Remote temperature change warning system

Claim 1

A remote temperature change warning system for a refrigeration vehicle having existing vehicular wiring comprising a temperature sensing circuit located in the refrigeration compartment of said refrigeration vehicle, said temperature sensing circuit comprising a linear electrical transducer means for producing at the output thereof a d.c. electrical signal proportional to the temperature in said refrigeration compartment, a frequency modulation circuit means in electrical connection with the output of said electrical transducer means, said frequency modulation circuit means generating at its output an a.c. electrical signal having a frequency proportional to the d.c. electrical signal produced by said electrical transducer means whereby an a.c. electrical signal is generated by said temperature sensing circuit having an audio frequency proportional to the temperature in said refrigeration compartment, and means for approximately matching the output impedance of said temperature sensing circuit to the impedance of said existing vehicular wiring, and a detection circuit located on said vehicle remote from said temperature sensing circuit, said detection circuit comprising a frequency discriminator means for producing a d.c. electrical signal which is proportional to the frequency of an inputted a.c. electrical signal, and a temperature condition indication means electrically driven according to the level of the d.c. electrical signal produced by said frequency discriminator means, the output of said temperature sensing circuit and the input of said detector circuit being coupled to and electrically connected through the existing electrical wiring of said refrigeration vehicle whereby the indication on said temperature condition indication means is electrically determined by the temperature in the remote refrigeration compartment of said refrigeration vehicle.