optimal configuration of HP 3458A to measure 10k

• #25 Reply
  Posted by Echo88 on 11 Apr, 2018 19:41
• Please take a look a Dr Franks nice summary in a related thread: https://www.eevblog.com/forum/metrology/hp3458a-ocomp-delay-related-problems/msg1464930/#msg1464930
  If you use a setting in which NPLC is greater than 10 NPLC, the 3458A just averages the samples of multiple 10 NPLC measurements. Also delay and OCOMP are used on every 10NPLC, so this leads to such a large measurement time. The APER-command integrates over the whole time instead of doing the mathematical 10NPLC/DELAY/OCOMP-averaging, therefore saving sample time.
  
  Here are a few measurements i did which show the timing on a 3458A:
  
  #OCOMP OFF, Delay default, NPLC 10,AZ OFF -> 0.2s
  #OCOMP OFF, Delay default, NPLC 10,AZ ON -> 0.4s
  #OCOMP OFF, Delay 1, NPLC 10,AZ ON -> 1.4s
  #OCOMP OFF, Delay 2, NPLC 10,AZ ON -> 2.4s
  
  #OCOMP ON, Delay default, NPLC 10, AZ OFF -> 0.4s
  #OCOMP ON, Delay default, NPLC 10,AZ ON -> 0.8s
  #OCOMP ON, Delay 1, NPLC 10,AZ ON -> 2.77s
  #OCOMP ON, Delay 1, NPLC 10,AZ OFF -> 2.38s
  #OCOMP ON, Delay 2, NPLC 10,AZ OFF -> 4.33s
  
  #OCOMP OFF, Delay default, NPLC 100,AZ ON -> 4.05s
  #OCOMP ON, Delay default, NPLC 100,AZ ON -> 8.25s
  #OCOMP ON, Delay 1, NPLC 100,AZ ON -> 27.26s
  
  #OCOMP ON, Delay 1, NPLC 50,AZ ON -> 13.65s
  #OCOMP ON, Delay 1, APER 1,AZ ON -> 5.97s
• #26 Reply
  Posted by voltampere on 11 Apr, 2018 19:55
• Thank you for pointing!
  Should have found that by myself 
  
  That makes sense and your numbers are equal to mine.
  
  But still it doesn´t explain why a query APER? gives an aperture of 0,2 sec after i set 50 NPLC.
  
  Any explanation for it?
  
  
• #27 Reply
  Posted by dl1640 on 11 Apr, 2018 22:18
• I didnt see difference between your 2 sets of cmds, APER is straightforward but it is only settable between 500ns to 1s.
  NPLC 50 is identical to APER 1 in 50Hz system, unless you specify by LFREQ LINE which will set integration time to a actually measured line frequency, dont if it really helps to improve any measurement.
  
  Yes, APER 1 saves time of measurenent than NPLC 50.
  
  
  

  Quote

  If you use a setting in which NPLC is greater than 10 NPLC, the 3458A just averages the samples of multiple 10 NPLC measurements. Also delay and OCOMP are used on every 10NPLC

  
  I set NPLC=50, DELAY=1, measure dc current
  the data update rate is less than 3s, that is the DELAY is not inserted into each 10PLC
  so, 50PLC = average of 10PLC is true and the user manual does say that
  but DELAY is used on each 10PLC, is not true, for all conditions at least
  
  also, if I set 50PLC, the APER? is returned as 200ms, yes it is
• #28 Reply
  Posted by Dr. Frank on 12 Apr, 2018 06:28
• NPLC 50 overrides the APER 1 setting, and splits the continuous 1sec aperture.
  
  As NPLC 50 consists instead of 5 measurements, APER? delivers the 200ms aperture of each NPLC 10 measurement.
  
  I recommend to test a longer DELAY if using NPLC 50 instead of APER 1.
  
  Frank
• #29 Reply
  Posted by aronake on 26 Apr, 2024 17:03
• When making 10K ohm measurements on 3458a, can somehow usage of the guard terminal and guard switch be of any help?