Hotbox detector

• US 4,068,811 A
• Filed: 04/28/1977
• Issued: 01/17/1978
• Est. Priority Date: 04/28/1977
• Status: Expired due to Term

• Current Assignee: Harmon Industries, Inc. (GE Aerospace)
• Original Assignee: General Electric Company
• Inventors: Caulier, Paul W.
• Primary Examiner(s): Blix, Trygve M.
• Assistant Examiner(s): Eisenzopf, Reinhard J.
• Application Number:
  US05/791,955
• Time in Patent Office: 264 Days
• Field of Search: 246/169 A, 246/169 D, 246/DIG. 1, 246/DIG. 2, 116/101, 116/114.5, 116/DIG. 38, 340/227 R, 340/228 R, 340/231, 340/269, 250/338, 250/339, 250/340, 73/355 R
• US Class Current: 246/169.00A
• CPC Class Codes: B61K 9/06 by detecting or indicating heat radiation from overheated axles
• CPC Class Codes: G01J 5/34 using capacitors, e.g. pyroelectric capacitors
• CPC Class Codes: Y10S 116/38 Hot box alarm
• CPC Class Codes: Y10S 246/02 Thermal sensing devices

Abstract

An apparatus for determining the temperature of railroad car wheel journals (i.e., "hotbox" detector) includes a sensor including a pyroelectric cell responsive to infrared radiation signals, which are focused onto the cell, to output voltage signals as a function of the radiation signals inputted thereto. The sensor exhibits a nonlinear gain response to different frequencies of input signals and compensation is provided by coupling the output of the sensor to a differentiating circuit which has a similar but relatively negative gain response. The output of the differentiating circuit is a substantial voltage replica of the infrared input signal and this voltage signal may be applied to a suitable utilization device such as one which records journal temperature and/or provides a suitable alarm when a sensed journal temperature exceeds a predetermined value.

Claims

1. An improved circuit for use in apparatus for detecting the temperature of railroad car wheel journals as a train passes a fixed wayside point whereby infrared signals are transmitted from the wheel journals to the apparatus at a frequency corresponding to the rate at which said wheels pass said wayside point, said circuit comprising:

a. sensor means including a pyroelectric cell for outputting a voltage signal having a magnitude which is a function of the infrared input signals applied thereto, said sensor means exhibiting a substantially flat gain response to input signals occurring at frequencies within a first range and a gain response which varies exponentially with an increase in the frequency of the input signals within a second range of frequencies higher than said first range; and

,

b. differentiating means responsive to the output of said sensor means to output a voltage signal having a magnitude porportional to the temperature of the wheel journal, said differentiating means having a substantially flat gain response to signals having a frequency within said first range and a gain response within said second range which varies exponentially at the same rate but in a direction opposite to that of said sensor means.

2. The invention in accordance with claim 1 wherein said sensor means includes means to effect a gain response in said second range which decreases.

3. The invention in accordance with claim 2 wherein said sensor means acts as an integrator within said second range of frequencies and is the electrical equivalent of a resistance-capacitance network having a resistor of a value R and a capacitor of a value C, said network having a transfer function F defined generally by the expression:

##EQU2## and wherein said differentiating means is a resistance-capacitance network having resistors of values R₁ and R₂ and a capacitor of a value C₁ and having a transfer function F₁ defined generally by the expression;

##EQU3##

4. The invention in accordance with claim 2

wherein said differentiating means comprises an operational amplifier having a feedback path between its output and an input thereof, said feedback path including resistive and capacitive components.

5. The invention in accordance with claim 1 wherein said first and second frequency ranges have a common boundary.

6. An improved circuit for use in apparatus for detecting overheated journals in railroad cars comprising:

a. sensor means including a pyroelectric cell for outputting a voltage signal in response to infrared radiation signals inputted thereto, said sensor means exhibiting a substantially flat gain response to input signals occurring within a first frequency range and a gain response which decreases exponentially with increasingly higher frequencies within a second frequency range of higher frequencies than those of said first range; and

,

b. differentiating means coupled to the output of said sensor means, said differentiating means having a substantially flat gain response to input signals having a frequency within said first range and a gain response to input signals within said second range which increases exponentially, with increasing frequencies, at substantially the same rate as the gain of said sensor means decreases whereby the output of said differentiating means is substantially a voltage representation of the infrared signals inputted to said sensor means.

7. The invention in accordance with claim 6 wherein said sensor means acts as an integrator within said second range of frequencies and is the electrical equivalent of a resistance-capacitance netowrk having a resistor of a value R and a capacitor of a value C, said network having a transfer function F defined generally by the expression:

##EQU4## and wherein said differentiating means is a resistance-capacitance network having resistors of values R₁ and R₂ and a capacitor of a value C₁ and having a transfer function F₁ defined generally by the expression;

##EQU5##

8. The invention in accordance with claim 6 wherein said differentiating means comprises an operational amplifier having a feedback path between its output and an input thereof, said feedback path including resistive and capacitive components.

9. The invention in accordance with claim 6 wherein said first and second frequency ranges are contiguous.

10. An apparatus for determining the temperature of railroad car wheel journals passing a location comprising:

a. optical means for focusing infrared signals originating at passing wheel journals at a point;

b. sensor means, including a pyroelectric cell disposed at the focal point of said optical means, for producing first voltage signals as a function of the infrared radiation impinging upon said cell, said sensor means exhibiting a gain response which is substantially constant for infrared signals occurring at rates within a first range and exhibiting a gain response which varies exponentially in a first direction for infrared signals occurring at rates within a second range higher than and contiguous to said first range;

c. differentiating means responsive to said first voltage signals from said sensor means to output second voltage signals representative of said infrared signals, said differentiating means having a substantially flat gain response for input signals occurring at rates within said first range and a gain response for signals occurring at rates within said second range which varies exponentially at the same rate but in a direction opposite to that of said sensor means; and

,

d. means responsive to said second voltage signals to at least provide an indication of when said infrared signals impingent on said pyroelectric cell indicate that the wheel journals are at a temperature exceeding a predetermined value.