H - Electricity – 05 – B
Patent
H - Electricity
05
B
327/2.51
H05B 6/68 (2006.01) G01K 7/00 (2006.01)
Patent
CA 2001652
ABSTRACT An improved pyroelectric sensing apparatus for use in applications such as microwave ovens, where it is necessary to sense the presence of steam generated by a food item being heated and to generate a load-stop signal which shuts down the heating mechanism at the appropriate time. The apparatus comprises a pyroelectric element which issues a succession of pulses upon contact by steam on its sensing surface, detection means for detecting pulses of above a predetermined level by sampling with predetermined sampling timings, succession period detection means for detecting the time period of the succession of pulses, and comparison means for comparing the time period detected by the succession period detection means with a predetermined reference time period and issuing a control output signal when the detected time period is longer than the reference time period. The pyroelectric sensing apparatus in accordance with the present invention can make accurate and reliable signal detection because of its high S/N ratio, since noise output spikes caused by mechanical shock or electric shock are prevented from producing the load-stop signal, by taking advantage of the characteristic of the pyroelectric detection signal caused by boiling steam having low frequency components.
Kasai Isao
Kashimoto Takashi
Yamaguchi Kimiaki
Yoshino Koji
Borden Ladner Gervais Llp
Matsushita Electric Industrial Co. Ltd.
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