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Voltage Measurement Methodology

How I Measure the Voltage in My Home

Method After Early January 2018

Automatic voltage logger device, PQL-120.

Beginning in early January, 2018, measurements are taken by an automatic voltage recording device, an AEMC Instruments model PQL-120 power quality logger. 

  • an RMS voltage measurement is taken and recorded every 10 minutes during the day and night;
  • a pause in measurements of between a few minutes and one or two hours occurs each week when data is downloaded and checked and the device is reset;
  • as before, all measurements are taken at the same electrical wall outlet;
  • voltage measurements with this device have been found to be within ±0.2 volts AC of measurements with my digital voltmeters (DVMs) that were used before;
  • the device records voltages to the nearest one-tenth of a volt RMS;
  • data is transferred weekly by computer to a LibreOffice Calc spreadsheet, and results are compiled and reported monthly;
  • averages (means) of all the measurements for each month are calculated to the nearest one-hundredth of a volt RMS.

This automated measurement method is considered much more accurate than the previous manual method as data sets for each month now generally comprise several thousand measurements (instead of only several hundred) taken at regular intervals (instead of irregularly).  There are also no pauses in the taking of measurements due to absences from home, as the PQL device happily takes measurements whether I am present or not.  It even has an internal battery to keep it operating during brief power outages.  The only pauses in measurement taking are once per week while I download the recorded measurements, verify them, and reset the device for the next week. 

Method before January 2018

Digital voltmeter used to test voltage at wall outlet

Beginning in late 2015 and until the fourth week of January 2018, all measurements were taken manually using a digital voltmeter. 

  • measurements have been taken at more or less random times during the day and night (as a light sleeper, it was easy for me to take a few measurements each night, though not as often as during the day);
  • measurements were generally taken less often than once per hour;
  • all measurements were taken at the same electrical wall outlet;
  • all measurements were taken using the same two digital voltmeters (DVMs), a "Kill A Watt" model P4400 power monitor and a BK Precision model 2705B 3½-digit multimeter (pictured);
  • these DVMs have been checked for consistency against my other voltmeters (I have several);
  • voltages were recorded to the nearest one-tenth of a volt;
  • all monthly data was compiled in a WordPerfect Office QuattroPro spreadsheet and treated the same as for other months;
  • averages (means) for each month were calculated to the nearest one-hundredth of a volt, given that data sets for each month generally contain more than two hundred independent measurements.