US 4,360,880 A · Recirculating RMS AC conversion method and apparatus with fast mode

Abstract

A signal whose RMS value is to be accurately determined is first converted into DC form by a relatively inaccurate RMS converter, such as a thermal RMS converter (15). The result is a first converter signal (Y.sub.1), which is stored for recirculation in a suitable storage device, such as a sample and hold circuit (17). Thereafter, the signal stored in the storage device is recirculated to the converter to create a second converter signal (Y.sub.2). Then, the second converter signal is subtracted from the doubled value of the first converter signal (2Y.sub.1 -Y.sub.2) to produce a corrected RMS signal (X). The difference between the first converter signal (Y.sub.1) and the corrected RMS signal (X) is then determined. This error signal (E) is stored. Next, a decision is made as to whether or not a fast mode of operation is to be followed. If it is not to be followed the corrected RMS signal is displayed. If the fast mode is to be followed, the signal whose RMS value is to be accurately determined is reapplied to the RMS converter. The result is a third converter signal from which the error signal is subtracted to produce a corrected signal that accurately represents the RMS value of the reapplied signal. This corrected signal is then displayed or applied to other downstream subsystems, such as signal analyzers or recorders. The fast mode steps are then repeated.

Claims15

Dependent claims

A method of accurately determining the RMS value of an unknown signal comprising the steps of:

(a) applying the unknown signal to an RMS converter having a relatively smooth transfer curve to produce a first converter signal;
(b) recirculting said first converter signal back to said RMS converter to produce a second converter signal;
(c) combining said first and second converter signals in accordance with the relationship to 2Y.sub.1 -Y.sub.2 to obtain a corrected signal, X, that accurately represents the RMS value of the unknown signal, where Y.sub.1 is directly related to said first converter signal and Y.sub.2 is directly related to said second converter signal;
(d) combining said first converter signal with said corrected signal in accordance with the relationship Y.sub.1 -X to obtain an error signal;
(e) again applying the unknown signal to said RMS converter to produce a third converter signal;
and,
(f) subtracting said error signal from said third converter signal to obtain a corrected signal that accurately represents the RMS value of the reapplied unknown signal.

4 more elements

Apparatus for accurately determining the RMS value of an unknown signal comprising:

(a) RMS conversion means having a relatively smooth transfer curve for converting an input signal into a DC signal proportional to the RMS value of the input signal;
(b) recirculating means connected to the output of said conversion means for recirculating the output of said conversion means back to the input of said conversion means;
(c) controllable switch means connected to said RMS conversion means and said recirculating means for selectively applying either an unknown signal or the output of said recirculating means to the input of said RMS conversion means;
and,
(d) control and combining means connected to said RMS conversion means and said controllable switch means for:
(i) causing said controllable switch means to apply an unknown signal to said RMS conversion means and receiving the output of said RMS conversion means, said output forming a first converter signal;
(ii) causing said controllable switch means to apply the output of said recirculating means to the input of said RMS conversion means and receiving the output of said RMS conversion means, said output forming a second converter signal;
(iii) combining said first and second converter signals in accordance with the relationship to 2Y.sub.1 -Y.sub.2 to obtain a corrected signal, X, that accurately represents the RMS value of the unknown signal, where Y.sub.1 is directly related to said first converter signal and Y.sub.2 is directly related to said second converter signal;
(iv) combining said first converter signal with said corrected signal in accordance with the relationship Y.sub.1 -X to obtain an error signal;
(v) causing said controllable switch means to again apply said unknown signal to the input of said RMS conversion means and receiving the output of said RMS conversion means, said output forming a third converter signal;
and,
(vi) subtracting said error signal from said third converter signal to obtain a corrected signal that accurately represents the RMS value of the reapplied unknown signal.

9 more elements

Dependencies are inferred from the claim text.

Recirculating RMS AC conversion method and apparatus with fast mode

Life of this patent

Recirculating RMS AC conversion method and apparatus with fast mode

Life of this patent

Abstract

Claims15