CPU Diode calibration: Round 2 - Page 3

Since87 · 05-13-2003, 11:57 PM

I can think of one other way which is more likely to work.

Put a small shunt resistor (again, a short wire with Kelvin connections) in series with each of the switching inductors of the Vcore regulators.

Attach a high bandwidth differential amplifier to each of these Kelvin connections to get a signal that gives decent resolution on a scope. Look at all three or four of the amplified signals on a scope, and gauge the current from these signals. These signals are going to be very noisy so it's going to take some interpretation to know what is relevant.

Not going to be that accurate...

Okay, yet another method. Most practical of all.

Just remove the Vcore regulators. Hook a seriously beefy bench supply up in their place. Measure the current coming out of the bench supply. The biggest problem with this (other than finding the supply) is getting the bench supply turned on at the right time. I have no idea what the power sequencing requirements of a PC motherboard are. Probably have to rig something up to get the bench supply switched in at the right time. Hopefully, not too much hardware gets destroyed in the process of getting it right.

[I was supposed to be working on a spreadsheet tonight. It will have to wait.]

pHaestus · 05-13-2003, 11:59 PM

Nor I. Here's the link I was referring to:

http://www17.tomshardware.com/cpu/20...ooler5-03.html

Since87 · 05-14-2003, 12:35 AM

They're doing a variation on the second method I mentioned.

Instead of shunt resistances in series with the inductors of the Vcore regulators, they have loops of wire going through a clamp on current probe.

Accuracy most likely sucks, because of the high frequency 'noise' I mentioned earlier. Clamp on ammeters generally have lousy accuracy anyway. High frequency signals, on top of the DC component that the ammeter is attempting to measure, is not going to help the accuracy any.

Still, it is a way to get some kind of number...

Another issue, is that not all of the power dissipation is going to occur in the CPU itself. Some fraction is going to be dissipated in the Northbridge. This is a wild ass guess, but I wouldn't be surprised if 5% of the Vcore regulator's output power, is dissipated in the Northbridge during very memory intensive operations.

pHaestus · 05-14-2003, 12:41 AM

I ask because I have 3 issues against me at the moment:

1) what is the Real CPU temp
2) what is the REAL power applied to coolers from CPU
3) what are the importance of the secondary cooling paths

I have (1) under control. So 2 unknowns left. I have access to Bill's test data for a liquidCC surge waterblock, and I have all the tools necessary to test it as a function of flow rate and generate CPU die, wb inlet, wb outlet, and baseplate temps. So I can cross correlate to get ONE of the other two unknowns. Pick your poison; I am guessing that the power is easier to determine than the amount of secondary cooling that occurs.

So that is why I was asking so everyone is clear.

Thoughts?

Since87 · 05-14-2003, 12:59 AM

Well, if you chill the water so that the CPU is at the same temperature as the motherboard in the socket area, and you insulate as per a TEC to eliminate convection, secondary paths should at least be substantially reduced.

Running a program that stays in the CPU cache without RAM access will minimize Vcore power dissipation occurring in locations outside the CPU.

It seems to me that the biggest problem by far, is getting a trustworthy current measurement.

Can you identify the manufacturer and part number for the Vcore regulator IC on your motherboard? Maybe looking at the datasheet for it will give me some idea how to measure the current accurately.

pHaestus · 05-14-2003, 01:05 AM

Using an Epox 8K7A+ at the moment, which has the Semtech SC 2422 voltage regulator on it for Vcore:

http://www.semtech.com/pdf/sc2422a.pdf

Weren't you the guy that said he did enough electronics crap at work and didnt want to take it home with him?

I am WAY out of my element here so any help is much appreciated.

Since87 · 05-14-2003, 01:09 AM

Quote:

Originally posted by pHaestus

Weren't you the guy that said he did enough electronics crap at work and didnt want to take it home with him?

LOL

Yes, but it's a lot more fun when all I have to do is think about it and someone else does all the work.

pHaestus · 05-14-2003, 01:18 AM

Well not so sure you are gonna convince me that drilling 462 holes to match up exactly with socket pins is the right sort of work to be doing

Nice try though; I thought seriously about it for a minute or two.

Since87 · 05-14-2003, 01:32 AM

Nah, the way to do it is to get some 0.010 foil, some spray on photoresist, and ferric chloride.

Print a cad drawing of the hole pattern on mylar.

Use the mylar to create a photoresist image on the foil.

Then etch the holes into the foil with the ferric chloride.

Something like that, anyway.

