[volt-nuts] HP 3458A SCAL

[Dick Moore]

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 at febo.com wrote:

> 
> 
> Message: 6
> Date: Mon, 21 Jun 2010 16:02:32 -0600
> From: "Greg Burnett" <gbusg at comcast.net>
> Subject: Re: [volt-nuts] HP3458A SCAL hardware
> To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
> Message-ID: <033CE4839C214013B50B9F6639424845 at 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 at phk.freebsd.dk>
> To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
> Sent: Monday, June 21, 2010 3:25 PM
> Subject: Re: [volt-nuts] HP3458A SCAL hardware
> 
> 
> In message <A4745DFDC9CB48A0931823828C04651E at 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 at 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.
>