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Looking for ideas to DIY uA Meter (shunt amplifier)
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MiroS:

--- Quote from: 001 on December 15, 2018, 02:05:16 pm ---
--- Quote from: MiroS on December 15, 2018, 12:23:08 pm --- -

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Thanx
But I see what burden voltage is high, isnt it?

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U722 - 100mV
V640 - 5 or 50 mV depending on selected range
U726 - should be similar to U722, maybe even better than that




001:

--- Quote from: MiroS on December 15, 2018, 09:25:33 pm ---
--- Quote from: 001 on December 15, 2018, 02:05:16 pm ---
--- Quote from: MiroS on December 15, 2018, 12:23:08 pm --- -

--- End quote ---

Thanx
But I see what burden voltage is high, isnt it?

--- End quote ---

U722 - 100mV
V640 - 5 or 50 mV depending on selected range
U726 - should be similar to U722, maybe even better than that

--- End quote ---

Yea
It is WERY high
so idea is to keep burden voltage at regulation range
Rerouter:
If you want zero burden voltage, your pretty much limited to a trans-impedance amplifier, that or use a power supply with remote sense leads to compensate it out,

A trans impedance amplifier sinks or sources current to ensure that the burden voltage is 0, or at least as low as the op amp offset error, the output from the op amp is providing a correction voltage to null out that burden voltage, and measuring that output voltage gives you the measurement of the current.
MiroS:

--- Quote from: 001 on December 16, 2018, 12:29:22 am ---
--- Quote from: MiroS on December 15, 2018, 09:25:33 pm ---
--- Quote from: 001 on December 15, 2018, 02:05:16 pm ---
--- Quote from: MiroS on December 15, 2018, 12:23:08 pm --- -

--- End quote ---

Thanx
But I see what burden voltage is high, isnt it?

--- End quote ---

U722 - 100mV
V640 - 5 or 50 mV depending on selected range
U726 - should be similar to U722, maybe even better than that

--- End quote ---

Yea
It is WERY high
so idea is to keep burden voltage at regulation range

--- End quote ---

Not that high as you will see blow :) See this for U623:

For 60nA - U623 - 0,55mV , uCurrent 10uV*60(nA) = 600uV, so again uCurrent is a bit worst.

For 100uA - U623 - 0,97mV , uCurrent 10uV*100 (uA) = 1000uV=1mV, so again uCurrent is a bit worst.

For 1mA - U623 - 10,5mV , uCurrent 20uV*1 (mA) = 20uV, , this time uCurrent seems to be better, but I would say - for 1mA burden voltage of 10,5mV can have any  meaning if we are talking circuit with 1mA over 200mV, for less voltage this burden voltage will have not have any meaning.

That burgen voltage has significant impact only for HIGH current or some very, very specific sitation or ... if you will take  for  comparition e.g. FK87V which will have burden voltage  100mV for 1mA.


p.s.
I own a few of 'U', I took U623 from the shell incidentaly, if you would some test for others 'U' I can do that one day. U623 is better than other listed earlier Meratronik  'U' metters, for sure other U-metters than U623 will give worst results

David Hess:
National application note 242 has all kinds of interesting current measurement circuits.  I especially like the one shown in figure 11 which has a constant burden voltage at different ranges.
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