Better living through chemistry.

pHaestus · 05-14-2003, 01:57 AM

While we blue sky, here is some data (taken this time at 1Hz so the x axis is reliable):

Somewhat easier to see the oscillations in temp. Still WIDE variances in FFTs where the FFT size is larger than the cache, eh? Would be interesting to calibrate a Morgan and a Barton (tho I am sadly without a Barton) and see how they differ.

pHaestus · 05-14-2003, 02:26 AM

Ok one last test for tonight:

Still not nearly as tight as CPUBurn but nowhere near as erratic as Prime95. I believe distributed folding is quite ram dependent; I will add another 256mb stick tomorrow and see if it makes any difference.

(Much) more to come

pHaestus · 05-15-2003, 10:00 PM

It takes a surprisingly long time for your CPU to return to ambient temperatures after you shut down the box. Not altogether surprising as the copper heatsink SHOULD become a heat source after the CPU is off. The temp jump at boot tho is almost instantaneous. Article writing up in progress as I type.

Since87 · 05-16-2003, 01:29 AM

I've been beating my head against this current measurement problem all night.

I was actually hoping the THG tester had found a clamp-on that might be able to do the job accurately, but considering that clamp on is a hungarian made device with a maximum frequency spec of 1kHz, I doubt that's the case. You need something with reasonable accuracy up to about 2 MHz to have any confidence of accurate results.

It's looking to me, like the most practical means of getting reasonably accurate results, is a modified version of my second idea. (Shunts in series with the switching inductors.) I can design a little circuit that will put out a DC voltage proportional to the current draw. Let me think about how to do this...

pHaestus · 05-20-2003, 10:21 AM

Tanks Since87; seems like this is the last piece of the puzzle for getting a real cross calibration. I have thought of two more tests that I will do over the week:

Why not set the system up and watch the settling of arctic silver over a couple of days of CPUBurn running? I should have the required resolution.

I have another interesting test that involves extreme motherboard airflow to see how big of an effect that cooling the rest of the mobo's components has upon die temps. This is I suppose another indirect way of looking at the secondary cooling and heat sources. This one I'll start tonight.

Since87 · 05-20-2003, 11:52 AM

Does the software you are using, with the MAX6655 development board, allow you to log the values for the three voltage inputs simultaneously with the temperature?

I was thinking you could monitor Vcore with the Vin3 input of the MAX 6655, and connect a signal proportional to the current draw to Vin2.

You could then take the logged voltage and 'current' measurements, and multiply them together, and then multiply by a scaling factor to get the output power of the Vcore regulator. Accuracy wouldn't be great, because the voltage inputs to the MAX6655 aren't that accurate, but the ability to see how power consumption and temperature track would be cool.

Alternatively, I could design a circuit to just put out a voltage proportional to Watts. (I'm not sure how accurately I can do an analog multiply with a reasonably cheap circuit. I believe about 1% accuracy would be fairly easy to achieve. Better than that is probably reasonably easy with some calibration of the circuit.) This Watts output could then be connected to the MAX6655 and/or a voltmeter if greater accuracy was desired.

pHaestus · 05-20-2003, 12:05 PM

Yes it logs the voltages as well; they have to fall within a defined range I believe for the IC but as long as they do then no problems. Being able to log them simultaneously would be a huge advantage. Good idea!

BaconGrease · 05-20-2003, 12:29 PM

Quote:

Originally posted by pHaestus
Just looked at an individual file; it's definitely some electrical interference of some sort:

That is 60cycle electrical interference from electrical outlets, flourescent lights, computer monitor etc... try turning them off and see if the interference persists. You can also plug into a dedicated ground to help diminish it.

Since87 · 05-20-2003, 12:47 PM

Quote:

Originally posted by BaconGrease
That is 60cycle electrical interference from electrical outlets, flourescent lights, computer monitor etc... try turning them off and see if the interference persists. You can also plug into a dedicated ground to help diminish it.

Didn't really read and pay attention did you?

pHaestus · 05-20-2003, 02:06 PM

Should mention that while testing is in progress that all lights in room are turned off along with the monitor of the testbed PC.

Since87 · 05-20-2003, 03:18 PM

Quote:

Originally posted by pHaestus
Should mention that while testing is in progress that all lights in room are turned off along with the monitor of the testbed PC.

But does it matter if all the lights are turned off etc? If it does, then the measurement results are questionable with a running PC.

