Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – With auxiliary means to condition stimulus/response signals
Reexamination Certificate
1998-12-08
2001-10-09
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
With auxiliary means to condition stimulus/response signals
C324S076170
Reexamination Certificate
active
06300776
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for discrete-time reactance measurement in which the reactance is activated by a clocked generator device with an electric voltage an electric current or an electric charge, and a clocked analyzer device generates an output signal as a function of the reactance to be measured from discrete-time sampled values of the electric voltage, electric current or electric charge, the generator device and analyzer device being clocked in synchronism.
Capacitive and inductive sensors have found wide acceptance for measuring a plurality of physical variables. As a rule, such sensors cannot be analyzed statically, this being the reason why they need to be activated by a generator with an alternating voltage or alternating current. Various possibilities exist for determining the sensor reactance. Due to its good integratability, use is often made of the switched-capacitor technique in which each analysis cycle consists of one or more precharge phases (activation) and one or more measuring phases (analyzing), the switched-capacitor technique thus representing a discrete-time method.
Measuring capacitances by the switched-capacitor technique is known for example from the paper “A Switched-Capacitor Digital Capacitance Meter” by Hiroki Matsumoto and Kenzo Watanabe in the journal “IEEE Transactions on Instrumentation and Measurement”, vol. IM-35, No. 4, December 1986, pages 355-359, and from German Patent 35 44 187 A1. In this known method a constant clock is used for activation and analysis so that the time-spacings between the points in times of analysis are always the same. In keeping with the Nyquist sampling theorem it is known that the repetition frequency of the analysis must be at least twice as high as the highest frequency of the variable to be measured, the ratio of the analysis clock frequency to twice the value of the highest frequency of the variable to be measured being termed the oversampling rate. When this ratio is smaller than unity the Nyquist sampling theorem is violated and aliasing errors result.
In the majority of applications the changes in time of the reactance to be measured are relatively slow so that a high oversampling rate is possible as is also often made use of to improve the accuracy of measurement. However, due to external influencing factors, disturbing alternating signals are also coupled into the reactance to be measured. The frequencies of these disturbances may be in ranges which result in violation of the Nyquist sampling theorem. Aliasing then results in the interference signal being imaged on the wanted signal and thus in the reactance measurement being falsified. More particularly, it is in the more immediate vicinity of the whole number multiples of the analysis clock frequency (sampling frequency) that ranges highly sensitive to interference materialize.
On the other hand it is known to vary a system clock by frequency or phase modulation to reduce disturbing effects. Various known solutions in this respect read from EP 0 715 408 A1, and a further solution is stated in which an original clock is modulated by means of a phase modulator as a function of a random signal source. Described in DE 196 37 942 A1 is a method of modulating the detection clock of a digital oscilloscope in making use of a phase-locked loop.
SUMMARY OF THE INVENTION
As compared to this the invention is based on the object of reducing the influence of narrowband disturbances coupled into the system by aliasing in discrete-time clocked reactance measurements.
On the basis of the method as cited at the outset this object is achieved in accordance with the invention by the clock controlling the generator device and the analyzer device being varied in the same way by frequency or phase modulation.
The method in accordance with the invention results in the effect that as compared to conventional measurement methods employing a constant activation and analysis clock the sensitivity in the vicinity of multiples of the sampling frequency is less and spread over a broader frequency range. Thus, any disturbance not covering the full bandwidth of a sensitive range has less influence on the measurement than when measuring with a constant clock.
A device for implementing the method in accordance with the invention including a clocked generator device for activating the reactance to be measured with an electric voltage, an electric current or an electric charge, a clocked analyzer device for generating an output signal as a function of the reactance to be measured from discrete-time sampling values of the electric voltage, the electric current or the electric charge, and a clock generator producing a clock controlling the generator device and the analyzer device in common comprises in accordance with the invention a control device for modulating the frequency or phase of the clock generated by the clock generator.
Further aspects and further embodiments of the method and device in accordance with the invention are characterized in the sub-claims.
REFERENCES:
patent: 4387338 (1983-06-01), Hecht et al.
patent: 4404517 (1983-09-01), Machida
patent: 4570116 (1986-02-01), Tedd et al.
patent: 5115189 (1992-05-01), Holcomb
patent: 5699005 (1997-12-01), Menkhoff et al.
patent: 36 11 683 (1987-10-01), None
patent: 0 421 953 A1 (1987-10-01), None
Hiroki Matsumoto, A Switched-Capacitor Digital Capacitance Meter, IEEE Transactions on Instrumentation and Measurement, vol. IM-35, No. 4, Dec. 1986.
Lalla Robert
Schreiber Ronald
Bose McKinney & Evans LLP
Endress + Hauser GmbH + Co.
Kerveros J.
Metjahic Safet
LandOfFree
Method and device for discrete-time reactance measurement does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for discrete-time reactance measurement, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for discrete-time reactance measurement will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2612125