Method and apparatus for measuring the density of fluids

• US 4,956,793 A
• Filed: 06/24/1988
• Issued: 09/11/1990
• Est. Priority Date: 06/24/1988
• Status: Expired due to Fees

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Bonne, Ulrich, James, Steven D.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Mattson, Brian M.
• Application Number:
  US07/211,014
• Time in Patent Office: 809 Days
• Field of Search: 364/509, 364/554, 364/558, 73/23, 73/26, 73/27 R, 73/30, 73/32 R, 374/14, 374/43, 374/44, 374/45
• US Class Current: 702/50
• CPC Class Codes: G01N 25/18 by investigating thermal conductivity by calorimetry G01N25/20; by measuring change of resistance of an electrically-heated body G01N27/18
• CPC Class Codes: G01N 9/04 of fluids

Abstract

The specific gravity, l, of a fluid of interest is determined based on thermal conductivity, k, and specific heat, c_p, of the fluid of interest. An embodiment uses proximately positioned resistive heater and thermal sensor elements coupled by the fluid of interest. Pulses of electrical energy are applied to the heater of a level and duration such that both a transient change and a substantially steady-state temperature occur in the sensor. The k of the fluid of interest is determined based upon sensor output at steady-state elevated temperature, c_p of the fluid of interest is determined based upon the rate of change of sensor output during a time interval of transient temperature change in the sensor, and l is determined from k and c_p.

Claims

1. Apparatus for determining specific gravity, ρ

, of a fluid of interest comprising;

electrical resistance heater means;

thermal sensor means in proximate position to said heater means and in thermal communication therewith through the fluid of interest, the thermal sensor means having an output dependent on thermal sensor temperature;

adjustable electrical energizing means connected to said heater means for energizing said heater means on a time and level-variable pulse basis in a manner to induce both transient and substantially steady-state elevated temperature condition intervals in said thermal sensor means;

means for adjusting level and duration of the output of the adjustable electrical energizing means;

first output means for providing a first output signal indicative of a temperature of said thermal sensor means;

timing means for determining a rate of change of temperature of said temperature sensor during a transient temperature interval based on time variation of said first output signal between at least two known values;

means for determining k of the fluid of interest based upon said first output signal at steady-state elevated sensor temperature; and

means for determining c_p, of the fluid of interest based on k and the rate of change of the first output signal during a transient temperature condition;

means for producing signals indicative of the values of k and c_p of the fluid of interest;

conversion means for converting signals indicative of the values of k and c_p of the fluid of interest to values indicative of ρ

of the fluid of interest.

2. The apparatus of claim 1 further comprising second output means for providing output signals indicative of ρ

of the fluid of interest.

3. The apparatus of claim 1 wherein said timing means further comprises counting means for measuring a time interval required for said first output signal to rise or fall between at least two known values, and means to adjust said at least two known values.

4. The apparatus of claim 1 wherein said resistive sensor is part of a Wheatstone bridge and said first output signal is a voltage signal.

5. Apparatus for determining specific gravity, ρ

, of a fluid of interest comprising;

a microbridge system including a thin film resistive heater and a thin film resistive sensor in juxtaposed spaced relation, said thin film resistive heater and said thin film resistive sensor each having terminals, said microbridge system further being positioned in direct communication with the fluid of interest, said thin film resistive heater thereby being thermally coupled to said thin film resistive sensor via said fluid of interest;

electrical pulse producing means connected in energizing relation to terminals connected to the tin film resistive heater for providing a voltage input pulse to the thin film resistive heater of a variable level and duration such that variable intervals of transient temperature conditions, having characteristic rates of change, and variable levels of substantially steady-state elevated temperature conditions are capable of being induced in the thin film resistive sensor via the fluid of interest;

means for varying the variable level and duration of each said voltage input pulse;

first output means for providing a first electrical potential output signal indicative of a temperature of said thin film resistive sensor;

