Temperature detector

• US 5,257,864 A
• Filed: 02/10/1992
• Issued: 11/02/1993
• Est. Priority Date: 08/19/1989
• Status: Expired due to Fees

• Current Assignee: Hamanishi Sangyo Company
• Original Assignee: Hamanishi Sangyo Company
• Inventors: Nomura, Yasuhisa
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): GUTIERREZ, DIEGO F
• Application Number:
  US07/829,063
• Time in Patent Office: 631 Days
• Field of Search: 374/163, 374/183, 374/184
• US Class Current: 374/163
• CPC Class Codes: G01K 7/34 using capacitative elements capacitors per se H01G
• CPC Class Codes: G01K 7/343 the dielectric constant of which is temperature dependant

Abstract

Zero-cross points of an ac voltage waveform (v) applied to a heat-sensitive wire (1) and an ac current waveform (i) flowing into the heat-sensitive wire (1) are detected by a zero voltage detection unit (3) and a zero current detection unit (4), and the interval between the zero-cross points of voltage and current is measured by a measuring unit (7). The measured interval corresponds to the phase angle (φ) between the voltage and current waveforms, and the phase angle (φ) depends on the specific resistance (ρ) and permitivity (ε) of the heat-sensitive wire (1). This relation is utilized for temperature measurement. The relation between the phase angle (φ) and the specific resistance (ρ) and permitivity (ε) is independent of the size of the heat-sensitive wire. Therefore, the temperature can be correctly measured even when the wire is made of a material which is not rigid enough to keep its size constant.

Claims

1. A temperature detector for detecting a temperature by applying an ac power source across coaxial internal and external conductors of a heat-sensitive wire, comprising:

zero voltage detecting means, parallelly connected to said heat-sensitive wire, for detecting zero-cross points of an ac voltage waveform applied across both of said coaxial internal and external conductors;

zero current detecting means, connected in series with said heat-sensitive wire, for detecting zero-cross points of an ac current waveform flowing across both of said coaxial internal and external conductors; and

interval measuring means for receiving outputs from said zero voltage detecting means and said zero current detecting means to measure an interval between the zero-cross points of the ac voltage waveform and the ac current waveform,

said zero current detecting means having at least the same impedances of positive and negative components of the ac current waveform to prevent generation of an unbalanced component in the ac current waveform flowing across both of said coaxial internal and external conductors,

a temperature measurement value being obtained from an output of said interval measuring means.

2. The temperature detector according to claim 1, wherein a thermistor is buried between said coaxial internal and external conductors.

3. The temperature detector according to claim 2, wherein said thermistor is made of a polymer compound and said coaxial internal and external conductors are flexible.

4. The temperature detector according to claim 1, wherein said zero voltage detecting means and said zero current detecting means respectively apply an ac voltage waveform to said heat-sensitive wire and supply an ac current waveform which flows into said heat-sensitive wire as base inputs of transistors, first and second diodes each having a polarity opposite to that of a corresponding transistor respectively being connected between a base and an emitter of each of said transistors, and ON/OFF threshold levels of said transistors are set to an approximately zero voltage level and an approximately zero current level, respectively.

5. The temperature detector according to claim 1, wherein said interval measuring means comprises counter means for counting clock pulses in an interval between the zero-cross points.

6. The temperature detector according to claim 1, wherein said interval measuring means comprises an integrator for integrating a pulse having a width corresponding to the interval between the zero-cross points to form a voltage signal corresponding to a temperature.

7. The temperature detector according to claim 1, wherein said zero voltage detecting means and said zero current detecting means comprise:

a rectifier for rectifying the ac voltage waveform applied to said heat-sensitive wire and the ac current waveform flowing into said heat-sensitive wire; and

a detecting transistor having ON/OFF threshold levels which are set to a zero voltage level and a zero current level.

8. The temperature detector according to claim 1, wherein said interval measuring means comprises:

measurement means for generating a measurement value corresponding to of the ac voltage waveform applied to said heat-sensitive wire and the ac current waveform flowing into said heat-sensitive wire; and

calculating means for calculating a temperature measurement value on the basis of measurement values of the frequencies and a measurement value of the interval of the zero-cross points.

9. The temperature detector according to claim 1, wherein said zero voltage detecting means comprises:

a first transistor having a base coupled to the ac voltage waveform applied to said heat-sensitive wire, an ON/OFF threshold of said first transistor being set to an approximately zero voltage level; and

a first diode, of polarity opposite said first transistor, coupled between the base and an emitter of said first transistor,

said zero current detecting means comprises

a second transistor having a base coupled to the ac current waveform flowing into said heat-sensitive wire, an ON/OFF threshold of said second transistor being set to an approximately zero current level; and

a second diode, of polarity opposite said second transistor, coupled between the base and an emitter of said second transistor.