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| OF A PREFERRED EMBODIMENT FIG. 1 illustrates in a partial pictorial, partial schematic diagram, a ... |
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| OF A PREFERRED EMBODIMENT Referring now to FIG. 1A, this figure depicts a prior art pulse width ... |
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| Dual A/C and D/C input powered portable battery charger |
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| Method and apparatus for removing deposits from highly heated surfaces |
| OF PREFERRED FORM OF THE INVENTION FIGS. 1 and 2 illustrate somewhat diagrammatically a long ... |
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| Method and device for monitoring deterioration of battery |
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| Battery capacity calculator and method of calculating battery capacity |
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Circuit for determining the internal resistance of a linear lambda probe
| Details |
Inventors: Bolz, Stephan;
Assignee: Siemens Aktiengesellschaft (Munich, DE)
Primary Examiner: Deb; Anjan K.
Assistant Examiner:
Attorney, Agent or Firm: Baker Botts L.L.P.
A device for measuring the probe impedance of a linear lambda probe of an internal combustion engine which is caused by an AC current measurement signal which is fed into the lambda probe, comprises a voltage amplifier for amplifying an AC voltage which drops across the probe impedance, and a rectifier for rectifying the amplified AC voltage, wherein the rectifier is a synchronous demodulator, by which in each case the upper and lower amplitude of the AC voltage signal is sampled with its frequency, filtered and stored, and by which the difference of the stored signals is amplified with a gain factor and made available as output signal at its output for controlling the temperature of the lambda probe. |
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DETAILED DESCRIPTION The object of the invention is to improve the measurement of the impedance (of the internal resistance) Ri of a linear lambda probe and to reduce the error in the rectification of the AC voltage signal, and to reduce the sensitivity to electromagnetic interference pulses (EMC).
In general terms, the object of the invention is to acquire precisely the peak-to-peak amplitude value (Vss) of an AC voltage signal whose phase is known and on which a DC voltage is superimposed.
This object can be achieved by a device for measuring the probe impedance of a linear lambda probe of an internal combustion engine which is caused by an AC current measurement signal which is fed into the lambda probe, having a voltage amplifier for amplifying an AC voltage which drops across the probe impedance, and having a rectifier for rectifying the amplified AC voltage, wherein the rectifier is a synchronous demodulator, by which in each case the upper and lower amplitude of the AC voltage signal is sampled with its frequency, filtered and stored, and by which the difference of the stored signals is amplified with a gain factor and made available as output signal at its output for controlling the temperature of the lambda probe.
An oscillator can be provided from whose output signal both the AC current measurement signal and the control signals for the synchronous demodulator are acquired.
The synchronous demodulator may comprise a first sample and hold circuit in which the upper amplitude of the input signal is sampled and held, a second sample and hold circuit in which the lower amplitude of the input signal is sampled and held, a decoupling amplifier connected downstream of each sample and hold circuit, and a differential amplifier which forms a differential signal from the output signals of the two decoupling amplifiers and makes available as output signal at the output of the synchronous demodulator as control signal for controlling the temperature of the lambda probe.
The resistor and the capacitor of each sample and hold circuit may form, in the sampling phase, a low-pass filter for the integrated averaging of the input signal, and the capacitors may act as holding capacitors in the hold phase
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Electrical and Wave 