Verifying insensitivity to EMI would be worthwhile.

pHaestus · 05-20-2003, 03:22 PM

Well the light I use is a 100W table lamp; I figure it CAN'T be good to have that pointing in the same general location. Same with the monitor. Concerned with the lights and monitors as heat sources rather than EMI specifically. Other than the stir plate (which was a rather extreme case) I have never noticed any other interferences.

pHaestus · 05-22-2003, 12:17 AM

This evening's test was to study the effect of cooling all of the other mobo components and hot spots on CPU temperature. To do this, I took a Comair Rotron 172mm fan (it's a 24VDC fan that I am running at 12VDC but it generates a fair airflow still) and pointed it over the CPU socket, mosfets, and other hot bits in that area. I first let the CPU heat up to equilibrium with CPUBurn High priority and then turned on the fan. Here's the graph:

If I were to plot the raw data, you'd see that the air temperature at the heatsink intake was barely changed at all (it actually rose in temperature, but less than 0.75 C) while the CPU temperature drops dramatically. These are those secondary cooling paths and secondary heat sources that everyone is talking about.

One would expect this effect to be larger with watercooling since there is no longer any airflow at all to cool the hot parts. The magnitude of the effect is probably pretty motherboard specific as well; I have never seen this large of a difference before on my A7V-133 with diode readers.

bigben2k · 05-22-2003, 07:50 AM

Nice! Thanks pHaestus!

Do you think that putting a small neoprene "gasket" around the edge of the CPU, would reduce this effect? (not that it would normally be advisable!)

This is a real temp though, isn't it, so air-assisted watercooling may have some potential, no?

Tons of possibilities with your setup

Les · 05-22-2003, 09:51 AM

Interesting.
For a wb probably would expect a larger effect on the "secondary convective resistance"( Rs ?) .
However would expect this to translate to a smaller change in temp due to the lower "C/W" of the water-sink.Maybe:-

Further work on an un-powered cpu with a hsf and wb(using different coolant temps) maybe revealing.

Since87 · 05-22-2003, 10:00 AM

Quote:

Originally posted by Les

Further work on an un-powered cpu with a hsf and wb(using different coolant temps) maybe revealing.

Good thinking.

05-22-2003, 12:17 AM	#72
pHaestus Big Player Making Big Money Join Date: Aug 2001 Location: irc.lostgeek.com #procooling.com Posts: 4,782	OK check this out This evening's test was to study the effect of cooling all of the other mobo components and hot spots on CPU temperature. To do this, I took a Comair Rotron 172mm fan (it's a 24VDC fan that I am running at 12VDC but it generates a fair airflow still) and pointed it over the CPU socket, mosfets, and other hot bits in that area. I first let the CPU heat up to equilibrium with CPUBurn High priority and then turned on the fan. Here's the graph: If I were to plot the raw data, you'd see that the air temperature at the heatsink intake was barely changed at all (it actually rose in temperature, but less than 0.75 C) while the CPU temperature drops dramatically. These are those secondary cooling paths and secondary heat sources that everyone is talking about. One would expect this effect to be larger with watercooling since there is no longer any airflow at all to cool the hot parts. The magnitude of the effect is probably pretty motherboard specific as well; I have never seen this large of a difference before on my A7V-133 with diode readers. Last edited by pHaestus; 05-22-2003 at 12:22 AM.

05-22-2003, 07:50 AM	#73
bigben2k Responsible for 2% of all the posts here. Join Date: May 2002 Location: Texas, U.S.A. Posts: 8,302	Nice! Thanks pHaestus! Do you think that putting a small neoprene "gasket" around the edge of the CPU, would reduce this effect? (not that it would normally be advisable!) This is a real temp though, isn't it, so air-assisted watercooling may have some potential, no? Tons of possibilities with your setup __________________ WBTA (Water Block Testing Alliance) Nordic Hardware WC 101

05-13-2003, 11:57 PM	#51
Since87 Pro/Guru - Uber Mod Join Date: Sep 2002 Location: Indiana Posts: 834	I can think of one other way which is more likely to work. Put a small shunt resistor (again, a short wire with Kelvin connections) in series with each of the switching inductors of the Vcore regulators. Attach a high bandwidth differential amplifier to each of these Kelvin connections to get a signal that gives decent resolution on a scope. Look at all three or four of the amplified signals on a scope, and gauge the current from these signals. These signals are going to be very noisy so it's going to take some interpretation to know what is relevant. Not going to be that accurate... Okay, yet another method. Most practical of all. Just remove the Vcore regulators. Hook a seriously beefy bench supply up in their place. Measure the current coming out of the bench supply. The biggest problem with this (other than finding the supply) is getting the bench supply turned on at the right time. I have no idea what the power sequencing requirements of a PC motherboard are. Probably have to rig something up to get the bench supply switched in at the right time. Hopefully, not too much hardware gets destroyed in the process of getting it right. [I was supposed to be working on a spreadsheet tonight. It will have to wait.]

