CPU Diode calibration: Round 2

[pHaestus]

Andrew at Millennium-thermal suggested once that business cards between the heatsink and socket are useful to exclude some secondary cooling paths. It is very close to time to get my wc testbed up and running for some comparisons. I will play around with the air cooling stuff more tonight and tomorrow and then Saturday and Sunday set up a wb.

SO many testing ideas leap to mind. For example, I really wish I had a TBredB and a Barton and a Morgan all to play with (and look at cache and die size effects) but money is a bit tight at the moment for such extraneous consumables. May buy a 1700+ TBredB just for the hell of it though.

I am not exactly sure what you mean with different cooling temps and the heatsink Les. You mean a temp controlled chamber with different ambient temps? I guess I may have to start pricing something like that out if I want to get serious...

[Les]

Originally posted by pHaestus
[B
I am not exactly sure what you mean with different cooling temps and the heatsink Les. You mean a temp controlled chamber with different ambient temps? I guess I may have to start pricing something like that out if I want to get serious... [/b]

Continuing with fannage variation work on hsf (including un-powered cpu)
Fannage on wb (including un-powered cpu)
Then varying temp of coolant in the wb(un-powered cpu).
All exploratory rather than definitive.

Certainly not suggesting expensive equipment.

[pHaestus]

Here is another wacky idea.

What about making an incubator using a plywood box, heat lamps or light bulbs of some sort to generate heat, and then have those connected to dimmer switches to adjust their output. Put the motherboard and system into the box. If my wireless access point can penetrate it then I can skip the monitor, kb, and mouse and just radmin into it to test. Maybe converting an ice chest or styrofoam container would work better than plywood for the wireless. Something like this seems reasonable:

http://www.melodious.com/gate/howto/coop/incubator.htm

I suspect that it would take some fiddling to get right, but I could presumably collect temperatures at a more controlled ambient this way. Just trying to think of ways to get an isothermal environment...

If I can find the stuff to make a decent res for my Little Giant pump I will start setting up a cooling loop tonight. Don't be too surprised if I am testing with the liquidcc surge waterblock for the first few months (it has a hole predrilled for a thermocouple in the baseplate and this same block has been tested extensively by Bill already).

[Les]

A couple of thoughts re The Surge
Although would probably expect the "C/W(TIM)" to scale from the the 100sq mm Die to the 128(?)sq mm CPU would have reservations re the "T/W".
Better "T/W" could maybe expected from the narrower channeled "SlitEdge" ( http://www.overclockers.com/articles748/
However it is probably a little early to worry about such details.

[pHaestus]

one step ahead of you; Bill, Joe Citrella, and I are all getting identical slit edges for cross correlation thanks to Brian at BeCooling

[Les]

A guess at the correlation between Bill's 100sq mm Die and Joe C's 128sq mm Die:


Based on Heat Spreading calculations using guessed relevant Dimensions (not all given in article). Used Bill's "C/W(TIM)"=0.1 and scaled to 0.078125(1/1.28)
for JoeC's(no Spreading).

Looks like it is going to be fun.

EDIT Corrected crappy arithmetic for "C/W(Tim)".

[pHaestus]

OK this is going to require some (much?) more experimental design. I repeated the test as follows: unpowered CPU, no fan --> unpowered CPU + Rotron fan --> boot to CPUBurn with fan--> turn off fan.

Then I got the bright idea that maybe the temperature drop was only due to the increased airflow to the heatsink directly. Made a "roof-shaped" cardboard deflector to put over the 80mm fan. Repeated testing, and now CPU temperatures rise when the Rotron is turned on. This seems to be because the hs/fan's intake air temps also rise when the Rotron is on.

Looks like the important thing here is whether the supply of fresh air to hs/fan is improved or inhibited and not the airflow to the mobo area.

This is not an easy thing to just "test" Maybe a bunch of 40mm fans arranged over all the hot spots would be more useful?

[Les]

Does sound like an experimentalist's field-day.
All results are revealing.
Have corrected crappy arithmetic in previous post.

[Since87]

I've been thinking more about how to measure the current through the switching inductors.

It's turning out to be an uglier problem than I thought at first. The big problem is the resistors to go in series with the inductors.

