FLUKE 3034625_6003_ENG_A_W 电路图.pdf

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1、 Application Note Data logging on the Fluke 884X with TrendPlot F r o m t h e F l u k e D i g i t a l L i b r a r y w w w . f l u k e . c o m / l i b r a r y Advances in analog and digital technology and consumer demand for better perfor- mance and higher quality are presenting new challenges to res

2、earch, development, and test engineers. Today engineers are designing circuits to tighter tolerances, using precision components and sophisticated circuits to ensure optimum performance and mean time before failure (MTBF). Parameters like short-term stability, drift, and fluctuations are critical va

3、riables required to understand a circuits behavior in either controlled or un-controlled envi- ronments. In some cases, to troubleshoot a device, the engineer may find himself looking for elusive problems like intermittent dropouts or glitches. When tasked to measure these param- eters, the engineer

4、 may have to gather multiple instruments and write custom soft- ware routines to capture and analyze thou- sands of measurement data points. Limitations in traditional precision digi- tal multimeters raise some questions: “If I want to read 100 times per second over four hours, what do I do with all

5、 that data?” “How can I see small changes and still track the overall trend?” The Fluke 884X is the first preci- sion multimeter to offer a simple method of capturing and display- ing measurement changes as small as parts per million in real- time, without time-consuming setup or custom programming.

6、 The Fluke 8845A and 8846A include a TrendPlot function that is essentially a technique for reducing a time-series of measurements into a form that is easy to store and analyze, while still maintaining detail. Thanks to on-board signal processing power and a high-performance analog-to-digital conver

7、ter and graphical display, the Fluke 884X is the first precision 6.5 digit multimeter to offer TrendPlot capability. Methods for trending Sometimes a spot measurement doesnt give the whole picture. Parameters change from instant to instant. Power supplies and current or voltage references may drift

8、over time. Oscillators may change with temperature. Con- nectors may open under tension. RadioFans.CN 收音机爱 好者资料库 2 Fluke Corporation Fluke 884X TrendPlot Changes in environment can lead to unpredictable results. By tak- ing multiple measurements over minutes, hours or days you can quantify these cha

9、nges. Param- eters like dc voltage, dc current, frequency, and resistance can be recorded directly. AC voltage and current can be plotted as rms measurements. Temperature, pressure and humidity can be converted into dc voltages by using the appropriate transducer. In the simplest form of digital rec

10、ording, a series of “snapshot” measurements are taken with a fixed interval in between. In this scenario the instrument takes a single measurement for each interval and stores it in memory. A very short measurement inter- val can catch fast changes, but unfortunately it will use memory quickly. Conv

11、ersely, with more data points it takes more time to write the last data point to memory, affecting the sample interval. Even if you have a very large memory, like a hard drive or flash drive, you still face a daunting task of pouring over vast numbers of measure- ments. High-speed, fixed interval re

12、cording is easy to understand and can be accomplished with relatively simple hardware, but it is usually not practical for log- ging over minutes or hours. The user has to select a reading rate and is forced to compromise. “Do I want to record for a long time or do I want to see fast changes? Why ca

13、nt I do both?” Figure 3. Shows a section of the Fluke 884XA dot matrix graphical display. A minimum and maximum data point is plotted in each column of pixels drawing a TrendPlot across the display. Figure 1. To illustrate how sample rate is proportionate to memory size, this plot example shows 10 s

14、amples recorded at a fixed interval 10 minutes. The shorter the time interval between each sample, the shorter the recorded time span and vice versa. Min/Max recording This technique also stores read- ings at the end of each preset recording interval. But instead of taking just one reading per recor

15、ding interval, the instru- ment takes many high-speed measurements over each interval. Processors within the instrument crunch through the measure- ments and log a minimum (min) and a maximum (max) for each interval. The min and max indi- cate the worst-case, short-dura- tion events, and can be as s

16、hort as a few milliseconds. Graphs from these instruments will often plot min and max on the same graph. Automatic time compres- sion and TrendPlot TrendPlot is a recording tech- nique available in Fluke instru- ments, including the 884X Multimeter. It shows the same detailed data as min/max record-

17、 ing, but it is simple to set up and automatically gives you the best time resolution with the available memory. TrendPlot is a form of min/ max recording in which the meter automatically compresses the timescale each time the trend approaches the end of memory. As the meter starts to run out of mem

18、ory, signal processors quickly go to work. They com- bine adjacent recording intervals into a new min and max. You still get to see the worst-case measurements and the overall trend. And because you choose Figure 2. For each sample interval, a minimum and maximum value is plotted, calculated from a

19、large (buffered memory) sample set captured at higher speed. This captures the major changes while still plotting the overall trend without compromises. Trendplot applications for design validation Powersupplystabilityovertime Verifycircuitdesignspecifications Captureintermittentevents/troubleshooti

20、ng random shut-downs (plot key parameters for critical test points looking for changes that correlate to fluctations) Trendcriticalparameterspertestpointduring climate testing temperature cycle Temperaturecontrolledcrystaloscillatorcircuittests Temperaturemonitoring when to stop the measurement, you

