Measuring and control of low fluid flow rates with heated conduit walls

A system for controlling the flow of fluid at a measured rate of flow, comprising:

• a flow sensing assembly, comprising:
• a conduit having walls for containing and transporting the fluid;
• at least two heat detectors mounted at spaced positions from each other on the conduit walls and measuring the temperature of the fluid and conduit at the spaced positions;
• at least two electrical power applicators mounted on the conduit and allowing electrical current to flow in the conduit walls to heat the fluid in the conduit at and maintain an established temperature differential;
• a housing body having the flow sensing assembly contained therein;
• a control mechanism for obtaining measurements of the amount of energy furnished to the heat applicators to the established temperature differential between the spaced positions;
• an indicator mechanism responsive to the control mechanism providing a measure of the fluid flow rate based on the measurements obtained by the control mechanism;
• and
• a flow regulating valve responsive to the measure of the fluid flow rate to control the flow of fluid in the conduit.

A system for measuring the flow of fluid in a conduit, comprising:

• at least two heat detectors mounted at spaced positions from each other on the conduit measuring the temperature of the fluid and conduit at the spaced positions;
• an amplifier forming a measure of difference in temperature sensed by the heat detectors;
• a comparator forming a signal representative of the variation of the temperature difference measured by the heat detectors from an established temperature differential;
• at least two electrical power applicators mounted at different locations on the conduit and allowing electrical current to flow in the conduit walls to heat the fluid in the conduit and maintain an established temperature differential between the spaced positions;
• a control mechanism for obtaining measurements of the level of electrical power furnished to the power applicators to maintain the established temperature differential between the spaced positions;
• and
• an indicator mechanism responsive to the control mechanism providing a measure of the fluid flow rate based on the measurements obtained by the control mechanism.