EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: Nermash on July 07, 2011, 12:45:18 pm
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Either my projects are power hogs (my last one uses 150 mA, but it is a web server on a PIC mcu), or generally people rarely use this range?
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I work specifically in low power low voltage. If you run hand held items with batteries of any sort, uA is fairly common. For example, if you measure the power consumption of your DMM, once a gross measurement is made in the mA mode
, the burden voltage will cause more inaccuracy, switching to the uA will improve the accuracy switching to uA give's more resolution, taking the effect of burden voltage into account.
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For example, if you measure the power consumption of your DMM, once a gross measurement is made in the mA mode, the burden voltage will cause more inaccuracy, switching to the uA will improve the accuracy.
How's the higher resistance shunt of the uA range going to reduce the error caused by burden voltage?
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I never cared that much about accuracy in uA .
The most that I would ever care , even for battery consumption tests with AA or AAA,
would be in mA range. (milliAmpere).
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I rarely use microamps readings from a DMM. Milliamps is usually enough for supply currents and so forth, otherwise I usually need nanoamps for measuring sensor currents, and use a purpose built transimpedance amplifier.
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Mostly use uA range when fooling around with multimeters, not much else. I do sometimes measure AC standby current drain in consumer devices but even the greenest of those are in the low milliamp range. BTW my best meter for that is the Tek TX-3. It switches seamlessly from microamps to amperes without the need to reposition the test lead plugs.
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I don't use it very often but my friend Brittany Benzaia would use it several times a day measuring the current draw of low power microcontrollers and the standby current of battery operated devices.
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Fluke 87V specifies its burden voltage as a constant throughout all ranges as V/mA, but other DMM have varying burdens depending on range, with the least being in the uA. Agilent specifies it as V/ohms. Maybe I should have said 'some DMMs ..' so a user should check is DMM to be sure. Both the 1272a and 1252a are specified similarly.
From the 1272a manual, see attached.
The burden voltages are specified at the top of the current range. 1 milliamp of current will generate less burden voltage on the 30 milliamp range (with a shunt resistor of 1 ohm) than on the 3000 microamp range (with a shunt resistor of 100 ohm).
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Thanks ejeffrey and alm, you guys are right, my post isn't right, corrections made.
The burden voltages are specified at the top of the current range. 1 milliamp of current will generate less burden voltage on the 30 milliamp range (with a shunt resistor of 1 ohm) than on the 3000 microamp range (with a shunt resistor of 100 ohm).