Author Topic: Microcurrent out of range  (Read 1255 times)

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Offline DavidDLC

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Microcurrent out of range
« on: December 09, 2016, 11:25:11 am »
How Am I know if the microcurrent is out of range ? This question is when I want to measure unknown currents.

What is the microcurrent value for overload ?

I made this just for experiment:

I'm reading a current of 155 uA on the uA range very stable, then I switch to the nano amps range expecting to have the maximum value on  the range which is 1250 nA, but the readings on the voltmeter are fluctuating between  770 and 817 nano amps.

Can somebody explain please ?

David DLC.
 

Offline mzacharias

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Re: Microcurrent out of range
« Reply #1 on: December 10, 2016, 12:05:40 am »
I have no actual experience with the microcurrent but nevertheless I'm willing to suggest that that this is normal operation. Just as any ordinary multimeter uses progressively larger value shunt resistors with a corresponding increase in burden voltage, the microcurrent must play by the same rules, it is merely designed mainly to  minimize these losses where insertion of such a measurement device might upset normal operation of the circuit, mainly an issue with low voltage, relatively high current circuits, 3.3 volts, 2.5. 1.2, etc.
 

Offline DavidDLC

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Re: Microcurrent out of range
« Reply #2 on: December 10, 2016, 05:03:55 am »
Dave, can you comment on this please ?


David DLC
 

Online guenthert

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Re: Microcurrent out of range
« Reply #3 on: December 10, 2016, 05:07:56 am »
In the nano amp range the u-current uses a moderately large 10 kOhm shunt resistor.  This seems to be large enough to allow EMI picked up via the leads to have a significant effect.  Try shielding the leads and the u-current or otherwise minimizing EMI (at my place Ethernet-over-powerline, a.k.a. HomePlug, causes quite some grieve).

Generally speaking though, you might want to avoid driving measurement instruments outside their specifications.
 

Offline wraper

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Re: Microcurrent out of range
« Reply #4 on: December 10, 2016, 05:36:56 am »
https://www.eevblog.com/projects/ucurrent/
So unless output voltage does not exceed specified range (1.25V), it shouldn't be overloaded (if there is DC on the input).
Quote
Specifications – µCurrent™ GOLD

3 Current ranges:
+/- 0-1250mA (20µV / mA burden voltage typical) * switch contact resistance plays a role here. 10uV due to the shunt resistor.
+/- 0-1250µA (10µV / uA burden voltage)
+/- 0-1250nA (10µV / nA burden voltage)
NOTE: Higher currents are available by increasing the battery voltage, to a maximum of 5.5V, which would give +/-2250mA/2250µA/2250nA maximum)
Output Voltage Units:
1mV/mA
1mV/µA
1mV/nA
NOTE: You simply read your mV multimeter range as if it were mA/µA/nA
Resolution (nA range): 100pA (3.5digit meter), 10pA (4.5 digit meter), 1pA (5.5 digit meter)
Accuracy (typical): <+/-0.05% on µA and nA ranges, <+/-0.1% on mA range.
Output Offset Voltage: <50µV (essentially insignificant on 4.5 digit meter)
Bandwidth: >300KHz (-3dB)
Temperature Drift: <10ppm / degC (µA/nA), <15ppm / degC (mA)
Noise: < -90dBV
THD: < -60dB
Battery: CR2032 Lithium coin cell (optional 3 x AAA’s)
Battery Life: >50 hours (battery good LED ensures accurate measurement when LED is on). 2.65V cutout voltage.
« Last Edit: December 10, 2016, 05:45:48 am by wraper »
 

Offline DavidDLC

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Re: Microcurrent out of range
« Reply #5 on: December 10, 2016, 06:10:21 am »
Generally speaking though, you might want to avoid driving measurement instruments outside their specifications.

I know that, my original comment was in the case you are measuring an unknown current.

David DLC.
 


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