Dual-frequency microwave sensor

• US 20040257228A1
• Filed: 04/30/2004
• Published: 12/23/2004
• Est. Priority Date: 10/30/2001
• Status: Active Grant

• Current Assignee: Optex Company Limited (OPTEX GROUP Co., Ltd.)
• Original Assignee: Optex Company Limited (OPTEX GROUP Co., Ltd.)
• Inventors: Tsuji, Masatoshi
• Granted Patent: US 7,079,029 B2
• Time in Patent Office: Days
• US Class Current: 340/552
• CPC Class Codes: G01S 13/38 wherein more than one modulation frequency is used
• CPC Class Codes: G01S 7/4021 of receivers

Abstract

A threshold level is set in advance that has varied signal level values of reflected waves for which an object detection signal is to be dispatched, the values varying in response to a distance to the object. In regard to discriminating a phase difference of respective waves reflected from an object and the signal level of the waves reflected from that object, and obtaining two distances to an object due to fold-over error when using only the phase difference, the present invention uses the signal level of the reflected waves to judge which distance is the correct distance.

Claims

1. A dual-frequency microwave sensor, which transmits two microwaves of different frequencies and, when an object is present in a transmission direction of the microwaves, receives reflected waves of the microwaves from the object and measures a distance to the object based on the reflected waves, comprising:

an object detection means for measuring the distance to the object based on a phase difference of the respective reflected waves and a signal level of the reflected waves from the object.

2. A dual-frequency microwave sensor, which transmits two microwaves of different frequencies and, when an object is present in a transmission direction of the microwaves, receives reflected waves of the microwaves from the object and measures a distance to the object based on the reflected waves, comprising:

an object detection means that measures the distance to the object based on a phase difference of the respective reflected waves and a signal level of the reflected waves from the object, and dispatches an object detection signal only when the measured distance is shorter than a predetermined distance.

3. The dual-frequency microwave sensor according to claim 2,

wherein a threshold level is set in advance that has varied signal level values of reflected waves for which an object detection signal is to be dispatched, the values varying in response to a distance to the object,

wherein the object detection means is configured to dispatch the object detection signal only when the received reflected waves are of a signal level that exceeds the threshold level.