Apparatus for producing a digital electrical representation of a peak value of an analog signal

Abstract

Abstract A digital display of the peak value of an input analog signal is obtained by using a capacitor-storage feedback circuit to derive and store a signal substantially equal to the peak value of the input analog signal, and then comparing this stored peak value with the instantaneous value of the analog signal to produce a HOLD signal whenever the occurrence of a peak is indicated by the analog signal falling below the stored signal by a predetermined amount. A digital voltmeter is supplied directly with the analog signal so as to produce a continuously changing digital output indication of the value of the analog signal except when the HOLD signal indicating the occurrence of a peak is applied to the digital voltmeter to prevent the digital indication from changing further, thereby holding the peak digital indication for a very long period of time. If the analog signal later rises to a higher peak, the digital voltmeter will follow this and hold at a digital number representing the subsequent peak value. By disabling the HOLD control circuitry, the digital voltmeter can be permitted to follow the analog signal at all times when it is not desired to display merely the peak value of the signal. The storage circuit is preferably of the type in which a capacitor is intermittently charged by pulses of current from a constantcurrent source by means of an electronic switch which is turned on each time a comparator indicates that the analog signal exceeds the feedback signal from the charged capacitor. The peak reading on the digital voltmeter remains exactly constant even though the voltage across the capacitor may decay substantially, so long as it does not decay so much as to fall below the analog signal level by a predetermined amount. Thus, particularly for applications in which the analog signal peak is followed by a relatively large and rapid decrease in analog signal, an extremely long hold time for the digital output reading can be obtained without requiring an expensive low-leakage capacitor or associated circuits. In the preferred embodiments, the apparatus can be utilized to enable digital indication of the peak of force exerted on a test object by a test stand, and of the corresponding value of displacement (e.g. compression or elongation) of a test specimen in the test stand.

Inventors

• 👤 Bernd R Guggolz

Bibliographic Details