (a) producing a constant rate of flow of the fluid through each of the pair of transducers;
• (b) initiating a calibration phase of the system;
• (c) recording a set of samples of the fluid flow rate signals in the computer;
• (d) calculating an average fluid flow rate signal level from each set of samples;
• (e) comparing an average of each of the set of samples and calculating a scale factor to produce equal flow measurement values from each transducer;
• (f) initiating an operational phase of the system;
• (g) comparing calculated flow measurement values from each transducer during the operational phase;
• and
• (h) initiating a fault indication when such compared calculated values differ from each other by a preselected percentage.