THD measurement procedure for Keithley 2015 THD - Page 1
Forum section: electronics / testgear

author: diydidi
author_rank: Contributor
timestamp: May 05, 2016, 06:18:00 pm
content: Can anyone give me some step by step instuctions to do THD measurements with this piece of gear.I would like to be able to do this from the panel buttons only and not via GPIB.Nowhere on the net does anyone explain this. Gery Sweeney comes close, but he isn't returning my mailAny help welcome.

author: jpb
author_rank: Super Contributor
timestamp: May 05, 2016, 08:29:49 pm
content: It is all on page 2-35 of the manual onwards:Select the functionFrom the front panel, select the measurement function by pressing SHIFT then THD.Set the distortion measurement type1. Press THD-MEAS and the display shows "TYPE: THD".2. Use the right cursor to highlight the type selection, then use the  and  keys to selectTHD, THD+N, or SINAD.3. Press ENTER, then press EXIT.Set the distortion frequency acquisitionThe Model 2015 must know the fundamental frequency of the input waveform. Even adifference of a few hertz can cause large errors. The choices are AUTO, SET, and ACQUIRE.AUTO acquires the frequency before each distortion reading. This slows down the reading rate,but it is useful if the source frequency is unknown or unstable. ACQUIRE takes a frequencymeasurement once and uses it for distortion measurements. SET allows you to select a frequencybetween 20 and 20kHz (60Hz is default). AUTO or ACQUIRE are recommended instead of SET,as the programmed frequency of the external source may not be accurate.1. Press THD-MEAS.2. Press ENTER once and the display shows "FREQ: AUTO".3. Use the cursor keys to select AUTO, SET, or ACQUIRE. (The source must be connectedand turned on for ACQUIRE.)4. Press ENTER. If SET was selected, you are prompted for the frequency to be used. Usethe cursor keys and press ENTER to select it.5. Press EXIT.Set number of highest harmonicThis option sets the number (n) of the highest harmonic included in the distortion calculation,where "n" is between 2 and 64 (2 is default). For example, the harmonic with a frequency twicethat of the fundamental is the second harmonic (n=2). This function acts as a brick-wall, lowpassfilter. It has an upper limit of 50kHz or 64 times the fundamental frequency, whichever islower. This option has no effect in the THD+n or SINAD modes.1. Press THD-MEAS.2. Press ENTER until the display shows "UPPR HARM: 02".3. Set the number of the highest harmonic using the cursor keys.4. Press ENTER, then press EXIT.Set measurement unitsFor the THD and THD+n modes, the measurement units can be percent or dB. SINAD isalways displayed as dB.1. Press THD-MEAS.2. Press ENTER until the display shows "UNITS: PERC".3. Select PERC or dB using the cursor keys.4. Press ENTER, then EXIT.Select shaping filterThe Model 2015 has digital shaping filters to simulate having the sample signal pass throughvarious types of telephone lines. The filter is turned off by default (NONE).1. Press THD-MEAS.2. Press ENTER until the display shows "SFIL: NONE".3. Select NONE, C (C message weighting), CCITT, CCIRARM, A (A weighting), or CCIRusing the cursor keys.4. Press ENTER.Set the voltage rangeThe Model 2015 defaults to autoranging for the voltage input range. If you prefer manualranging, use the lowest possible range for the signal level. Not using the appropriate rangecauses inaccurate readings, or the display may show "OVRFLW" or "UDRFLWWhile the 2015 is measuring distortion, press the manual range keys. The display shows thenew range briefly. Press AUTO for autoranging.There is more on measuring harmonics etc.