05-13-2003, 11:59 PM	#52
pHaestus Big Player Making Big Money Join Date: Aug 2001 Location: irc.lostgeek.com #procooling.com Posts: 4,782	Nor I. Here's the link I was referring to: http://www17.tomshardware.com/cpu/20...ooler5-03.html

05-14-2003, 12:35 AM	#53
Since87 Pro/Guru - Uber Mod Join Date: Sep 2002 Location: Indiana Posts: 834	They're doing a variation on the second method I mentioned. Instead of shunt resistances in series with the inductors of the Vcore regulators, they have loops of wire going through a clamp on current probe. Accuracy most likely sucks, because of the high frequency 'noise' I mentioned earlier. Clamp on ammeters generally have lousy accuracy anyway. High frequency signals, on top of the DC component that the ammeter is attempting to measure, is not going to help the accuracy any. Still, it is a way to get some kind of number... Another issue, is that not all of the power dissipation is going to occur in the CPU itself. Some fraction is going to be dissipated in the Northbridge. This is a wild ass guess, but I wouldn't be surprised if 5% of the Vcore regulator's output power, is dissipated in the Northbridge during very memory intensive operations.

05-14-2003, 12:41 AM	#54
pHaestus Big Player Making Big Money Join Date: Aug 2001 Location: irc.lostgeek.com #procooling.com Posts: 4,782	I ask because I have 3 issues against me at the moment: 1) what is the Real CPU temp 2) what is the REAL power applied to coolers from CPU 3) what are the importance of the secondary cooling paths I have (1) under control. So 2 unknowns left. I have access to Bill's test data for a liquidCC surge waterblock, and I have all the tools necessary to test it as a function of flow rate and generate CPU die, wb inlet, wb outlet, and baseplate temps. So I can cross correlate to get ONE of the other two unknowns. Pick your poison; I am guessing that the power is easier to determine than the amount of secondary cooling that occurs. So that is why I was asking so everyone is clear. Thoughts?

05-14-2003, 12:59 AM	#55
Since87 Pro/Guru - Uber Mod Join Date: Sep 2002 Location: Indiana Posts: 834	Well, if you chill the water so that the CPU is at the same temperature as the motherboard in the socket area, and you insulate as per a TEC to eliminate convection, secondary paths should at least be substantially reduced. Running a program that stays in the CPU cache without RAM access will minimize Vcore power dissipation occurring in locations outside the CPU. It seems to me that the biggest problem by far, is getting a trustworthy current measurement. Can you identify the manufacturer and part number for the Vcore regulator IC on your motherboard? Maybe looking at the datasheet for it will give me some idea how to measure the current accurately.

05-14-2003, 01:05 AM	#56
pHaestus Big Player Making Big Money Join Date: Aug 2001 Location: irc.lostgeek.com #procooling.com Posts: 4,782	Using an Epox 8K7A+ at the moment, which has the Semtech SC 2422 voltage regulator on it for Vcore: http://www.semtech.com/pdf/sc2422a.pdf Weren't you the guy that said he did enough electronics crap at work and didnt want to take it home with him? I am WAY out of my element here so any help is much appreciated.

05-14-2003, 01:18 AM	#58
pHaestus Big Player Making Big Money Join Date: Aug 2001 Location: irc.lostgeek.com #procooling.com Posts: 4,782	Well not so sure you are gonna convince me that drilling 462 holes to match up exactly with socket pins is the right sort of work to be doing Nice try though; I thought seriously about it for a minute or two.

05-14-2003, 01:32 AM	#59
Since87 Pro/Guru - Uber Mod Join Date: Sep 2002 Location: Indiana Posts: 834	Nah, the way to do it is to get some 0.010 foil, some spray on photoresist, and ferric chloride. Print a cad drawing of the hole pattern on mylar. Use the mylar to create a photoresist image on the foil. Then etch the holes into the foil with the ferric chloride. Something like that, anyway. Better living through chemistry.

05-14-2003, 01:57 AM	#60
pHaestus Big Player Making Big Money Join Date: Aug 2001 Location: irc.lostgeek.com #procooling.com Posts: 4,782	While we blue sky, here is some data (taken this time at 1Hz so the x axis is reliable): Somewhat easier to see the oscillations in temp. Still WIDE variances in FFTs where the FFT size is larger than the cache, eh? Would be interesting to calibrate a Morgan and a Barton (tho I am sadly without a Barton) and see how they differ.