A length of copper would be great, except for one problem. Copper has a Temperature Coefficient of Resistance (TCR) of 0.4%/C. In other words, unless the copper is kept at a stable temperature, the resistance won't be known and it will cause error in the current measurement. The most practical replacement for copper is probably Nichrome with a TCR of 0.017%/C. However Nichrome has 67 times the resistivity of copper, which means that the shunt resistor would need to be physically large.

Looking through the Digi-Key catalog I found some 0.005 Ohm Nichrome resistors that would do the job. (Ohmite 620HR005) It would take four of these total. Two resistors paralled, in series with each inductor to provide a voltage proportional to the current flow to feed into the rest of the circuit.

The resistors are 1.675" long, and it might be a cramped fit to get them installed, but once the resistors were in place the rest of the circuit could be put in a more convenient location.

So are you up for doing a hack job on your motherboard?

[pHaestus]

Sure. Just set up my Little Giant Pump and reservoir today. Baby steps....baby steps. Hacking up motherboards sounds like much more fun than plumbing though. I think I am about to commandeer a piece of plywood I saw in the garage rafters and just mount all the valves and instruments and tubing on it. That way I can set it up like a table when in use and put it in the corner when not needed.

[BillA]

http://www.intel.com/design/pentium4/guides/252161.htm

3.3.4

anyone know where I can get an unpopulated (bare) P4 mobo ??

and no, I can provide no lead on getting the die

[Since87]

Originally posted by unregistered

anyone know where I can get an unpopulated (bare) P4 mobo ??

Do you have access to one of these TTV's?

Did I miss something, or is Intel actually doing thermal testing with the heatsource distributed uniformly over the whole IHS surface area?

If you can come up with a dead motherboard, I'll strip the necessary components.

[Groth]

I decide to test some of the CPU current measuring concepts on an old socket-7 board. Between it having single phase regulation and being disposable, I figured I couldn't lose.

First problem was the spacing of the toroids's leads. I had a devil of a time heating both at once. Eventually, I melted a big pool of solder onto the board, which conducted enough heat to the loosen the leads simultaneously.

Next difficulty was room. For my shunt I had paralleled five 0.1 Ohm resistors and there simply wasn't enough space between the socket and the nearby capacitors to place the shunt and toroid side by side.

I was forced to mount the resistors vertically, with the inductor on top and a lead returning to the board. Soldering it in was a colossal pain - the extension lead was short enough that the solder would flow at both ends. In the future, I would get some enameled wire and rewind the inductor with long leads.

Next step is amplify and digitize the reading. Last step is to add isolation, for reading from a second PC.

In the meantime, some pointless data! Using CPUburn/BurnK6 launched at high priority, a DMM, and a lot jumper changes. Current scales nicely with both Vcore and multiplier, doesn't it.

[Since87]

Originally posted by Groth
I decide to test some of the CPU current measuring concepts on an old socket-7 board...

...Current scales nicely with both Vcore and multiplier, doesn't it.

Good work.

I'm surprised your DMM did so well with the ripple that must have been there with a single phase supply.

The green line looks a bit off. I'd expect it to split the difference between the other two lines. Still, those are pretty good results.

[Groth]

I'm surprised your DMM did so well with the ripple that must have been there with a single phase supply

Well, there was quite a bit of ripple. The DC reading randomly wandered in a 50-80 mA range, plus a higher frequency 30-40 mA AC component. Lets hear it for eyeball averaging.

Plus, this board was one of the early victims of exploding cap syndrome - the replacement in the regulator has triple the capacitance and half the ESR. Throw in that CPUburn is a steady running program...

The green line looks a bit off. I'd expect it to split the difference between the other two lines. Still, those are pretty good results.

The graph was made with only two significant digits. Give me a few days, and an ADC, and it'll look better. Current vs. time is gonna be sweet.

[Groth]

Prototype done. KX7 soon to get the treatment.

Late for work - details later.

[bigben2k]

I came across an interesting article, and for some reason, I kept thinking about this thread, even though the application described is not the same:

http://www.e-insite.net/tmworld/inde...e=6%2F1%2F2003

I thought it might inspire someone.

[pHaestus]

Would it be possible to get some more detailed info on how this was done Groth? I am guessing that with the nichrome resistors that since87 suggested and your design that I might have something doable?

