## Before GA Begins

Naturally we would like to estimate the duration of the QA phase before it begins. But fitting a model to do estimation must wail for testing to begin and for enough data to be collected before an effective stalistical analysis can lie conducted. However, it is possible to use results from pasl projects lo estimate Ihe two model parameters a and k. In preparation for testing a recent software product. Project F, we reviewed the total number of defects discovered during system integration...

## Subsampled AC Algorithm

The algorithm applied internally by the HP 3458A during each subsampled ac measurement is totally invisible to ihe user. The first part of a subsampled ac measurement is autolevel. The input waveform is randomly sampled fur a period of time long enough to get an idea of its minimum and maximum voltage points This time is at leasl one cycle of the lowest expected frequency value (the low-frequency-value of ACBAND). The trigger level is then set to a point midway between the minimum and maximum...

## Effective Bits Irom the DFT

One way to characterize the signal-to-noise ratio of a digitizer is to sample a quiet low-noise and spectrally pure full-scale sine wave and perform a discrete Fourier transform DFT on the resulting data. The dynamic range in dB from the peak of the fundamental to the noise floor of the DFT gives an idea of the low-level signals that can be resolved. The level of ihe noise floor depends on the number of frequency points bins in the DFT, and hence on the number of samples taken, since if the...

## DC Calibration

Calibration of the dc function begins by establishing traceability of the internal voltage reference. The internal 7V Zener reference see A High-Stability Voltage Reference, page 28 is measured relative to an externally applied traceable standard. A traceable value for this internal reference is stored in secure calibration memory until the next external calibration is performed. Next, the gain of the 10V range is determined by measuring the internal 7V reference on this range. The gain value...

## Conclusion

With data collected during system integration testing, we have been able to use a software reliability model to estimate total testing effort and aid in assessing a project's readiness for release to customer shipments. Although the model appears to be somewhat robust to its underlying assumptions, future success will depend upon the integration of customer representative testing techniques into our existing testing process. In addition, there remains the challenge of using the mode to estimate...

## Basic Dual Slope Theory

Dual-slope is a simple integraling-type ADC algorithm. Fig. 1 shows a simple circuit for implementing a dual-slope ADC. The algorithm starts with the integrator at zero volts. This is achieved by shorting the integrator capacitor, C. At time 0 the unknown input voltage Vin is applied to the resistor R by closing switch SW1 for a fixed length of time tu. This portion of the algorithm, in which the unknown input is being integrated, is known as runup. At the end of runup i.e., when SW1 is opened...

## Offset Errors

Linear measurement errors in a DMM are of two general types, offset errors and gain errors. Offset error sources include amplifier offset voltages, leakage current effects Percent of Range Fig. 3. Linearity error as a percent ol reading IR , and thermocouple effects generated by dissimilar metals used in component construction or interconnection. Fig. 5 shows a simplified schematic of the dc measurement function. Switches Si and S2 are used to provide a zero reference during each measurement...

## Software

The HP VXIbus development software runs on HP 9000 Series 200 and 00 Computers Fig. 2 . It is used primarily to verify ihe operation of a VXIbus module. It is also a learning tool for the VXIbus standard. The program set is Fig. 3. The HP 98646A VMEbus Interlace for HP 9000 Series 200 and 300 Computers Fig. 3. The HP 98646A VMEbus Interlace for HP 9000 Series 200 and 300 Computers a combination of callable subroutines written in BASIC. The code is not protected so that users can modify lines to...

## Additional Errors

Gain and offset variations are the dominant sources of measurement error in a DMM. but they are by no means the only sources of error. Measurement errors are also produced by changes in leakage currents in the input signal path. These may be dynamic or quasistatlc leakages. A more complete schematic of the input circuit of the HP 3458A is shown in Fig. 6. Recall that switches SI and S2 Result Vln Vos - lt 0 V05 V, are used to null the dc offsets of amplifier A1 and its input bias current....

## By David A Czenkusch

WITH ITS INTEGRATING analog-to-digital converter ADC capable of making 100,000 conversions per second, the HP 3458A Digital Multimeter DMM raises the possibility that, for the first time, a voltmeter can satisfy many requirements for high-resolution digitizing. What are the characteristics of a high-resolution digitizer Digitizing requires a combination of fast, accurate sampling and precise timing. It also needs a flexible triggering capability. The HP 3458A allows sampling through two...

## Synchronous Subsampling

A thermal converter can measure ac voltages in the frequency band of 20 Hz to 10 MHz writh state-of-the-art accuracy. Sampling rates near 50 MHz are required to measure these same frequencies digitally, but present ADCs that can sample at this rate have far less linearity and stability than is required for state-of-the-art accuracy in the audio band. If the restriction is made that the signal being measured must be repetitive, however, a track-and-hold circuit can be used ahead of a slower ADC...

## Tion

The system external specification can be smoothly translated to the module structure by using the transformation analysis technique provided by SA SD. Transformation analysis enables us to take each data flow diagram and transform it into more detailed data flow diagrams or module structure. By applying this method, we can make a module structure that has a clear correspondence to the system external specification. Proposed Solution for Issue 3. The key elements...

