Method and apparatus for adjustment of acquisition parameters in a data acquisition system such as a digital oscilloscope

A method of setting the acquisition parameters for a data acquisition system which receives an input signal containing a repetitive waveform and which has a memory in which digital data sampled from the input waveform is stored, the data acquisition system having a maximum sampling rate, memory capacity, and voltage range, comprising the steps of:

• (a) setting initial values for the acquisition parameters, including setting the sampling rate to maximum, setting the record length stored in the memory to the maximum capacity of the memory, setting a pretrigger to one-half of the points in the memory, setting a voltage range on the input signal to maximum, and setting a trigger level to a selected level;
• (b) acquiring waveforms from the input signal repetitively, adjusting the voltage range to accept the full range of the input signal with no saturated values, finding a trigger level of the input signal, and then acquiring a waveform and calculating the central time and rms duration of the waveform;
• (c) setting the record length for the data to be stored in the waveform memory and the pretrigger amount in accordance with the rms duration and the central time calculated for the waveform;
• then
• (d) acquiring another waveform from the input signal, searching for a trigger level and adjusting the voltage range so that the input waveform will be within the range of the system and without any saturated values, then performing spectral analysis on the waveform data acquired to provide a spectrum and determining from the spectrum the maximum significant frequency content of the waveform, then setting the sampling rate such that the waveform is sampled without aliasing, based upon the maximum significant frequency content and then setting the record length in the memory and the pretrigger amounts so as substantially to span plus or minus 3 rms durations of the waveform.

A method of determining the length of a waveform in an input signal that is received repetitively by a data acquisition system, comprising the steps of:

• (a) setting initial acquisition parameters for the data acquisition system including sampling rate, record length of the data to be stored in a memory of the data acquisition system, a pretrigger amount of data points to be stored in the memory prior to the occurrence of a trigger event, a selected initial trigger level, and a voltage range;
• (b) acquiring a waveform repetitively from the input signal and finding a trigger level which occurs within the record length of the waveform, determining a sampling rate such that two triggers occur within the total range of data acquired, adjusting the voltage range to accept the input signal with no saturation of the sampled values of the input waveform, and then calculating the central time and rms duration of the waveform in the input signal;
• and
• (c) setting the record length equal to a selected multiple of the calculated rms duration.

Digital oscilloscope apparatus comprising:

• (a) a waveform memory having a maximum memory capacity;
• (b) sampling means for sampling a time varying input signal to produce digital data corresponding to the waveform of the signal and storing the data in the waveform memory, the sampling means having a maximum sampling rate and input voltage range;
• (c) display means for receiving digital data to provide a visual display of the waveform corresponding to the received data on a display screen;
• (d) trigger generator means for receiving the input signal and providing a trigger signal at a selected trigger level;
• (e) CPU control means for controlling the waveform memory, sampling means, the display means, and the trigger generator means, for setting initial values for acquisition parameters for the input signal waveform including sampling rate, trigger level, voltage range, pretrigger amount and the length of the record in the waveform memory of the data acquisition system, for using the initial acquisition parameters to acquire data corresponding to an input waveform, and for analyzing the acquired waveform data and reacquiring the input waveform repetitively to determine the length of the input waveform, the voltage range of the waveform, and the frequency content of the waveform, and for adjusting the acquisition parameters so that for the input waveform, the voltage range allows all waveform data to be acquired without saturation, the sampling rate is sufficient to avoid aliasing of the highest significant frequency components of the input waveform while accommodating all or substantially all of the waveform within the memory capacity of the waveform memory at a selected trigger level and pretrigger amount.

Digital oscilloscope apparatus comprising:

• (a) a waveform memory having a maximum memory capacity;
• (b) sampling means for sampling a time varying input signal to produce digital data corresponding to the waveform of the signal and storing the data in the waveform memory, the sampling means having a maximum sampling rate and input voltage range;
• (c) display means for receiving digital data to provide a visual display of the waveform corresponding to the received data on a display screen;
• (d) trigger generator means for receiving the input signal and providing a trigger signal at a selected trigger level;
• (e) CPU control means for controlling the waveform memory, the means for sampling, the display means and the trigger generator means, for setting initial values for the acquisition parameters for acquiring a waveform, including setting the sampling rate of the sampling means to its maximum, setting the record length stored in the waveform memory to the maximum capacity of the memory, setting a pretrigger to one-half of the points in the memory, setting a voltage range on the input signal to the sampling means to a maximum, and setting a trigger level in the trigger generator to a selected level for acquiring waveforms from the input signal repetitively, adjusting the voltage range of the sampling means to accept the full range of the input signal with no saturated values, for finding a trigger level of the input signal, and then acquiring a waveform and calculating the central time and rms duration of the waveform, for setting the record length for the data to be stored in the waveform memory and the pretrigger amount in accordance with the rms duration and the central time calculated for the waveform, and for acquiring another waveform from the input signal, searching for a trigger level and adjusting the voltage range so that the input waveform will be within the range of the sampling means without any saturated values, for then performing spectral analysis on the waveform data acquired to provide a spectrum and determining from the spectrum the maximum significant frequency content of the waveform, for then setting the sampling rate of the sampling means such that the maximum significant frequency content of the waveform is sampled without aliasing and then setting the record length in the memory and the pretrigger amounts so as substantially to span plus or minus 3 rms durations of the waveform.

Digital oscilloscope apparatus comprising:

• (a) a waveform memory having a maximum memory capacity;
• (b) sampling means for sampling a time varying input signal to produce digital data corresponding to the waveform of the signal and storing the data in the waveform memory, the sampling means having a maximum sampling rate and input voltage range;
• (c) display means for receiving digital data to provide a visual display of the waveform corresponding to the received data on a display screen;
• (d) trigger generator means for receiving the input signal and providing a trigger signal at a selected trigger level;
• (e) CPU control means for controlling the waveform memory, the sampling means, the display means, and the trigger generator means, for setting initial acquisition parameters including the sampling rate of the sampling means, the record length of the data to be stored in the waveform memory, a pretrigger amount of data points to be stored in the memory prior to the occurrence of a trigger event, a selected initial trigger level in the trigger generator means, and the voltage range of the sampling means, for then acquiring a waveform repetitively from the input signal and finding a trigger level which occurs within the record length of the waveform, for determining a sampling rate such that two triggers occur within the total range of data acquired, for adjusting the voltage range to accept the input signal with no saturation of the sampled values of the input waveform in the sampling means for calculating the central time and rms duration of the waveform in the input signal, and for setting the record length equal to a selected multiple of the calculated rms duration.