05-14-2003, 02:26 AM	#61
pHaestus Big Player Making Big Money Join Date: Aug 2001 Location: irc.lostgeek.com #procooling.com Posts: 4,782	Ok one last test for tonight: Still not nearly as tight as CPUBurn but nowhere near as erratic as Prime95. I believe distributed folding is quite ram dependent; I will add another 256mb stick tomorrow and see if it makes any difference. (Much) more to come

05-15-2003, 10:00 PM	#62
pHaestus Big Player Making Big Money Join Date: Aug 2001 Location: irc.lostgeek.com #procooling.com Posts: 4,782	It takes a surprisingly long time for your CPU to return to ambient temperatures after you shut down the box. Not altogether surprising as the copper heatsink SHOULD become a heat source after the CPU is off. The temp jump at boot tho is almost instantaneous. Article writing up in progress as I type.

05-16-2003, 01:29 AM	#63
Since87 Pro/Guru - Uber Mod Join Date: Sep 2002 Location: Indiana Posts: 834	I've been beating my head against this current measurement problem all night. I was actually hoping the THG tester had found a clamp-on that might be able to do the job accurately, but considering that clamp on is a hungarian made device with a maximum frequency spec of 1kHz, I doubt that's the case. You need something with reasonable accuracy up to about 2 MHz to have any confidence of accurate results. It's looking to me, like the most practical means of getting reasonably accurate results, is a modified version of my second idea. (Shunts in series with the switching inductors.) I can design a little circuit that will put out a DC voltage proportional to the current draw. Let me think about how to do this...

05-20-2003, 10:21 AM	#64
pHaestus Big Player Making Big Money Join Date: Aug 2001 Location: irc.lostgeek.com #procooling.com Posts: 4,782	Tanks Since87; seems like this is the last piece of the puzzle for getting a real cross calibration. I have thought of two more tests that I will do over the week: Why not set the system up and watch the settling of arctic silver over a couple of days of CPUBurn running? I should have the required resolution. I have another interesting test that involves extreme motherboard airflow to see how big of an effect that cooling the rest of the mobo's components has upon die temps. This is I suppose another indirect way of looking at the secondary cooling and heat sources. This one I'll start tonight.

05-20-2003, 11:52 AM	#65
Since87 Pro/Guru - Uber Mod Join Date: Sep 2002 Location: Indiana Posts: 834	Does the software you are using, with the MAX6655 development board, allow you to log the values for the three voltage inputs simultaneously with the temperature? I was thinking you could monitor Vcore with the Vin3 input of the MAX 6655, and connect a signal proportional to the current draw to Vin2. You could then take the logged voltage and 'current' measurements, and multiply them together, and then multiply by a scaling factor to get the output power of the Vcore regulator. Accuracy wouldn't be great, because the voltage inputs to the MAX6655 aren't that accurate, but the ability to see how power consumption and temperature track would be cool. Alternatively, I could design a circuit to just put out a voltage proportional to Watts. (I'm not sure how accurately I can do an analog multiply with a reasonably cheap circuit. I believe about 1% accuracy would be fairly easy to achieve. Better than that is probably reasonably easy with some calibration of the circuit.) This Watts output could then be connected to the MAX6655 and/or a voltmeter if greater accuracy was desired.

05-20-2003, 12:05 PM	#66
pHaestus Big Player Making Big Money Join Date: Aug 2001 Location: irc.lostgeek.com #procooling.com Posts: 4,782	Yes it logs the voltages as well; they have to fall within a defined range I believe for the IC but as long as they do then no problems. Being able to log them simultaneously would be a huge advantage. Good idea!

05-20-2003, 02:06 PM	#69
pHaestus Big Player Making Big Money Join Date: Aug 2001 Location: irc.lostgeek.com #procooling.com Posts: 4,782	Should mention that while testing is in progress that all lights in room are turned off along with the monitor of the testbed PC.

05-20-2003, 03:22 PM	#71
pHaestus Big Player Making Big Money Join Date: Aug 2001 Location: irc.lostgeek.com #procooling.com Posts: 4,782	Well the light I use is a 100W table lamp; I figure it CAN'T be good to have that pointing in the same general location. Same with the monitor. Concerned with the lights and monitors as heat sources rather than EMI specifically. Other than the stir plate (which was a rather extreme case) I have never noticed any other interferences.

05-22-2003, 09:51 AM	#74
Les Cooling Savant Join Date: Oct 2001 Location: Wigan UK Posts: 929	Interesting. For a wb probably would expect a larger effect on the "secondary convective resistance"( Rs ?) . However would expect this to translate to a smaller change in temp due to the lower "C/W" of the water-sink.Maybe:- Further work on an un-powered cpu with a hsf and wb(using different coolant temps) maybe revealing.

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