21、 automatically get the best time resolution with the available memory. To set up TrendPlot, simply set up as you would for any measurement. Select a measure- ment function, voltage, current, resistance, temperature or any of the other functions on the 884X. Check to make sure the reading looks right

22、is the resolution OK? Are the leads in the right jacks? Then press the ANALYSE button, select TrendPlot, and hit START. RadioFans.CN 收音机爱 好者资料库 3 Fluke Corporation Fluke 884X TrendPlot When to Trendplot, and when to collect raw data TrendPlot graphically plots a trend of measured values over time. T

23、he Fluke 8845A and 8846A capture and plot values over extended periods of time, starting with a short time span then gradually, through a data compression algorithms, plot the trend of values over extended periods of time. The compression algorithm will always retain and display the max and min valu

24、es, thereby plotting the peak devia- tion of a signal over the entire time span. TrendPlot provides a quick look (graphically) at data of inter- est. It does not provide detailed raw data for download and fur- ther analysis. The user cant set the display resolution for both the vertical and horizont

25、al scaleits a fully automatic function. With the 8846A/45A Trend- Plot, you can plot ac power sup- ply voltage to see if its stable and meets specifications. After an hour or two, you should have enough data for a quick visible check. You can also use this function to see the charg- ing curve on a b

26、attery. But if you want to collect raw data, dont use TrendPlot. Instead, set the 8846A/45A to capture the data into a memory stick and down- load the data into a spreadsheet for more detailed analysis. When to use TrendPlot versus a fast sampling digital oscilloscope The Fluke 8846A 6.5 Digit Pre-

27、cision Multimeter will measure milli or micro volts with an accu- racy unmatched by any other measuring device in its class. To achieve this, the meter employs a multi-ramp integrating analog to digital converter. The benefits of this patented design is that it offers higher resolution up to 100 nan

28、o volts, 0.0024 % accuracy, improved linearity and common mode noise rejection. However, due to the multi slope integration times, the fastest reading rate is several hundred readings per second depending on function, range, and measurement setup conditions. Todays common oscilloscope sample rates c

29、an reach as fast as 2.5 GSa/s or a sample interval as short as 400 pico seconds. At this fast rate, the oscilloscope can only capture very short time spans, as little as 20 nano sec- onds. Also, resolution is limited to the vertical sensitivity typically around 5 mV per division and at a measurement

30、 accuracy of 1.5 %. For those applications that require higher resolution and accuracy, or longer time spans, the precision multimeter with TrendPlot mode is the answer. Tip: You can also log each individual measurement to memory, download into a USB memory stick, and analyze the data on a PC. Remem

31、ber that instead of real-time display data, memory data is compromised. The longer it records, the more it compresses the data (see sidebar). By logging to the memory stick, you can retain higher data resolution. The bitmapped vacuum fluorescent display on 884X allows the instrument to show the plot

32、 without connection to a PC. The trend line can show changes as small as parts per million and can even be seen from a distance. 1. Each plot line represents the max and min values measured over the time period repre- sented by each vertical line. The top of the vertical line is the maximum value me

33、asured and the bottom of the vertical line is the minimum value measured. 2. TrendPlot places a vertical line representing the measured value range for all the mea- surements taken since the previous vertical plot was laid down. The first time slot (one pixel width) sets the vertical axis by making

34、the bottom of the scale equal to the minimum measured value and the top of the scale equal to the maximum measured value in that time period. Depending on the meters resolution and the signals characteristics, there can be from zero to many measurements in one time slot. 3. When the meter has gather

35、ed all the mea- surements for the next time slot, it adjusts the vertical axis to meet the minimum and maximum of the two time slots. The excep- tion to this is when the minimum and maxi- mum are equal. Then the first plot (a single pixel) is placed in the middle of the plot. 4. The horizontal axis

36、scaling depends on a number of highly variable rate/timing fac- tors. The meter takes its best guess at an appropriate time per slot and maintains from the first plot on. When the horizontal axis is compressed, each min/max value on the vertical plot is combined with its neigh- bor plot. So, if plot

37、 one has a max of 5.001 V and a minimum of 4.9992, and the plot that its combined with has a max of 5.000 and a minimum of 4.998, then the result is one vertical plot with a line between 5.001 and 4.998. How TrendPlot works Fluke Corporation PO Box 9090, Everett, WA USA 98206 Fluke Europe B.V. PO Bo

38、x 1186, 5602 BD Eindhoven, The Netherlands For more information call: In the U.S.A. (800) 443-5853 or Fax (425) 446-5116 In Europe/M-East/Africa +31 (0) 40 2675 200 or Fax +31 (0) 40 2675 222 In Canada (800)-36-FLUKE or Fax (905) 890-6866 From other countries +1 (425) 446-5500 or Fax +1 (425) 446-5116 Web access: 2007 Fluke Corporation. All rights reserved. Specifications subject to change without notice. Printed in U.S.A. 4/2007 3034625 A-EN-N Rev A Fluke. Keeping your world up and running. RadioFans.CN 收音机爱 好者资料库