Thermal type of flow rate sensor
AssigneeNGK Insulators, Ltd.
InventorYasuhito Yajima
Life of this patent
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Abstract
A thermal type of flow rate sensor includes heat-generating and temperature-compensating resistors R.sub.H and R.sub.C which are located within a fluid passage to measure the flow rate of the fluid. The linear term coefficient, .alpha., of the temperature coefficient of resistance of R.sub.C is made smaller than that of R.sub.H, whereby any temperature-compensating electric circuit and circuit control can all be dispensed with and the flow rate of a fluid can be precisely detected over a wide temperature range.
Claims2
In a thermal flow rate sensor having a heat-generating resistor and a temperature-compensating resistor both positioned within a fluid passage and used in sensing flow rate of a fluid in the passage, the improvement comprising:
- a platinum heat-generating resistor R.sub.H for detecting the flow rate of the fluid within the passage;
- and
- a platinum temperature-compensating resistor R.sub.C coupled to said platinum heat-generating resistor R.sub.H in contact with the fluid in the passage;
- wherein the resistance value r.sub.H (.OMEGA.), of said platinum heat-generating resistor R.sub.H is given by the following function of temperature of fluid in the passage, T(.degree.C.):
- r.sub.H =r.sub.HO (1+.alpha..sub.H T+.beta..sub.H T.sup.2),
- wherein r.sub.HO (.OMEGA.) is the resistance value at 0.degree. C. of said platinum heat-generating resistor R.sub.H, .beta..sub.H is a second-order term coefficient, and .alpha..sub.H is a linear first-order term coefficient of a temperature coefficient of resistance of said platinum heat-generating resistor R.sub.H ;
- and
- wherein the resistance value, r.sub.C (.OMEGA.), of said platinum temperature-compensating resistor R.sub.C is given by the following function of temperature of fluid in the passage, T(.degree.C.):
- r.sub.C =r.sub.CO (1+.alpha..sub.C T+.beta..sub.C T.sup.2).
- wherein r.sub.CO (.OMEGA.) is the resistance value at 0.degree. C. of said platinum temperature-compensating resistor R.sub.C, .beta..sub.C is a second-order term coefficient, and .alpha..sub.C is a value of the linear first-order term coefficient of a temperature coefficient of resistance of said platinum temperature-compensating resistor R.sub.C, and wherein the value of the linear first-order term coefficient, .alpha..sub.C, of the temperature coefficient of resistance of said platinum temperature-compensating resistor R.sub.C is smaller than the linear first-order term coefficient, .alpha..sub.H, of the temperature coefficient of resistance of said platinum heat-generating resistor R.sub.H by 100 ppm/.degree.C. to 250 ppm/.degree.C.
Dependencies are inferred from the claim text.