[Groth]

Do-able, indeed. Actually, the whole thing was fairly easy.

For ye olde K6, I paralleled 5 generic 0.1 Ohm, 3% resistors. For the upcoming KX7 project, I have ten resistors from the same company (Ohmite), but I've chosen the 10 series for their higher precision. Their temp-co isn't as nice the nichrome, so they'll need a fan when doing important work. Depending on what I find when I pull the inductors, I'll use 6 or 9 for the sensing.

A length of twisted pair was attached to the shunt and led to the amplifier stage. I used a TI LF412 dual JFET-input op-amp, half as a unity gain difference amp, half as an inverting amp with a gain of 21. For the Abit board's turn, I'll add another LF412, so that I have 3 difference amps, one for each inductor, and an inverting summing amp with a gain of 75-80 or 110-120.

Next is the isolation stage. I didn't want the reading/recording of date to affect the target computer's workload, so the I passed the amp stage output and a Vcore reading through a pair of ISO124 isolation amplifiers.

Last, but not least, the isolated signals were digitized with a Nat Semi LM87. I used it because it is noise tolerant, easy to interface, and supported by Motherboard Monitor. It only has 8 bit resolution (around 0.2 A resolution for the K7's), but, I already had one in the house.

New brake rotors first; schematics soon.

[Since87]

Sorry to leave you hanging here pHaestus.

Nice work Groth.

Do you know of any good schematic capture shareware? I don't have any good way of creating schematics at home.

I hope you don't mind some suggestions...
Maybe you've thought of some of these things already, but I thought they were worth mentioning just in case.

Originally posted by Groth
I have ten resistors from the same company (Ohmite), but I've chosen the 10 series for their higher precision.

I'd go for minimal TCR. Actual resistance can be measured and compensated for in the following gain stage. Drift due to variations in ambient and airflow can be a real pain.

I don't know what value of shunt resistor you were going for, but keep in mind, the larger the shunt resistor, the more of your Vcore adjustment range you are giving up. On the other hand larger shunt resistors will give better signal to noise ratio.

Originally posted by Groth
A length of twisted pair was attached to the shunt and led to the amplifier stage. I used a TI LF412 dual JFET-input op-amp, half as a unity gain difference amp, half as an inverting amp with a gain of 21. For the Abit board's turn, I'll add another LF412, so that I have 3 difference amps, one for each inductor, and an inverting summing amp with a gain of 75-80 or 110-120.

I'd suggest adding a film 0.1 uF cap in parallel with the shunt resistors. This will bypass a lot of the high frequency transients that come through the capacitance of the switching inductor. These transients might screw up the the amplifier output somewhat, unless the amplifier is fast enough to track them.

I'd suggest using OPA227 Op-Amps. (OPA2227 or OPA4227 for duals or quads) With your present setup (20 mOhm shunt, 9A max current) the input offset voltage of the LF412 can cause a +/-1.7% error in the first difference amp alone. The main advantage the LF412 has is low bias current, and because of the extremely low output impedance of the shunt, bias current is a nonissue. The OPA227 has substantially better: input offset voltage, input voltage noise,
common mode rejection ratio, and unity gain bandwidth.

I can get these at my employer's cost. If you don't mind working with surface mount packages, (SO-8) I'd be happy to send you some. (I might be able to get the dip package in singles.)

I've got more to bring up, but it's late...

[Groth]

Woo hoo, my car stops now. Slide hammer - fun toy.

Do you know of any good schematic capture shareware? I don't have any good way of creating schematics at home.

I've been using LTSpice. Linear puts it out free to encourage the use of their switcher components. It isn't the greatest Spice implementation, nor super for schematics, but the price was right and the learning curve agreeable. I've also been trying to forge my way through the free version Vutrax, with little result.
At home, eh? What packages have you at work? Perhaps they have a cut down share-/free-ware version.

I hope you don't mind some suggestions...

Bring it on...I've more enthusiasm than knowledge and experience.

I'd go for minimal TCR. Actual resistance can be measured and compensated for in the following gain stage. Drift due to variations in ambient and airflow can be a real pain. I don't know what value of shunt resistor you were going for, but keep in mind, the larger the shunt resistor, the more of your Vcore adjustment range you are giving up. On the other hand larger shunt resistors will give better signal to noise ratio.