timing means for determining a rate of change of temperature of said thin film resistive sensor during a transient temperature interval based on a time interval between selected first electrical output signals indicated by said first output means;

means for producing signals indicative of k of the fluid of interest based upon selected first electrical output signals indicated by said first output means at a steady-state elevated thin film sensor temperature;

means for producing signals indicative of c_p of the fluid of interest based on k and a rate of change of a first electrical potential output signal during a transient temperature interval;

means for producing signals indicative of values of k and c_p of the fluid of interest; and

conversion means for converting signals related to values of k and c_p of the fluid of interest to signals indicative of ρ

of the fluid of interest.

6. The apparatus of claim 5 further comprising second output means for providing output signals indicative of ρ

of the fluid of interest.

7. The apparatus of claim 5 wherein said thin film resistive heater and thin film resistive sensor are the same thin film resistor.

8. The apparatus of claim 5 wherein said thin film resistive heater and thin film resistive sensor comprise a sensor-heater-gap-heater-sensor configuration.

9. The apparatus of claim 5 wherein said thin film resistive heater and thin film resistive sensor comprise a heater-gap-sensor configuration.

10. The apparatus of claim 5 wherein said thin film resistive heater and thin film resistive sensor means are provided with an outer insulating layer to reduce heat flow through solid media.

11. The apparatus of claim 5 wherein said timing means further comprises counting means for measuring said time interval required for said first electric output signal to rise or fall between at least two known values, and means to adjust said at least two known values.

12. The apparatus of claim 5 wherein said thin film resistive sensor is part of a Wheatstone bridge.

13. A method of determining specific gravity, ρ

, of a fluid of interest comprising the steps of;

providing a heater means and a thermal sensor means proximately positioned and coupled by said fluid of interest, said thermal sensor means having a temperature sensitive output;

providing at least one energy input pulse to the heater means of a level such that an interval of transient temperature change is correspondingly produced in the thermal sensor means;

providing at least one energy input pulse to the heater means of a duration such that an interval of substantially steady-state elevated temperature is correspondingly produced in the thermal sensor means;

obtaining a sensor output related to the elevated temperature of the thermal sensor means at said steady-state temperature;

determining k of the fluid of interest based upon sensor output at said steady-state elevated sensor temperature;

determining the rate of change of sensor output during a portion of said transient temperature change in the sensor; and

determining c_p of the fluid of interest based upon a rate of change of sensor output during an interval of transient temperature change and k; and

determining ρ

of the fluid of interest as a function of c_p and k.

14. The method of claim 13 including the step of determining k at a plurality of steady-state temperatures.

15. The method of claim 14 wherein the specific gravity ρ

, of the fluid of interest is determined according to a function of c_p and k;

space="preserve" listing-type="equation">ρ

=a.sub.6 +a.sub.7 c.sub.pt.sbsb.7.sup.n.sbsp.7 + . . . +a.sub.8 k.sub.t.sbsb.8.sup.n.sbsp.8 + . . . +a.sub.m k.sub.t.sbsb.m

where;

a₆ -a_m are constants

k_t.sbsb.1 -k_t.sbsb. are thermal conductivities at different temperatures and

n₁ -n_m are exponents.

16. The method of claim 13 including the step of determining k and c_p at a plurality of temperatures.

17. The method of claim 13 wherein said fluid of interest is a gas.

18. A method for determining specific gravity, ρ

, of a fluid of interest comprising the steps of;

providing proximately positioned microbridge thin film electrical resistance heater and thermal sensor means coupled by said fluid of interest, said thermal sensor means having a temperature sensitive electrical output signal;

providing an electrical energy input pulse to the resistance heater means of a level such that the thermal sensor means experiences an interval of transient temperature change and of a duration such that the thermal sensor means experiences an interval of substantially steady-state elevated temperature;

obtaining an electrical sensor output related to the thermal sensor temperature at a steady-state elevated temperature;

determining k of the fluid of interest based upon an electrical sensor output signal at said steady-state elevated sensor temperature;

obtaining an output related to a rate of change of temperature of the thermal sensor during a transient temperature change;

determining c_p of the fluid of interest based on a rate of change of sensor output during a transient temperature change in said thermal sensor and k; and

determining ρ

of the fluid of interest as a function of c_p and k.

