Sign in with
Sign up | Sign in
Your question

Voltage measure how to ?

Last response: in Systems
Share
November 29, 2010 6:47:08 AM

hello guys. I measured the voltage of the +12 rail using software and using a analog multimeter ( since i dont have a digital one )

Results

Lavalys software = 12.93 volts
Sandra Lite = 12.6 volts

Analog multimeter :- very close to 12 V

Why does the two software gives completely two different values ? They get their data from the same source ?

I think its not recommended to measure system voltage levels using software for the reasons quite clearly seen above.

Am i correct guys?

More about : voltage measure

a b B Homebuilt system
November 29, 2010 6:49:03 AM

Were both software apps running at the same time? or one, then the other?
Moto
November 29, 2010 6:50:16 AM

Same time
Related resources
November 29, 2010 6:55:34 AM

Obviously i should accept the analogue multimeter reading here. But why is it that the two software applications gives me two completely wrong values ? What does it suggest ?
a b B Homebuilt system
November 29, 2010 7:13:25 AM

First, its virtually useless to measure precise voltage using a multimeter. The voltage fluctuates, the multimeter is slow to react and its measurements too coarse. The two software products likely measured at different instants in time, though it looks like the same time to you.

Check the voltage measurements over time gathered by the scopes used by those who do thorough psu reviews (Figure 19 etc):

http://www.hardwaresecrets.com/article/Aerocool-E80-600...
a b B Homebuilt system
November 29, 2010 12:16:26 PM

thumbchi3 said:
hello guys. I measured the voltage of the +12 rail using software and using a analog multimeter ( since i dont have a digital one )

Results

Lavalys software = 12.93 volts
Sandra Lite = 12.6 volts

Analog multimeter :- very close to 12 V

Why does the two software gives completely two different values ? They get their data from the same source ?

I think its not recommended to measure system voltage levels using software for the reasons quite clearly seen above.

Am i correct guys?

http://www.motherboards.org/articles/guides/1487_6.html
November 29, 2010 12:34:10 PM

Hey so are you saying that the motherboard reading is more accurate than voltmeter reading ?
November 29, 2010 12:37:55 PM

Hey assume that the voltage fluctuates between 12.93 and 11.07 say. OK then the voltmeter would take it as 12 Volts right ?


But still the motherboard sensor gives the output as 12.93 constant for Lavalys and 12.6 volt constant for Sandra Lite. ( why a constant voltage in this case , definitely its value should vary between 11.07 and 12.93 so that the voltmeter would read 12 volts )

Who can explain this behavior?

Still i believe that the volt meter reading is the correct one in this scenario.
November 29, 2010 11:52:31 PM

any one ?
a c 122 B Homebuilt system
November 30, 2010 1:17:39 AM

Assuming valid instrument calibration (something no one but companies and military seems to take the time and money to do):
A digital meter will have a +/- 1% and +/- 1 digital count error.
A good analog meter (Simpson 270, $240) will have an error of 2 to 3% of full scale reading. An inexpensive meter ($20 - $50) can easily have an error of twice that.
November 30, 2010 12:08:37 PM

hey come on man. Cant you understand what iam talking about. If the voltage fluctuates between x and y then the voltmeter would show a voltage of

= (x+ y )/ 2

The average because the needle would not move at that rate.

So now iam getting 12 volts reading from my multimeter. Who cares i don't want 100 % accuracy. What iam concerned is about how can my motherboard sensor give a constant 12.93 volts reading ? It should obviously also have a lower value than that because the volt meter reads 12 volts. ( it should periodically vary around 12 volts example :- 12.93 and 11.07 )

And also Sandra lite gives me that value as 12.6 volt and its constant.

Why is that ?

Anyone has a good reason ?
a c 122 B Homebuilt system
November 30, 2010 2:19:39 PM

thumbchi3 said:
If the voltage fluctuates between x and y then the voltmeter would show a voltage of

= (x+ y )/ 2

The average because the needle would not move at that rate.

That is true only if the rate of change was constant throughout the range. If, for example, the voltage spent more time at the lower part of the range, the average would be lower.

thumbchi3 said:

So now iam getting 12 volts reading from my multimeter. Who cares i don't want 100 % accuracy.

Actually, yes, you do. You are assuming that, because your voltmeter is reading 12.0 volts, you actually have 12.0 volts present. Assuming a 3% tolerance (that's better than average for an inexpensive meter) on a 20 volt scale, that tolerance is based on the full scale reading. That's +/- 0.6 volts right there. When your analog meter reads 12.0 volts, you actually have somewhere between 11.4 and 12.6 volts present.

thumbchi3 said:

What iam concerned is about how can my motherboard sensor give a constant 12.93 volts reading ?

I am assuming that this reading comes from the BIOS, yes? If so, preboot is the period when there is the smallest and most constant load on the PSU.

thumbchi3 said:

It should obviously also have a lower value than that because the volt meter reads 12 volts. ( it should periodically vary around 12 volts example :- 12.93 and 11.07 )

Discussed above.

thumbchi3 said:

And also Sandra lite gives me that value as 12.6 volt and its constant.
Why is that ?

By the time you are running Sandra Lite, you have booted and loaded the OS. You are pulling more power from the PSU now. The greater load means a slightly lower 12 volt rail. And if you are idling, that load is pretty contant also.
November 30, 2010 10:08:35 PM

man how many times did i mention that Sandra Lite and LavaSys was run at the same time. And at the same time i get two different voltage values.

And hey my multimeter is correct because i measured the output voltage of two laptop power supplies and i got exactly 18.5 volts. So now are you gonna tell me that my laptop power supplies are also wrong ?
November 30, 2010 10:49:05 PM

I installed gigabyte easytune6 and it gives me a constant reading of 12.8 volts.

I get three different readings from three different software app's. ( All were run at the same time )

12.93 lavalys
12.6 sandra Lite
12.8 easytune6

I still beleive that the voltmeter reading is the correct one because it gave me the correct voltage for 2 laptop power supplies as well.
a b B Homebuilt system
December 1, 2010 4:19:41 AM

You've heard the arguments. So as long as you are convinced your multimeter is right, I suppose you should run with that.

!