1. Field of the Invention
The present invention relates generally to electronic signal measurement apparatus, and more particularly to a short-duration anomalous signal event acquisition and display system wherein the maximum and minimum frequency of a pulse train signal over a predefined time period is detected, stored, processed and then read out at a slower rate for display in electronic strip chart format to highlight signal anomalies.
2. Description of the Prior Art
In the automotive repair field, as well as in other fields, it has long been important to have instruments available for measuring electrical signals occurring at various points within the numerous electrical circuits and signal paths resident in an automobile. Measurements of parameters such as current, voltage, resistance, signal frequency, etc. enable a repair technician to locate and diagnose the numerous problems that occur in a vehicle. Such parameters are typically measured using available apparatus ranging from simple voltage, current and resistance-measuring meters to sophisticated, computerized electronic diagnostic equipment.
Among the most difficult conditions to measure are the intermittent faults commonly referred to as xe2x80x9cglitchesxe2x80x9d, i.e. short duration signal events, one type of which being intermittent missing pulses from a periodic signal. Normal repetitive periodic signals are illustrated by FIGS. 1a, 1b, and 1c, where FIG. 1a is periodic square wave, FIG. 1b is a periodic triangular wave, and FIG. 1c is a periodic clipped sine wave. All three of these normal periodic signals have a pulse in every cycle. The type of glitches discussed herein relate to missing pulses from a periodic signal. For example, a normal operating subsystem would generate a repetitive pulse train having no missing pulses like the signal illustrated in FIG. 1a, while a faulty subsystem might generate a repetitive pulse train with intermittent missing pulses like that of FIG. 2. Some of the automotive components or subsystems generating periodic signals include crank shaft sensors, cam shaft sensors, mass air flow sensors, vehicle speed sensors, and in some vehicles, pressure sensors. The frequency of these signals typically ranges from xc2xd Hz to 20 kHz. While the disclosure herein discusses square wave forms, the principles and concepts equally apply to other types of periodic signals.
Previous measurement systems such as the oscilloscope and frequency counters prove to be problematic in identifying and displaying these types of glitches. For example, an oscilloscope requiring complex and expensive electronics would have a difficult time triggering on a periodic signal with missing pulses simply because it is difficult to trigger on non-existent or intermittently existing signals. Even if the oscilloscope does manage to trigger on the signal and display the signal, due to the intermittent nature of such glitches, the missing pulse(s) may be displayed for a fraction of a second on the scope and an operator of the scope may fail to observe or identify such anomaly.
In the case of frequency counters, the frequency of a periodic wave form is taken over a relatively long period of time (up to 1 second.) and a frequency value in accordance with the classical definition of frequency in cycles per second is calculated and displayed. This frequency value provides no indication of missing pulses and tends to hide any anomalies or missing pulses within the signal. A more indicative value would be the maximum and minimum instantaneous frequency of a periodic signal calculated over one or more periods of the periodic signal where such value can be displayed in a histogramic format allowing the operator to observe changes in frequency of a periodic signal to identify missing pulses.
There is thus a need for a relatively simple means for detecting and indicating the occurrence or non-occurrence of glitches in electrical circuits. Furthermore, there would be an advantage to a device that xe2x80x9ccapturesxe2x80x9d a glitch and displays its occurrence in a continuously moving histogramic format so that the user would not have to carefully watch the indicator to notice the transient occurrence of a glitch.
It is therefore an object of the present invention to provide an improved apparatus for monitoring electrical signals to detect and indicate the occurrence or non-occurrence of rapidly varying events, commonly referred to as glitches.
Another objective of the present invention is to provide glitch-detection and display apparatus that is simple to use and relatively low in cost.
Another object of the present invention is to provide apparatus of the type described which allows workers not experienced in the use of complex test instruments to observe short duration faults.
Still another object of the present invention is to provide apparatus of the type described that does not rely on user observation of the fault at the instant of its occurrence.
Yet another object of the present invention is to provide a system of the type described for detecting rapidly varying events using limited computational capacity for the event to be detected.
Briefly, the present invention is embodied in the form of a hand-held instrument which includes circuits for detection of missing pulses from a repetitive pulse train and including signal detection circuits for capturing the rising and/or falling edges of an input signal, time-stamping the captured edges, calculating the maximum and minimum instantaneous frequency over a specified time period, and displaying such frequency values. Instantaneous frequency values between any two adjacent edges are calculated based upon the time-stamps of the edges. The instantaneous frequency values in a specified time period are then sorted to find the minimum and maximum frequency values for that time period. These instantaneous frequency values are displayed in the form of a histogram evidencing the occurrence or lack of occurrence of missing pulses from the input signal.
An important advantage of the present invention is that it indicates the occurrence of otherwise difficult-to-detect events in a readily perceptible fashion.
Another advantage of the present invention is that it provides a histographic display of the occurrence of the events over a period of time.
Still another advantage of the present invention is that it can be used by workers inexperienced in the use of sophisticated test equipment.
These and other objects and advantages of the present invention will no doubt become apparent to those skilled in the art after having read the following detailed description of the preferred embodiment which is illustrated in the several figures of the drawing.