Eg&g Instruments, Inc.

Perkinelmer Instruments LLC

The Perkin-Elmer Corporation

Advanced Measurement Technology, Inc.

Russell D Bingham

Dale A Gedcke

Rex C Trammell

Jeffrey V Peck

Jesse Ursery

Timothy R Twomey

Ronald M Keyser

Susan Haywood

A method and apparatus for precision time interval measurement in a time-of-flight mass spectrometer (TOF-MS). The method and apparatus produces an instrument capable of measuring bursts of data occurring at rates much higher than the average data rate. An asynchronous serial stream of data, consisting of a start pulse followed by an arbitrary number of stop pulses, repeated an arbitrary number of times, is converted into a digital stream of data synchronized to a precision master clock. Conversion of the asynchronous, analog data to synchronous digital data simplifies the measurement task by allowing the use of powerful, low-cost digital logic in the measurement.

Method and apparatus for precision time interval measurement

An automatic pole-zero (APZ) adjustment circuit for an ionizing radiation spectroscopy system. An output of a preamplifier is sampled to identify the decay time constant of the preamplifier output. A correction based upon the identified decay time constant is generated by a correction signal generator and applied through either an analog pole-zero adjustment network or a programmable digital shaping filter to accomplish pole-zero correction.

Automatic pole-zero adjustment circuit for an ionizing radiation spectroscopy system and method

A differential correction apparatus for use with a spectroscopy device. The spectroscopy device simultaneously produces two histograms corresponding to the spectrum acquired. The first histogram contains the counts recorded by a differential correction method (DCM), giving the best estimate of the counts per channel in the absence of dead time. The second histogram is the error spectrum, giving the variance of the counts in each channel of the first spectrum. The two spectra have the same size, true acquisition time, and energy calibration with the only difference being the number of counts in each channel. By obtaining both histograms, it is possible to both obtain an accurate spectrum when the energy peaks have varying decay times and retain the necessary information about the spectrum to allow the statistical error to be calculated.

Differential correction method and apparatus

An automatic pole-zero (APZ) adjustment circuit for an ionizing radiation spectroscopy system. An amplitude histogram of an acquired spectrum is obtained. The shape of a selected peak from the amplitude histogram is analyzed for peak shape distortion indicating the existence of undershoot or overshoot. An analog correction signal generated by a pole-zero adjustment network is added to cancel existing undershoot or overshoot, thereby minimizing distortion of the peak shape. In an alternate embodiment, the correction signal is a digital transformation algorithm applied to a programmable digital shaping filter, thereby digitally minimizing distortion of the peak shape.

A digital signal averager for averaging data collected by an analog detector is provided. The digital signal averager includes an analog-to-digital converter for converting the analog detector output to a digital signal for processing, a timing device for generating delayed timing pulses for sequencing operation of the digital signal averager, an averaging device for summing and storing data. The delayed timing pulses allow data to be acquired by the ADC at a series of variably offset timing sequences relative to a trigger pulse. Offsetting the data acquisition timing sequences by time slices smaller than the actual sample rate of the ADC allows data to be acquired at a higher effective sampling rate. One complete series of offset timing sequences provides a data set containing all the information which would be acquired by a ADC having a faster sampling rate. Accuracy of the data is further enhanced by a series of parallel averaging devices, including one processing device and multiple memory devices, which perform real-time averaging of data. A digital signal processor applies a method for data compression to the averaged data to reduce data transfer rate and storage capacity requirement for transferring the averaged data to an analysis and storage device for long-term storage.

High-performance digital signal averager

A method for improving the speed of convergence to sub-least-significant-bit accuracy and precision in a digital signal averager when the measurements are averaged over many samples where the noise inherent in the signal is not large compared to 1 LSB. A slider offset circuit implements the method which adds offsets to an analog input signal acquired from an analog sensor. The slider offset circuit compensates for limitations in the resolution of an analog-to-digital converter by adding a sub-least-significant-bit offset to the input signal. Similarly, the slider offset circuit compensates for the differential non-linearity using a Gatti offset which are whole number multiples of the average voltage bin width. Speed of convergence to sub-LSB accuracy is further improved by employing non-consecutive increments in the two sliders.

Apparatus for improvement of the speed of convergence to

A method and apparatus for compression and filtering of data associated with spectrometry. The method and apparatus serves to recognize peak events and filter data associated with background noise, thereby reducing the volume of data to be transferred to storage and the data transfer rate required for storing the desired data. The method of the present invention monitors the value of each data point as it is encountered and compares it to the previously encountered data to determine whether it is on or very near a peak. The y values for each data point are continuously summed and averaged to determine the average background level. The deviation .delta..sub.i is determined for each subsequent data point and is used to determine a threshold. Each subsequent data point is compared to the threshold and, if found to be above the threshold, is assumed to be part of or very near a peak. At this point, the averaging is stopped until a subsequent data point is determined to be below the threshold. After any peaks have been detected, all or a portion of the data associated the background noise and scatter in the spectrum may be discarded, with only the data relevant to the peaks, and any other desired data kept. Other desired data may include data associated with background noise close to each peak, every n.sup.th data point, the first group of data points encountered, and data corresponding to the first and last groups of data points in each block of data. The sensitivity may be varied to raise the threshold with respect to the average background level and eliminate errant background noise from appearing as a peak.

Method and apparatus for compression and filtering of data associated

A digital gated base line restorer system for an ionizing radiation spectroscopy device includes a gated base line restorer circuit, responsive to pulses passing through the device, for generating a weighted average of previous base line sample points and applying it to the pulses to compensate for base line offset errors; and a control circuit responsive to the pulses passing through the device, to enable the gated base line restorer circuit to generate the weighted average during intervals between the pulses and applying it during the random pulses.

Gated base line restorer system

An automatic pole-zero adjustment circuit for an ionizing radiation spectroscopy system includes a digital conversion circuit, responsive to random analog pulses passing through the system for converting the random analog pulses to digital pulses; a programmable digital shaping filter including means for applying a pole-zero cancellation adjustment to compensate for under/overshoot at the output of the programmable digital shaping filter; digitally programmable sampling means including means for defining a window for sampling the trailing edge of the digital pulses and means for sampling the digital pulses during that window to determine the presence of undershoot or overshoot; and a digitally programmable control circuit, responsive to the pole-zero sampling means, for driving the programmable digital shaping filter to introduce an under/overshoot correction signal to the digital programmable shaping filter.

Automatic pole zero adjustment circuit for an ionizing radiation

An automatic pulse top optimization circuit for an ionizing radiation spectroscopy system includes a conversion circuit, responsive to random analog input pulses passing through the system, for converting the random analog pulses to digital pulses; a programmable shaping filter, responsive to the digital pulses, for producing an output of predetermined shape which maximizes the precision and accuracy of the anticipated measurement; pulse shape sampling means including means for defining a window for sampling the top of the pulse and means for sampling the pulses during that window to determine the presence of a deviation from the predetermined shape; and a control circuit, responsive to the pulse shaped sampling means, for programming the programmable shaping filter to compensate for a deviation in the predetermined shape.

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Knoxville, TN, United States of America

Russell D Bingham