Fluke 287 Fluke 287 and 289 Multimeter Users Manual - Page 26

287/289 Users Manual out open lead conditions so the Meter leads can be moved between test points without triggering a display update. Note For temperature measurements, the AutoHold threshold is a percent of 100 degrees. The default AutoHold threshold is 4% of 100 degrees, or 4 degrees Celsius or Fahrenheit. Pressing H while in AutoHold mode, forces the Meter's display to update with the present measurement, just as if a stable measurement had been detected. To set the AutoHOLD Threshold Value, press the softkey labeled Setup to access the setup menu. Using the cursor buttons, move the menu selector next to the menu item labeled Recording and press the softkey labeled Recording to open the recording setup screen. Using the cursor buttons, move the menu selector next to the menu item labeled Event Threshold for AutoHOLD and then press the softkey labeled Edit. Press 7 or 8 to scroll through the AutoHold threshold values. With the desired value selected, press the softkey labeled Close. Measuring Crest Factor Crest factor is a measure of signal distortion and is calculated as a signal's peak value over its rms value. This is an important measurement when looking at power quality issues. The Meter's crest factor function is only available for the ac measurements: Vac, mVac, Aac, mAac, and μAac. With the Meter in one of the ac measurement functions, press the softkey labeled Menu. Next, move the menu selector next to the menu item labeled Peak,CF and press the softkey labeled CF. The 16 crest factor value is displayed in the primary display while the ac measurement appears in the secondary display. Frequency, duty cycle, and pulse width are not allowed during crest factor measurements. Capturing Minimum and Maximum Values The MIN MAX Record mode captures minimum, average, and maximum input values. When the input goes below the recorded minimum value or above the recorded maximum value, the Meter beeps and records the new value. The Meter stores the elapsed time since the recording session was started at the same time. The MIN MAX mode also calculates an average of all readings taken since the MIN MAX mode was activated. This mode is for capturing intermittent readings, recording minimum and maximum readings unattended, or recording readings while equipment operation precludes watching the Meter. The MIN MAX mode is best for recording power supply surges, inrush currents, and finding intermittent failures. Response time is the length of time an input must stay at a new value to be captured as a possible new minimum or maximum value. The Meter has a 100 millisecond MIN MAX response time. For example, a surge lasting 100 milliseconds would be captured but one lasting only 50 milliseconds may not be captured at its actual peak value. See the MIN MAX specification for more information. The true average value displayed is the arithmetic mean of all readings taken since the start of recording (overloads are discarded). The average reading is useful for smoothing out unstable inputs, calculating power consumption, or estimating the percentage of time a circuit is active.