19. The method of claim 18 including the step of determining k at a plurality of steady-state temperatures.

20. The method of claim 19 wherein the specific gravity, ρ

, of the fluid of interest is determined as a function of c_p and k;

space="preserve" listing-type="equation">ρ

=a.sub.6 +a.sub.7 c.sub.pt.sbsb.7.sup.n.sbsp.7 + . . . +a.sub.8 k.sub.t.sbsb.8.sup.n.sbsp.8 + . . . +a.sub.m k.sub.t.sbsb.m

where;

a₆ -a_m are constants

k_t.sbsb.1 -k_t.sbsb.m are thermal conductivities at different temperatures; and

n₁ -n_m are exponents.

21. The method of claim 18 including the step of determining k and c_p at a plurality of temperatures.

22. The method of claim 21 wherein the specific gravity, ρ

, of the fluid of interest is determined according to the function of c_p and k;

space="preserve" listing-type="equation">ρ

=a.sub.6 +a.sub.7 c.sub.pt.sbsb.7.sup.n.sbsp.7 + . . . +a.sub.8 k.sub.t.sbsb.8.sup.n.sbsp.8 + . . . +a.sub.m k.sub.t.sbsb.m.sup.n.sbsp.m

where;

a₆ -a_m are constants

k_t.sbsb.1 -k_t.sbsb.m are thermal conductivities at different temperatures; and

n₁ -n_m are exponents.

23. The method of claim 18 wherein said fluid of interest is a gas.

24. A method for determining specific gravity, ρ

, of a gas of interest comprising the steps of;

providing proximately positioned thin film microbridge electrical elements including a resistive heater and a resistive sensor coupled by said fluid of interest, said resistive sensor having a temperature sensitive sensor output signal;

providing at least one electrical energy input pulse to the resistive heater means of a known level and of a known duration such that the resistive sensor means achieves at least one interval of substantially steady-state elevated temperature;

obtaining at least one sensor output signal related to sensor temperature at an elevated steady-state temperature; and

determining k of the fluid of interest based upon thermal sensor output at least one steady-state elevated sensor temperature substantially approximated by;

space="preserve" listing-type="equation">k=a.sub.4 U+a.sub.5

where U is the sensor output and a₄ and a₅ are constants;

obtaining an output indicative of a rate of change of temperature of the thermal sensor means by measuring time interval for thermal sensor temperature to change between two known temperatures;

determining c_p of the gas of interest based on the relation;

space="preserve" listing-type="equation">c.sub.p P/P.sub.o =a.sub.1 (t.sub.2 -t.sub.1)k+a.sub.2 (t.sub.2 -t.sub.1)-a.sub.3

where;

a₁, a₂ and a₃ are constants

p=pressure (psia)

P_o =reference pressure (psia)

(t₂ -t₁)=measured time span for the temperature of the thermal sensor means to change between known temperatures; and

determining ρ

of the gas of interest as a function c_p and k;

space="preserve" listing-type="equation">ρ

=a.sub.6 +a.sub.7 c.sub.pt.sbsb.7.sup.n.sbsp.7 + . . . +a.sub.8 k.sub.t.sbsb.8.sup.n.sbsp.8 + . . . +a.sub.m k.sub.t.sbsb.m

where;

a₆ -a_m are constants

k_t.sbsb.1 -k_t.sbsb.m are thermal conductivities at different temperatures and

n₁ -n_m are exponents.

25. The method of claim 24 including the step of determining k at a plurality of steady-state temperatures.