Roadway freezing point monitoring system and method

• US 20050058177A1
• Filed: 11/05/2003
• Published: 03/17/2005
• Est. Priority Date: 11/19/2001
• Status: Active Grant

• Current Assignee: Kroneis GmbH
• Original Assignee: Energy Absorption Systems, Inc. (Trinity Industries Incorporated)
• Inventors: Leonhardt, Patrick A.
• Granted Patent: US 7,090,392 B2
• Time in Patent Office: Days
• US Class Current: 374/16
• CPC Class Codes: G01N 27/04 by investigating resistance
• CPC Class Codes: G08B 19/02 Alarm responsive to formation or anticipated formation of ice

Abstract

Improved roadway freezing point monitoring systems and methods include improved sample wells for the accurate measurement of the freezing point of liquid on a roadway, the use of temperature sensors that require only two conductors to receive power and to send and receive digital address and temperature information, improved algorithms for detecting the freeze point of liquid on the roadway, the use of conductivity measurements to verify detected freeze points, and the transmission of temperature information via the Internet to remote computers.

Claims

1. A roadway freezing point sensor comprising:

a sensor module configured to be embedded in a roadway, said sensor module comprising an active cooler, a cold thermal link in thermal contact with the active cooler, a sample well adjacent the thermal link, and a temperature sensor adjacent the sample well;

said sample well comprising a first surface in good thermal contact with the temperature sensor and a second surface in good thermal contact with the thermal link;

said thermal link having a thermal conductivity greater than 1 W/m·

K closely adjacent the second surface of the sample well.

2. The invention of claim 1 wherein the thermal link extends completely around the sample well.

3. The invention of claim 1 further comprising:

a thermally insulating cover disposed over a portion of the cold thermal link spaced from the sample well.

4. The invention of claim 3 wherein the cover defines an opening positioned above the sample well.

5. The invention of claim 4 wherein the sample well projects an area A1 in a horizontal plane, wherein the opening in the cover projects an area A2 in the horizontal plane, and wherein A2>

A1.

6. The invention of claim 5 wherein the opening forms a sample cup having a lower surface in good thermal contact with the cold thermal link.

7. The invention of claim 6 further comprising a pair of conductivity probes in good electrical contact with a measurement zone bounded by the sample cup, said conductivity probes positioned alongside the temperature sensor.

8. The invention of claim 7 wherein the sample cup comprises a surface formed by the cover.

9. The invention of claim 1 further comprising a thermally insulating element positioned between the temperature sensor and the cold thermal link.

10. The invention of claim 1 wherein the thermal link has a thermal conductivity greater than 5 W/m·

K closely adjacent the second surface of the sample well.

11. The invention of claim 1 wherein the thermal link has a thermal conductivity greater than 20 W/m·

K closely adjacent the second surface of the sample well.

12. The invention of claim 1 wherein the thermal link has a thermal conductivity greater than 100 W/m·

K closely adjacent the second surface of the sample well.

13. A roadway temperature monitoring system comprising:

a base station;

a plurality of sensor modules embedded in a roadway, each sensor module comprising a digital temperature sensor having a respective address which is globally unique within the temperature monitoring system;

a set of cables interconnecting the base station with the sensor modules, said cables comprising no more than two conductors connected to each sensor module;

said sensor modules each comprising a respective power circuit operative to draw operating power for the respective sensor module from the conductors;

said sensor modules operative to transmit temperature information and address information to the base station as serial digital signals via the conductors.

14. A method for measuring a liquid freezing point on a roadway, said method comprising:

(a) providing a sensor module embedded in a roadway, said sensor module comprising a measurement zone on an upper surface thereof, a temperature sensor in good thermal contact with the measurement zone, a pair of conductivity probes in good electrical contact with the measurement zone, and an active cooler thermally coupled to the measurement zone;

(b) progressively cooling the measurement zone with the active cooler;

(c) recording temperature measurements of the measurement zone with the temperature sensor repeatedly during (b);

(d) recording conductivity measurements of the measurement zone with the conductivity probes repeatedly during (b);

(e) determining a freezing point of a liquid in the measuring zone based on both variations in time of the temperature measurements of (c) and the conductivity measurements of (d).

15. The method of claim 14 wherein (e) comprises:

(e1) determining the freezing point based on variations in time of the temperature measurements of (c); and

(e2) checking whether the conductivity measurements of (d) indicate a substantial decrease in conductivity substantially coincident with the freezing point determined in (e1).

16. The method of claim 14 wherein the measurement zone of (a) comprises a sample well having a first surface in good thermal contact with the temperature sensor and a second surface in good thermal contact with the active cooler.

17. The method of claim 15 wherein (e1) comprises:

(e1a) determining a second time derivative of the temperature measurements of (c);

(e1b) comparing the second time derivative of (e1a) with a positive threshold value; and

(e1c) determining the freezing point based on detection of a leveling off of the temperature measurements of (c) after the second time derivative of (e1 a) has exceeded the threshold value of (e1b).

18. A method for measuring a liquid freezing point on a roadway, said method comprising:

(a) providing a sensor module embedded in a roadway, said sensor module comprising a measurement zone on an upper surface thereof, a temperature sensor in good thermal contact with the measurement zone, and an active cooler thermally coupled to the measurement zone;

(b) progressively cooling the measurement zone with the active cooler;

(c) recording temperature measurements of the measurement zone with the temperature sensor repeatedly during (b);

(d) determining a second time derivative of the temperature measurements of (c);

(e) determining when the second time derivative of (d) exceeds a positive threshold value; and

(f) determining the freezing point based at least in part on a leveling off of the temperature measurements of (c) after the second time derivative of (d) has exceeded the threshold value of (e).

19. The method of claim 18 wherein (d) comprises:

(d1) determining a plurality of first slopes of the temperature measurements of (c) versus time, each first slope associated with a respective measurement time; and

(d2) determining a plurality of second slopes of the first slopes of (d1) versus time.

20. A method for measuring a liquid freezing point on a roadway, said method comprising:

(a) providing a sensor module embedded in a roadway, said sensor module comprising a measurement zone on an upper surface thereof, a temperature sensor in good thermal contact with the measurement zone, and an active cooler thermally coupled to the measurement zone;

(b) progressively cooling the measurement zone with the active cooler;

(c) recording temperature measurements of the measurement zone with the temperature sensor repeatedly during (b);

(d) determining a first time derivative of the temperature measurements of (c);

(e) determining when the first time derivative rises above a first, positive threshold value; and

then

(f) determining when the first time derivative falls to within a range of values bounded above by zero and below by a second, negative threshold value.

21. The method of claim 20 wherein (d) comprises:

(d1) fitting a plurality of lines to the temperature measurements of (c); and

(d2) determining a first time derivative of the lines of (d1).

22. The method of claim 21 further comprising:

(g) associating the earliest temperature measurement included in the line associated with a time determined in (f) as the liquid freezing point.

23. A roadway monitoring system comprising:

a base station;

a plurality of sensor modules embedded in a roadway and coupled with the base station, each sensor module comprising a temperature sensor and a memory storing an address which is globally unique within the monitoring system;

means for transmitting temperature information from the sensor modules to the base station; and

means for transmitting temperature information from the base station via a network to a remote computer.

24. The invention of claim 23 wherein the network comprises the Internet.