## This mtegratingtype ADC uses multislope runup multislope rundown and a twoinput structure to achieve the required speed

The analog-to-digital converter adcj design for the HP 3458A Digital Multimeter was driven by the state-of-the-art requirements for the system design. For example, autocall brat ion required an ADC with SVi-digit 28-bit resolution and 7 .-digit 25-bit integral linearity, and the digital ac technique see article, page 22 required an ADC capable of making 50,000 readings per second with Ifi-bit resolution. Integrating ADCs have always been known for their ability to make high-resolution...

## By Takeshi Nakajo Katsuhiko Sasabuchi and Tadashi Akiyama

PROBLEMS THAT OCCUR IN SOFTWARE DEVELOPMENT because of human error negatively affect product quality and project productivity- To detect these problems as early as possible and prevent their recurrence, one approach is to identify flaws in present software development methodologies and procedures and recommend changes that will yield long-term defect prevention and process improvement. Typical approaches to software defect prevention have been to Investigate only design methodologies and...

## Internal transfer standards and autocalibration simplify external calibration and extend the period between external

Swerlein, Stephen B. Venzke, and Scott D. Stever ONE OF THE EARLIEST PRODUCT CONCEPTS for the HP 3458A Digital Multimeter was to develop a means for calibrating its measurement accuracies from only two external reference standards. This is not possible with the traditional design for a DMM, which requires independent adjustment of the full-scale gain and zero offset for each measurement range and function, Calibration is a process in which individual gain and offset...

## Waveform Analysis Software

One factor limiting the effectiveness of the HP 3458A as a stand-alone digitizer is the lack of a built-in CRT for waveform display. This shortcoming has been addressed with a software library that turns an HP 3458A and a computer into a real-time single-channel digital oscilloscope and DFT analyzer. The optional waveform analysis library allows a user with an HP 9000 Series 200 or 300 workstation or an IBM PC AT-compatiblecomputer with HP BASIC Language Processor to display waveforms in real...

## Hp A Adc Design

The design of the HP 3458A's ADC is based on these theories for a muitisiope ADC. Decisions had to be made on how to control the ADC. what number base to use, how fast the integrator can be slewed and remain linear, how-much current to force into the integrator i.e the size of the resistors , and many other questions. The decisions were affected by both the high-speed goals and the high-resolution goals. For example, very steep slopes are needed to achieve high speed, but steep slopes cause...

## Dpparlments

The Hewlett-Packard Journal is published bimonthly by the Hewlett-Packard Company to recognize technical contributions made by Hawtati-Packaiti MP personnel While Itie information found In this publication is believed to ha accurate, the Hewlett-Packard Company makes no warranties, express or Implied. 5 to me accuracy or reliability at such information. The Hewlett-Packard Company disclaims all warranties ot merchantability and tlthass for a particular purpose and alt obligations and...

## Precision AC Voltage Measurements Using Digital Sampling Techniques

Instead of traditional DMM techniques such as thermal conversion or analog computation, the HP 3458A DMM measures rms ac voltages by sampling the input signal and computing the rms value digitally in real time. Track-and-hold circuit performance is critical to the accuracy of the method. THE HP 3458A DIGITAL MULTIMETER implements a digital method for the precise measurement of rms ac voltages. A technique similar to that of a modern digitizing oscilloscope is used to sample the input voltage...

## Summary

Two-source calibration of a state-of-the-art digital multimeter provides several benefits Increased process control within the standards labora- Fig. 10. a Using the clock-derived time base, a 100-nV spurious clock signai can lead directly to a WO-fiV error in measuring he internal dc calibration signal, b The HP 345SA uses a random sampling time base mode to eliminate this error source. Fig. 11. a Traditional calibration chain for dc and ac voltage b HP 3458A calibration chain, showing the...

## Data Input Configuration and Measurements

Programming commands coming in over the HP-IB are received and buffered bv an interrupt service routine, which In turn signals the HP-IB parser execution task. The interrupt code is designed to continue reading characters from the HP-IB chip as long as they continue to come in at a rate of 100 is character or faster. In thin manner, an Firmware for the HP 3458A DMM was developed on four HP 9000 Computers Models 320 and 350 under the HP 64000-UX microprocessor development environment Each system...

## Digital AC Input Path

The ac input path provides a wider analog bandwidth and more precise timing than the dc path, The bandwidth of the ac amplifier is 12 MHz on all ranges except the 10-mV and 1000V ranges, where the bandwidth is 2 MHz, Autocalibration guarantees a frequency response flatter than 0.01 0.001 dB throughout the frequency band from 200 Hz to 20 kHz. making this path ideal for characterizing frequency response in the audio band. While the maximum single-shot sample rate of 50,000 samples per second is...

## Multislope Runup

Multislope runup is a modification of dual-slope runup with the purpose of increasing ihe resolution of the ADC. As mentioned earlier, the dual-slope technique s resolution is limited by the maximum voltage swing of the integrator and ihe wideband circuit noise. Multislope runup allows the ADC to have an effective voltage swing much larger than the physical limitations of the integrator circuit hardware. The technique involves periodically adding and subtracting reference charge to or from the...