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??? 07/11/09 13:14 Read: times	#167076 - It is parallel like your second scheme. Responding to: ???'s previous message

List of 85 messages in thread

Topic	Author	Date
Calibrating resistors using AT89C51RD2		01/01/70 00:00
The problem is not manufacturing tolerances...		01/01/70 00:00
those low drift 0.01% resistors are too expensive.		01/01/70 00:00
Now, that you enter into a discussion...		01/01/70 00:00
more details		01/01/70 00:00
Drift is well documented		01/01/70 00:00
No longer published in todays datasheets...		01/01/70 00:00
thanks that was very useful		01/01/70 00:00
You can't calibrate without a reference!		01/01/70 00:00
I have a Hioki DMM as a reference		01/01/70 00:00
But you said auto-calibration		01/01/70 00:00
No		01/01/70 00:00
Need lots of bits		01/01/70 00:00
good analysis		01/01/70 00:00
what design?		01/01/70 00:00
how precise is that?		01/01/70 00:00
50000 counts		01/01/70 00:00
you are making the usual mistake of ....		01/01/70 00:00
not just more precise, but lower drift as well		01/01/70 00:00
Calibration		01/01/70 00:00
can I regularly calibrate?		01/01/70 00:00
many issues involved		01/01/70 00:00
Then...		01/01/70 00:00
Assuming and supposing...		01/01/70 00:00
Ok...		01/01/70 00:00
How fast? How many bits? How stable input signal?		01/01/70 00:00
more details		01/01/70 00:00
More details needed...		01/01/70 00:00
spikes of source could be a problem		01/01/70 00:00
Hhm...		01/01/70 00:00
Hard to self-calibrate		01/01/70 00:00
high sampling rate is not for calibration		01/01/70 00:00
It is a constant current source		01/01/70 00:00
Answers and questions...		01/01/70 00:00
Answers		01/01/70 00:00
Oh, I think I know what it is...		01/01/70 00:00
That's true		01/01/70 00:00
Difficult!		01/01/70 00:00
since this is about calibrating known resistors ....		01/01/70 00:00
Too fast for manual change		01/01/70 00:00
My solution		01/01/70 00:00
I have seen nothing yet that gives ....		01/01/70 00:00
How?		01/01/70 00:00
two screw terminals and a precision resistor		01/01/70 00:00
What are exactly the shunts you switch?		01/01/70 00:00
currently ...		01/01/70 00:00
You should test...		01/01/70 00:00
good idea...		01/01/70 00:00
Well, I suspect...		01/01/70 00:00
don't expect		01/01/70 00:00
A look into datasheet is always important...		01/01/70 00:00
Both problems		01/01/70 00:00
Advantages of shunts in series		01/01/70 00:00
Current scheme...		01/01/70 00:00
How make before break?		01/01/70 00:00
It is parallel like your second scheme.		01/01/70 00:00
Offset voltages?		01/01/70 00:00
Yes		01/01/70 00:00
Try the following...		01/01/70 00:00
Wht's the difference?		01/01/70 00:00
You should, to find out what's wrong!		01/01/70 00:00
Ok but Isn't it easier to calibrate?		01/01/70 00:00
Yes, but...		01/01/70 00:00
Purpose of auto calibration		01/01/70 00:00
No!		01/01/70 00:00
Did you think about the shunt error during the "make"?		01/01/70 00:00
disadvantages of series scheme		01/01/70 00:00
Not really...		01/01/70 00:00
0.1%		01/01/70 00:00
Surprise!		01/01/70 00:00
voltage drop		01/01/70 00:00
So low?		01/01/70 00:00
momma! I want it all, but refuse to pay		01/01/70 00:00
Wanting to achive a precision of 0.01%...		01/01/70 00:00
next he will make a perpetuum mobile		01/01/70 00:00
how true and ...		01/01/70 00:00
Precise enough		01/01/70 00:00
that MAY be true for VOLTS		01/01/70 00:00
OK, give me a few days time....		01/01/70 00:00
Try to avoid it at all!		01/01/70 00:00
You need a lot of individual precision for 0.1% all-range		01/01/70 00:00
Owens		01/01/70 00:00
Yes		01/01/70 00:00
Good discussion but...		01/01/70 00:00
a hypothetical example		01/01/70 00:00

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