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DDM (Digit Digital Multimeter) ... what do I need to know?

RobAinscough

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I have some projects lined up that are PC hardware related (Motherboard and CPU and GPU voltages over time). I'm looking to invest in a good quality DDM that can log voltage data at a fairly high sample rate. The two units I'm looking at are:

Siglent SDM3055 5.5 and Siglent SDM3045X 4-1/2 ... to be honest I'm not sure what the difference is other than one costs about $60 more? Will either of these units be sufficient to log CPU vCore, vDIMM, etc. voltage over time?

Cheers, Rob.
 

danadakk

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Can you describe your desired resolution, sample rate, channels needed you are looking for ?
Do you want simultaneous sampling all channels or sequential ?

Regards, Dana.
 

RobAinscough

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Hi Dana,

My desired resolution is something better than software monitoring tools that typically cap out at 100ms (10Hz) ... so anything better than 10Hz. Unfortunately I don't know how quickly VRMs can modulate based on CPU load driver (ms, ns, etc.)? I'm trying to capture under/over voltage compensation that could potentially be a source of CPU/GPU instability.

Simultaneous would be a plus but I can live with sequential (just more time consuming on the testing side) ... depends on the cost to get simultaneous.

Cheers, Rob.
 

danadakk

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Most of the transient is handled by bulk caps, paper seems to imply uS
kinds of VRM response needed. I would bet Intel has a handbook or guide
you may be able to find on their web site discussing requirements.

If you google "motherboard vrm transient response" several videos discussing
this.

If you have to sample low uS kinds of transients to capture then you are looking
at a much faster A/D. And measurements should be differential. Scopes use both
real time and equivalent time sampling to achieve BW. The latter a reconstruction
technique .



Regards, Dana.
 

RobAinscough

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Thanks again, sounds like neither of the DDMs will help, but was interesting to note from some of the video's I watched they do work in the "5.5" realm of accuracy vs. "4-1/2".

Doesn't sound like my Siglent 1104X-E scope will be sufficient either.

Cheers, Rob.
 

danadakk

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If you have to build something up consider starting with high speed
DAQ -


Modern wideband scopes of course have giga sample samplers, multi
channels, and lots of memory to capture an event.....And sophisticated
triggering capability to discern specifc events you want to examine.
Single shot capabiulity to record/store an event for further study. And
ability to move data into a PC environment for further work and documen-
tation.

Regards, Dana.
 
Last edited:

KlausST

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Hi,

Never heard about DDM.
I know DMMs (digital multimeter)

When you say "digit digital multimeter" .. it misses some information: how much digits.
There are 4 digit multimeters with a disply range of 0...9999. Often with +/- polarity.
(3 1/2 digit --> range 0...1999, 6 digit --> range 0...999999)
These DMM often are driven with dual slope ADC. They are slow.

Others are driven with binary working ADCs like SAR ADCs, flash ADCs, sigma delta ADCs.
There range is limited by the number of bits and thus is 0...2^b -1. For example 0...65535 for a 16 bit ADC.

The difference is that the ones often have a decimally limited range where the others have a binary limited range.
Dual slope types (decimal range) rarely have a PC interface.

I recommend to read through some datasheets to get an idea of what is available and what you need.
Maybe a high resolution cope is useful, maybe a PC scope (withput own screen), maybe any other data acquisition system...

Klaus
 

RobAinscough

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Hi Klaus,

Oops, sorry DMM.

I actually went ahead and purchased the Siglent 3055 DMM (5.5) as I still need a good basic DMM for other projects.

I was however disappointed in the EasyDMM software on the PC side. When connected via LAN and I have the 3055 set to "Fast" mode which is supposed to be 150 "readings" per second ... but when I record with EasyDMM I'm getting about 13-14 data points per second. I haven't checked recording direct to a USB stick plugged into the 3055 yet.

For my original question/desire, Dana pointed me in a direction in regards to Transient Response/VRM here:

Asus appear to be using a Scope (Tektronix DPO 7104 along with some probe interfaces) that's most likely outside my budget (see the 10 min mark in that video) even if they are "on sale" at $9,995 cut down from $22,300.

Cheers, Rob.
 

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