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Publication Number: FHWA-HRT-12-072
Date: May 2013

 

Smart Pavement Monitoring System

APPENDIX A. DEVELOPMENT AND LABORATORY TESTING OF A PASSIVE TEMPERATURE GAUGE

The objective of this task is to show the feasibility of an on-chip passive temperature gauge that is able to transmit temperature data when interrogated. The gauge does not record temperature data continuously; it is only activated when a reader is within transmission range.

A.1 SENSOR DESIGN AND TESTING

The probe is based on the fact that the behavior of a transistor depends on temperature and employs an enhanced design of a proportional to absolute temperature current/voltage reference to output electrical variables (I, V) that are linearly related to temperature. The probe was translated to a schematic design, and a prototype was manufactured in a standard 0.02-mil (0.5-µ CMOS process and was tested. Figure 212 shows the implementation of the sensing probes. The obtained curves are used to calibrate the measurement probe. Figure 213 and figure 214 show the measured current and voltage from a tested prototype at temperatures varying from -4 to 122 °F (-20 to 50 °C). The response is clearly linear with respect to temperature, especially for voltage variations. The circuit in figure 212 is connected to the same wireless reading module discussed.

This illustration shows the circuit implementation of a temperature-dependent measuring system. It begins at a connector labeled V subscript dd!. It is connected in parallel with three P-type metal oxide semiconductors (PMOS), and each of these are in series with one PMOS. Connected in series with these are four N-type metal oxide semiconductors. There are two places where there are output nodes, labeled output current and output voltage. Within this circuit, there is a resistor labeled R, and at the bottom of the circuit, there is a connector labeled gnd!.
Figure 212 . Illustration. Circuit implementation of a temperature-dependent measuring system.

This graph shows variations of measured output current with respect to temperature. The x-axis shows the temperature, and the y-axis shows I subscript ref. The graph begins in the bottom right corner at 1.6 nA and -4 °F (-20 °C) and increases to 2.45 nA at 122 °F (50 °C).
°F = 1.8 °C + 32
Figure 213 . Graph. Variations of measured output current (figure 212) with respect to temperature.

This graph shows variations of measured output voltage with respect to temperature. The x-axis shows the temperature, and the y-axis shows V subscript ref. The graph begins in the upper left corner at 0.55 V at -4 °F (-20 °C) and decreases to just above 0.44 V at 122 °F (50 °C).
°F = 1.8 °C + 32
Figure 214 . Graph. Variations of measured output voltage with respect to temperature.

CMOS technology provides a means for integrating temperature and fatigue monitoring functionality on the same silicon substrate. A prototype was manufactured and tested, thus accomplishing the set objectives for this task. Although the temperature is not monitored continuously, the pavement temperature data can be collected during non-destructive testing (FWD/rolling wheel deflectometer) as part of a pavement management program.


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The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT). Provide leadership and technology for the delivery of long life pavements that meet our customers needs and are safe, cost effective, and can be effectively maintained. Federal Highway Administration's (FHWA) R&T Web site portal, which provides access to or information about the Agency’s R&T program, projects, partnerships, publications, and results.
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