Re: [volt-nuts] HP 3458A SCAL
One of the joys of the 3458 is that at 100kHz and below, you can tell the box to bypass the AC rectifier circuit and directly sample the AC waveform with the ADC and then do all the processing, which yields quite good -- well, very good -- accuracy. Above 100kHz, the system must be used like the majority of DMMs and do an absolute value conversion before ADC and computing the TRMS. So I think your system will provide good results either way at, say 500kHz and below, and the 2MHz and 8MHz flatness will have essentially no affect on either way of processing the signal at lower frequencies.
Dick Moore
On Jun 22, 2010, at 5:00 AM, volt-nuts-request@febo.com wrote:
Message: 6
Date: Mon, 21 Jun 2010 16:02:32 -0600
From: "Greg Burnett" gbusg@comcast.net
Subject: Re: [volt-nuts] HP3458A SCAL hardware
To: "Discussion of precise voltage measurement" volt-nuts@febo.com
Message-ID: 033CE4839C214013B50B9F6639424845@gb02
Content-Type: text/plain; charset="iso-8859-1"
Right. SCAL at 2 and 8 MHz will not affect performance below 100kHz. (The
box self-adjusts its input attenuator audio frequency response during ACAL
AC by adjusting for most-flat response of an internally generated
squarewave.)
----- Original Message -----
From: "Poul-Henning Kamp" phk@phk.freebsd.dk
To: "Discussion of precise voltage measurement" volt-nuts@febo.com
Sent: Monday, June 21, 2010 3:25 PM
Subject: Re: [volt-nuts] HP3458A SCAL hardware
In message A4745DFDC9CB48A0931823828C04651E@gb02, "Greg Burnett" writes:
Incidentally, due to the 3458A's input impedance imperfections as a
function
of high-frequency, I really can't much imagine people using the 3458A AC
mode for measurements above 100kHz anyway.
See, this sort of gets to the heart of my effort: I don't care
about performance above 100kHz, but I have not been able to figure
out from the manual, what impact, if any, the 2MHz and 8MHz
calibrations have at lower frequencies.
If there is no relevant impact, My attenuator method will certainly
work for my purposes.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Dick,
I think the mode you're referring to is its ACV SYNC mode (Synchronously
Sub-sampled Mode) which can be used to measure repetitive AC waveforms from
1Hz to 10MHz.
Here are some excellent articles:
HP Journal April 1989 (Several excellent 3458A articles)
http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1989-04.pdf
Ron Swerleins' 10ppm Accurate Digital AC Measurement Algorithm
http://www.home.agilent.com/upload/cmc_upload/All/Swerleins_Algorithm.pdf
Note: Ron's "God's AC" algorithm uses the 3458A's DCV mode to sample AC
waveforms, and is good for AC waveform frequencies at or below 1kHz.
Best,
Greg
----- Original Message -----
From: "Dick Moore" richiem@hughes.net
To: volt-nuts@febo.com
Sent: Tuesday, June 22, 2010 2:02 PM
Subject: Re: [volt-nuts] HP 3458A SCAL
One of the joys of the 3458 is that at 100kHz and below, you can tell the
box to bypass the AC rectifier circuit and directly sample the AC waveform
with the ADC and then do all the processing, which yields quite good --
well, very good -- accuracy. Above 100kHz, the system must be used like the
majority of DMMs and do an absolute value conversion before ADC and
computing the TRMS. So I think your system will provide good results either
way at, say 500kHz and below, and the 2MHz and 8MHz flatness will have
essentially no affect on either way of processing the signal at lower
frequencies.
Dick Moore
...In case anyone wants to try Swerlein's Algorithm, here's a link to all
the downloads:
http://www.home.agilent.com/agilent/editorial.jspx?cc=US&lc=eng&ckey=235459&id=235459
Greg
----- Original Message -----
From: "Greg Burnett" gbusg@comcast.net
To: "Discussion of precise voltage measurement" volt-nuts@febo.com
Sent: Tuesday, June 22, 2010 4:50 PM
Subject: Re: [volt-nuts] HP 3458A SCAL
Dick,
I think the mode you're referring to is its ACV SYNC mode (Synchronously
Sub-sampled Mode) which can be used to measure repetitive AC waveforms from
1Hz to 10MHz.
Here are some excellent articles:
HP Journal April 1989 (Several excellent 3458A articles)
http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1989-04.pdf
Ron Swerleins' 10ppm Accurate Digital AC Measurement Algorithm
http://www.home.agilent.com/upload/cmc_upload/All/Swerleins_Algorithm.pdf
Note: Ron's "God's AC" algorithm uses the 3458A's DCV mode to sample AC
waveforms, and is good for AC waveform frequencies at or below 1kHz.
Best,
Greg
----- Original Message -----
From: "Dick Moore" richiem@hughes.net
To: volt-nuts@febo.com
Sent: Tuesday, June 22, 2010 2:02 PM
Subject: Re: [volt-nuts] HP 3458A SCAL
One of the joys of the 3458 is that at 100kHz and below, you can tell the
box to bypass the AC rectifier circuit and directly sample the AC waveform
with the ADC and then do all the processing, which yields quite good --
well, very good -- accuracy. Above 100kHz, the system must be used like the
majority of DMMs and do an absolute value conversion before ADC and
computing the TRMS. So I think your system will provide good results either
way at, say 500kHz and below, and the 2MHz and 8MHz flatness will have
essentially no affect on either way of processing the signal at lower
frequencies.
Dick Moore
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