I lack the equipment to accurately measure resistances below a tenth ohm (&$^%# DMM), making 3% tolerances mighty ugly. Cheap upgrades? I could have fairly wide uncompensated temperature swings with the series 10 before error reached 3%.
On the K6 board, I discovered that the regulator was not compensating for the shunt - the nominal 2.4 V was appearing on the inductor side, not the CPU side. I'd like to think that KX7 has better feedback circuits, but, to be safe, I'll use a shunt in the 0.5 to 1.0 mOhm region. This will also decrease the self-heating and associated drift.

I'd suggest adding a film 0.1 uF cap in parallel with the shunt resistors. This will bypass a lot of the high frequency transients that come through the capacitance of the switching inductor. These transients might screw up the amplifier output somewhat, unless the amplifier is fast enough to track them.

I used a RC low pass filter on each side heading into the difference amp. 1 Mhz corner frequency versus 3 Mhz unity gain bandwidth. I'll add a shunt bypass cap, and see if it anything changes.

I'd suggest using OPA227 Op-Amps. (OPA2227 or OPA4227 for duals or quads) With your present setup (20 mOhm shunt, 9A max current) the input offset voltage of the LF412 can cause a +/-1.7% error in the first difference amp alone. The main advantage the LF412 has is low bias current, and because of the extremely low output impedance of the shunt, bias current is a nonissue. The OPA227 has substantially better: input offset voltage, input voltage noise, common mode rejection ratio, and unity gain bandwidth.

A case of using what I had in stock. As for the input offset voltage, a bit of hand trimming while using known inputs killed it. Power supply noise/regualtion was problem; cured with 10V zeners and filter caps.
I'm more than willing to pop some OPA227s in to compare performance. If nothing else, I'd be a fool to turn down parts at bulk prices. Surface mount is wonderful, saves tedious drilling.

[Groth]

This is what I used for the difference stage. I actually used a 200 Ohm trimmer in series with a 9.9k resistor where it shows the 10k's. With precision resistors/amps, you could get away without the timming. Plus I'm just lazy with the drawing...

[Since87]

Originally posted by Groth
I've been using LTSpice.

I'll check it out. I use Orcad at work. There is a "student" version that's downloadable but it's extremely limited, and would be unethical for me to use anyway due to the 'student use only' language.

Bring it on...I've more enthusiasm than knowledge and experience.

Great, I've got more knowledge and experience than enthusiasm. Maybe if pHaestus has more money than brains, the three of us can get something pretty cool put together.

Actually, it sounds like your general electronics knowledge is very good. I've been working for a power measurement instrumentation company for the last 10 years. I've got too much experience at this for it to be much fun, but I want to see more graphs out of pHaestus, so I'll put the effort in.

Perhaps the three of us could do something like:

Groth and I work out a design that produces a voltage output scaled for use with the MAX6655's 3.3V A/D input. (Need an accuracy target. I'd suggest +/-1% max from 10C to 50C. The MAX6655 will add +/-1.5%.)

pHaestus pays for the parts to build two of these. One for himself and one for Groth.

Groth builds the two circuits.

I calibrate the two circuits, and do any mods required to get them in spec. (I'll even temp chamber test them.)

Are you two interested in an arrangement along these lines?

[pHaestus]

How many bananas are we talking about for parts?

[Since87]

Originally posted by Groth
This is what I used for the difference stage. I actually used a 200 Ohm trimmer in series with a 9.9k resistor where it shows the 10k's. With precision resistors/amps, you could get away without the timming. Plus I'm just lazy with the drawing...

I'd suggest the circuit below. (Largely because I have access to laser trimmed 20K center tapped resistor networks, with very good ratio accuracy and ratio tempco specs. I like to avoid trimming as well.)

I think it would be a good idea to up the capacitance to roll off at 10kHz. (or even lower depending on the A/D used) It's a good idea to filter out the current ripple as soon as possible.

I'd also swap the two input signals to put the 'noisier' signal into the noninverting input. (The way I've redrawn the circuit, the noninverting input will do a better job of filtering at high frequency because the cap goes to ground rather than the output. The amp will have a significant output impedance at high frequencies.)

Anyway, once again it's late. I hope I'm actually making sense. Enough for tonight.