Measuring circuit for a capacitive sensor for distance measurement and/or space monitoring

• US 6,486,681 B1
• Filed: 03/22/2001
• Issued: 11/26/2002
• Est. Priority Date: 08/10/1998
• Status: Expired due to Fees

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Weber, Jens, Hoetzel, Juergen, Rech, Wolf-Henning, Tschiskale, Ega
• Primary Examiner(s): Le, N.
• Assistant Examiner(s): KERVEROS, DEMETRIOS C
• Application Number:
  US09/762,461
• Time in Patent Office: 614 Days
• Field of Search: 324/662, 324/663, 324/687, 324/688, 324/686, 324/671
• US Class Current: 324/662
• CPC Class Codes: G01S 13/04 Systems determining presence of a target based on relative movement of target G01S13/56
• CPC Class Codes: G01S 7/03 Details of HF subsystems specially adapted therefor, e.g. common to transmitter and receiver
• CPC Class Codes: G08B 13/26 by proximity of an intruder causing variation in capacitance or inductance of a circuit
• CPC Class Codes: H03K 2217/960765 Details of shielding arrangements

Abstract

In a measuring circuit for a capacitive sensor for distance measurement and/or space monitoring comprising sensor wire and shielding electrode, a sine signal is applied to the shielding electrode. The sensor wire is connected, via a shielded cable, with one input of an input amplifier which serves as current-voltage converter and whose supply voltage is likewise influenced by the sine signal. The output of the input amplifier is connected with one input of a phase-dependent rectifier arrangement, the sine signal is applied to the other input of the phase-dependent rectifier arrangement, and its output is connected to an analog-to-digital converter.

Claims

1. Measuring circuit for a capacitive sensor (1) for distance measurement and/or space monitoring comprising sensor wire (2) and shielding electrode (3), characterized in that a sine signal is applied to the shielding electrode (3), in that the sensor wire (2) is connected, via a shielded cable (4), with one input of an input amplifier (5) which serves as current-voltage converter and whose supply voltage is likewise influenced by the sine signal, in that the output of the input amplifier (5) is connected with one input of a phase-dependent rectifier arrangement (11), the sine signal is applied to the other input of the phase-dependent rectifier arrangement (11) and its output is connected to an analog-to-digital converter (12).

2. Measuring circuit according to claim 1, characterized in that the input amplifier (5) is a negative feedback differential amplifier for a capacitively induced differential current whose inverting input (17) is connected with the sensor wire (2) and whose noninverting input (18) is connected to a voltage divider (19, 21) which is connected between a constant voltage source (7) and the sine signal source (6), wherein the resistor (21) of the voltage divider connected with the sine signal source (6) is connected in parallel with a capacitor (22).

3. Measuring circuit according to claim 2, characterized in that the differential amplifier is an operational amplifier (16) whose supply voltage is stabilized by a voltage regulator relative to the voltage of the shielding electrode.

4. Measuring circuit according to claim 2, characterized in that the shielding electrode (3) of the sensor (1) is connected with the sine signal source (6) via the shielding of the shielded cable (4).

5. Measuring circuit according to claim 1, characterized in that a subtraction stage (8) is provided between the input amplifier (5) and the phase-dependent rectifier arrangement (11), wherein the positive input of the subtraction stage (8) is connected with the output of the input amplifier (5) and the sine signal is applied to the negative input of the subtraction stage (8).

6. Measuring circuit according to claim 5, characterized in that a filter (9) is provided at the output of the subtraction stage (8).