How to correctly measure a mixed low&high current
Hi there!
Im trying to determine the consumtion rates of a module Im testing. Particularly it's a Decawave DWM1001 module, which is expected to use around nanoamps during normal state so a LiFePo4 battery should last months
This module has peak spikes of around 100mA once a second, while the TX module is active, and then goes to sleep for the rest of the time (this is when the uA rates are expected)
But I'm having issues to measure this current.
1.-Using a multimeter. Obviously all I see is values jumping all the time, as this is not expected to measure such a unstable current
2.-Using my Rigol DS1052E oscilloscope. For this I use a 0R22 shunt in series with the battery.
When I disable the Low Power mode, I measure 4-5mV (avg, with higher spikes) which is actually the expected 15-20mA current (shunt=0.22 so current is voltage * 4.5)
But when I enable Low Power mode, which is what I actually need to measure in detail, voltage gets down to ~1mv, which means 4-5mA, not reasonable. Then I disconnect the battery from the module and I keep reading the same average voltage!!! ~1mv.
What is worse...Then I plug my probe tip to the Rigol ground test lead, and it keeps reading 800-1200nV...WHY??
I tried an auto-recalibration in the Rigol Tools menu, which ended correctly, but I can't correctly measure voltages under 1mV.
Is this normal? Is this expected from this scope.
Anyway, this is what I have. What other options do I have to fairly-decently measure a current in the range of nA?
I know I could take a bigger shunt, like 5 Ohm so the read voltage would be bigger and more noticeable by my scope, but in this case, the spikes (100-200mA) would drop the voltage thru the shunt resistor below the acceptable supply and it would reset or erratically fail, during this burst...
Anyone...?? Thanks!!
Im trying to determine the consumtion rates of a module Im testing. Particularly it's a Decawave DWM1001 module, which is expected to use around nanoamps during normal state so a LiFePo4 battery should last months
This module has peak spikes of around 100mA once a second, while the TX module is active, and then goes to sleep for the rest of the time (this is when the uA rates are expected)
But I'm having issues to measure this current.
1.-Using a multimeter. Obviously all I see is values jumping all the time, as this is not expected to measure such a unstable current
2.-Using my Rigol DS1052E oscilloscope. For this I use a 0R22 shunt in series with the battery.
When I disable the Low Power mode, I measure 4-5mV (avg, with higher spikes) which is actually the expected 15-20mA current (shunt=0.22 so current is voltage * 4.5)
But when I enable Low Power mode, which is what I actually need to measure in detail, voltage gets down to ~1mv, which means 4-5mA, not reasonable. Then I disconnect the battery from the module and I keep reading the same average voltage!!! ~1mv.
What is worse...Then I plug my probe tip to the Rigol ground test lead, and it keeps reading 800-1200nV...WHY??
I tried an auto-recalibration in the Rigol Tools menu, which ended correctly, but I can't correctly measure voltages under 1mV.
Is this normal? Is this expected from this scope.
Anyway, this is what I have. What other options do I have to fairly-decently measure a current in the range of nA?
I know I could take a bigger shunt, like 5 Ohm so the read voltage would be bigger and more noticeable by my scope, but in this case, the spikes (100-200mA) would drop the voltage thru the shunt resistor below the acceptable supply and it would reset or erratically fail, during this burst...
Anyone...?? Thanks!!
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