Time lag approach for measuring fluid velocity

Apparatus for determining the fluid velocity, v, of a fluid of interest, comprising:

• heater means in thermal communication with the fluid of interest, said heater means having a resistance that changes with temperature;
• heater energizing means connected to said heater means for energizing said heater means, said heater energizing means providing a heater input signal to said heater means to provide a transient elevated temperature condition in said heater means;
• first sensor means in thermal communication with the fluid of interest, said first sensor means spaced a first distance from said heater means and having a resistance that changes with temperature;
• second sensor means in thermal communication with the fluid of interest, said second sensor means spaced a second distance from said heater means wherein said second distance is different from said first distance, and having a resistance that changes with temperature;
• first sensor energizing means connected to said first sensor means for providing a first sensor input signal to said first sensor means;
• second sensor energizing means connected to said second sensor means for providing a second sensor input signal to said second sensor means;
• first sensor time lag means for determining a first sensor time lag between the first sensor input signal and the resulting resistance change of said first sensor means;
• second sensor time lag means for determining a second sensor time lag between the second sensor input signal and the resulting resistance change of said second sensor means;
• said first input power signal being out of phase relative to the input signal provided by said heater energizing means by a sufficient amount to cause said first sensor time lag to be substantially equivalent to a first predetermined time value;
• said second input power signal being out of phase relative to the input signal provided by said heater energizing means by a sufficient amount to cause said second sensor time lag to be substantially equivalent to a second predetermined time value;
• output time lag means for determining a first output time lag, Δz1, between the heater and the first sensor, and a second output time lag, Δz2, between the heater and the second sensor;
• and
• determining means for determining the fluid velocity, v, of the fluid of interest using the relation:
• v={(d12/Δz1−d22Δz2)/(Δz1−Δz2)}0.5
• where,
• d1=the distance between the heater means and a first sensor means;
• d2=the distance between the heater means and the second sensor means, where |d1|≠|d2|.

A method for determining the fluid velocity, v, of a fluid of interest using a heater element and at least two spaced sensor elements, the method comprising the steps of:

• providing a first one of the sensor elements a first distance from the heater element, and a second one of the sensor elements a second distance from the heater element, wherein the second distance is greater than the first distance;
• energizing said heater element to providing a transient elevated temperature condition in said heater element;
• determining a first time lag value between the heater element and the first one of the sensor elements;
• determining a second time lag value between the heater element and the second one of said sensor elements;
• determining the fluid velocity, v, of the fluid of interest using the first and second time lag values.

A method for measuring the velocity of a fluid of interest using a heater element and a number of spaced sensor elements, the method comprising the steps of:

• providing a first one of the sensor elements a first distance from the heater element, and a second one of the sensor elements a second distance from the heater element, wherein the first distance is greater than the second distance;
• providing a time-varying heater input signal to said heater element to provide a transient elevated temperature condition in said heater element;
• providing a first sensor input signal to said first sensor element;
• providing a second sensor input signal to said second sensor element;
• determining a first sensor time lag between the first sensor input signal and the resulting resistance change of said first sensor element;
• determining a second sensor time lag between the second sensor input signal and the resulting resistance change of said second sensor element;
• changing the phase of the first sensor input signal relative to the heater input signal by a sufficient amount to cause said first sensor time lag to be substantially equivalent to a first predetermined time value.
• changing the phase of the second sensor input signal relative to the heater input signal by a sufficient amount to cause said second sensor time lag to be substantially equivalent to a second predetermined time value.
• determining a first output time lag, Δz1, by determining the lag between the heater and the first sensor;
• determining a second output time lag, Δz2, by determining the lag between the heater and the second sensor;
• determining the fluid velocity, v, of the fluid of interest using the relation:
• v={(d12/Δz1−d22Δz2)/(Δz1−Δz2)}0.5
• where,
• d1=the distance between the heater element and a first sensor element;
• d2=the distance between the heater element and the second sensor element, where |d1|≠|d2|.

A method for determining a time lag between a transient elevated temperature condition of a heater element and the transient elevated temperature response of a sensor element through a fluid of interest, the method comprising the steps of:

• energizing the heater element to providing a transient elevated temperature condition in said heater element and thus the fluid of interest;
• energizing the sensor element with a sensor input signal, wherein said sensor input signal has a phase and an amplitude that causes substantially no heat to be transferred from the fluid of interest to the sensor element during the transient elevated temperature condition;
• and
• measuring the time lag between said heater element and the sensor element.

Apparatus for determining a time lag between a first location and a second location for a transient elevated temperature condition in a fluid, comprising:

• energizing means for energizing a heater element that is thermally coupled to the fluid, thereby providing the transient elevated temperature condition in the fluid;
• first optical means for optically detecting the transient elevated temperature condition at a first location;
• second optical means for optically detecting the transient elevated temperature condition at a second location, wherein the second location is spaced from the first location;
• and
• determining means for determining the time lag between the detected temperature response at the first location and the detected temperature response at the second location.

A method for determining a time lag between a first location and a second location for a transient elevated temperature condition in a fluid, comprising the steps of:

• energizing a heater element that is thermally coupled to the fluid, thereby providing the transient elevated temperature condition in the fluid;
• optically detecting the transient elevated temperature condition at a first location using a first optical device;
• optically detecting the transient elevated temperature condition at a second location using a second optical device, wherein the second location is spaced from the first location;
• and
• determining the time lag between the detected temperature response at the first location and the detected temperature response at the second location.