Patent RU-2761932-C1 (RU)
Title: Method for measuring the flow rate of a fluid medium and apparatus for implementation thereof
Inventor: GONCHAR IGOR IVANOVICH
IPC: G01F1/68
Filed: 2020-10-26
Granted: 2021-12-14
Abstract: FIELD: measuring equipment. 
     SUBSTANCE: invention relates to measuring equipment and can be used to determine the flow rate of liquids and gases at the control point of a pipeline section using a thin-film thermistor. The method for measuring the flow rate of a fluid medium consists in heating the thermistor with a pulsed current followed by determining the flow rate of the fluid medium by measuring the resistance thereof, wherein measurement of the flow rate of the fluid medium by the thermoanemometric method by measuring the resistance of the thermistor at the moment of application of the heating pulses and after application thereof and by the calorimetric method by measuring the difference between the resistance of the thermistor at the moment of application of the pulses prior to and after heating the thermistor is used simultaneously. For this purpose, a cyclic alternate connection of the current source to the thermistor is used for heating thereof with a flowing current greater than 10 mA, providing a heating temperature greater than 50° relative to the temperature of the fluid medium and the current source for measuring the value of resistance less than 1 mA, reducing the self-heating of the thermistor to the minimum. The resistance of the thermistor is measured at different points of time at different temperatures, in a cold state prior to application of the heating pulse, in the hot state at the end of the heating pulse and at the point of cooling after application of the heating pulse. The value of resistance depends on the flow rate and temperature of the medium at the moments of heating and cooling, and in the cold state, prior to application of the heating pulse, the value of resistance only depends only on the temperature of the fluid medium and is used to measure the temperature of the fluid medium. The thermoanemometric method for measuring the flow rate, accounting for the influence of the temperature of the fluid medium, is therein used to determine the flow rate by determining the flow rate by the change in the resistances in the hot state or at the moment of cooling, and the temperature of the fluid medium is determined by the change in the resistance in the cold state prior to application of the heating pulse, and a correction is introduced to account for the influence of the temperature of the fluid medium, changing the measured resistances used to measure the flow rate. The calorimetric method for measuring the flow rate using a single thermistor heated by current pulses is also used by determining the flow rate by the change in the difference of the resistances at the points in time prior to and after application of the heating pulses, regardless of the temperature of the medium, since the temperature of the medium does not change at the time of measurement. The apparatus for measuring the flow rate of a fluid medium comprises a measuring apparatus (1) and a thermoresistive sensor (2) consisting of a body (3) screwed by one side thereof on a branch pipe tee (4), located in the centre whereof along the flow axis is a free end face of a printed circuit board (5) with a thermistor (6) - R Q  spot-welded in a cantilever manner. The end opposite to the free end of the printed circuit board (5) (the second end thereof) is cantilevered in the body (3). An electrical connector (7) is hermetically installed on the other side of the body (4) opposite to the threaded section thereof, contacts (8) whereof are connected with the conductors of the printed circuit board (5) - the contact pads of the printed conductors - by wires. The electrical connector (7) of the thermoresistive sensor (2) is connected by a cable to the measuring apparatus (2) containing a circuit with analogue-to-digital converters, a microcontroller (MC) with software control and an output to the recorder in the form of a personal computer. A thin-film platinum thermistor on a glass substrate is applied in the measuring apparatus (1) as a spot-welded thermistor R Q , made with the meander area sizes of the resistor thereof of no more than 1 mm 2  and placed on a thin insulating substrate with a width of no more than 1 mm and a thickness of no greater than 200 mcm with a low thermal retention with the thermal inertia indicator of no more than 5 ms. The measurement results are processed in the measuring apparatus (1) using at least 16-bit analogue-to-digital converters and an MC with software control intended to control the modes of current supply and measurement of the values of resistance and digital filtering thereof, and the formation of a digital sequence for transmitting the measurement results from the output of the measuring apparatus to the input of the recorder, e.g., a PC, for further processing and imaging of the measurement results. The electrical connector (7) can be made sealed and installed on the body through a sealing plate (9). The space of the body (3) with wires between the electrical connector (7) in a basic implementation with contacts (8) and the fixed end of the printed circuit board (5) with the thermistor R Q  (6) can be filled with a hardened compound (10). A similar additional thermistor Rt (11) can be installed in the thermoresistive sensor (2) on the reverse side of the printed circuit board (5) thereof along the free end opposite the thermistor (6) welded in a cantilever manner - the main spot-welded thermistor R Q  (6). The thermistor Rt (11) is connected by the wires thereof with the contacts (8) of the electrical connector (7) of the thermoresistive sensor (2). 
     EFFECT: increase in the accuracy of measurements, an extension in the range of measurement of the flow rate of the fluid medium by the thermistor, as well as an increase in the reliability of the thermistor due to elimination of overheating thereof. 
     5 cl, 12 dwg