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Old 12-04-2006, 04:38 AM   #1
meniscus
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What do these voltages apply to?


The following output is from lm sensors

Code:
Adapter: ISA adapter
VCore 1: +1.30 V (min = +1.42 V, max = +1.57 V) ALARM
VCore 2: +1.49 V (min = +2.40 V, max = +2.61 V) ALARM
+3.3V: +6.46 V (min = +3.14 V, max = +3.46 V) ALARM
+5V: +4.92 V (min = +4.76 V, max = +5.24 V)
+12V: +12.03 V (min = +11.39 V, max = +12.61 V)
-12V: -19.87 V (min = -12.63 V, max = -11.41 V) ALARM
-5V: -2.56 V (min = -5.26 V, max = -4.77 V) ALARM
Stdby: +5.00 V (min = +4.76 V, max = +5.24 V)
VBat: +3.18 V
fan1: 2909 RPM (min = 0 RPM, div = 16)
fan2: 0 RPM (min = 332 RPM, div = 16)
fan3: 3308 RPM (min = 664 RPM, div = 8)
M/B Temp: +41°C (low = +15°C, high = +40°C) sensor = thermistor
CPU Temp: +46°C (low = +15°C, high = +45°C) sensor = diode
Temp3: +41°C (low = +15°C, high = +45°C) sensor = thermistor
The processor i have is an intel P4 3Ghz 478 package prescott.
What voltages apply to this processor?
Is Vcore1 and Vcore2 the voltages of the north and south bridge?

(Ive asked this question in 2 other forums and got 2 different answers>one guy told me the 12V rails apply the processor and the other told me the Vcore1 and VCore2 apply to it)Who do i believe?
 
Old 12-04-2006, 05:21 AM   #2
weibullguy
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+/-12V to the processor! Do you smell smoke? That would be 24V operating the processor.

Vcore is the processor voltage. A P4 probably operates around 1.3V nominally, but the voltage will vary with current as a microprocessor is a constant power device. The max voltage is probably around 1.5 - 1.6V.

The 5V and 12V is for the "big" stuff in your PC. Fans, hard drives, CD/DVD ROM drives, etc. The 3.3V is for the other integrated circuits on the motherboard.

BTW, lm_sensors is neat but from what I've seen it's not really capable of providing true monitoring. The safe-maximum curves for silicon devices like microprocessors are not simply straight lines. It doesn't appear to me that lm_sensors is able to define rules any more complex than straight-line linear. It also doesn't provide enough parameters to understand what is really going on. Take anything lm_sensors tells you with a grain of salt.

FYI, I'm an electrical engineer, so you'll have to decide whether or not my opinion is the tie-breaker.
 
Old 12-04-2006, 08:02 AM   #3
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Thanks! I know who has been telling me fibs now

What about the temperature readings given by lm-sensors> do they not give a fair indication of processor usage at any 1 instant?
 
Old 12-04-2006, 09:05 AM   #4
weibullguy
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Well, you asked, so now you have to read everything.

Both the temperature and voltage are more indicators of problems that have already occurred rather than impending problems. Obviously as usage increases, more power will be dissipated, and temperatures will increase. However, correlating the temperature of a microprocessor to usage would be difficult at best with the supervisory devices used in PCs. There are several variables that would have to be taken into account. Including the change in accuracy of the device used to measure the temperature. Then, of course, there's the lag between change in usage and change in temperature and change in reported temperature. Even at 3Ghz, things don't happen instantaneously.

The other problem is configuring the sensors to report correctly. For example, your system reports 6.46V for the 3.3V rail. Do you divide by 2 or subtract 3? Get this wrong and you could have a problem for quite awhile before you know it. The only sure fired way to get this right is to know exactly which sensor is being used for each monitored parameter and get the associated technical documents.

Assuming the supervisory circuitry is working correctly, some example of how I would use the output of lm_sensors:
  • If you see temperatures going up, fan speeds are less than max, and fan speeds not increasing, something's probably broken and you need to check it out.
  • If you see voltages acting flakey, your power supply has already failed and you need to shut down your machine and replace the power supply.
  • If you manage to get things configured correctly and you see voltages consistently greater than nominal (e.g., the 6.46V being reported for the 3.3V) and temperatures are high, your power supply is busted.

Keep in mind that a PC is not designed (or allowed) to be used for critical functions. You can't use a PC for life support or safety applications. In devices that perform critical functions, other methods are used during the design to ensure that maximum ratings aren't exceeded. The most common is simply derating the parts that are used. Essentially we (I work in aerospace/defense) use bigger parts than we need. This, of course, increases the cost. PC manufacturers use the part that's just the right size for the job to keep costs low.
 
Old 12-05-2006, 05:52 AM   #5
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Thanks for all that. You ve been very helpful
 
  


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