accurately measuring integrated power consumption

What's a good instrument (need make & model number) to measure the integrated power consumption of my complex micro-controller controlled bee-hive monitor? It rapidly goes in and out of multiple modes, turns 74 sensors on/off, pulses LEDs to 50mA, draws 65mA to heat micro-miniature hot plates, etc. Average current is from 0.5 to 3mA, but is hard to measure. It spends much of its time drawing microamps, and this must also be accurately integrated over time.

Going through my considerable collection of smart, highly-capable instruments, there's not one that will make continuous, accurate integrated-current power-consumption measurements. The closest are awesome 6.5-digit bench multimeters, that can be set to measurement integration times of 100 PLC (about 1.6 seconds), but these are discontinuous measurements, with gaps, not suited for the job.

Yes, there are fuel-gauge ICs available, but we need to purchase an instrument, with a wide dynamic range / peak handling capability, plug it in, and take readings, so we can experiment as we work, programming the beehive-monitor's software.

Not even my new awesome-looking Keysight E36312A data-logging bench supply can do this simple task. The word, "integrate" doesn't appear in the manual. Nor does the word, "average" appear.

OK, I have this little $15 USB stick, with a cute display, that includes a running mA-hr value. If I open it up and do some cut-jump hacking, maybe it could be integrated into my bee-hive monitor's power system. What's its peak-handling capability, who knows. Sheesh!

Maybe my 66321B "Mobile Communications DC Source", although the word, "integrate" doesn't appear in its manual either. OK, it will "average" discrete measurements. Not very re-assuring. It can fill up a buffer with 2048 data points... Arrghh!

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 Thanks, 
    - Win
Reply to
Winfield Hill
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Win, is this something that has to live in the field or on you lab bench.

If it's on the lab bench then some A/D converter that plugs into your computer. Like a labjack.

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George H.

Reply to
George Herold

I forgot to mention LoRa transmitter currents. We'd like to setup the instrument, and make a measurement over a complete cycle of activity.

On the bench. Thanks for the suggestion, George, but with rapidly-changing, and pulsing currents, we need an integrating ADC, rather than SAR type, with millions of samples, some missing the pulses.

--
 Thanks, 
    - Win
Reply to
Winfield Hill

Measuring power in circuits with low frequency crest factors requires filtering of the rms measurement values. Something like a Yokogawa will give a wideband analog power-related output which can be filtered and logged. Data that doesn't filter will risk aliasing and spurious error.

All analog processing adds another layer of tolerance and error - but avoids aliasing, or picket fenceing, which seems to be what you're concerned about.

RL

Reply to
legg

An older Fluke 8922a offers analog output, but is hampered by autoranging, if engaged. Autoranging is likely to be useless when you're looking at LF measurements with large crest factor - the errors of the largest measurement range needed without clipping will dominate the average.

RL

Reply to
legg

On a sunny day (31 May 2019 07:00:23 -0700) it happened Winfield Hill wrote in :

Video FLASH ADC record to disk, process later? Or just add a PIC to that ADC do the processing in real time.

That is how I would do it...

Reply to
Jan Panteltje

Not clear if you need measurements over very short intervals, or just how much it average out over a day. If it's more along the lines of the latter, how about a Kill-a-Watt meter? Depends on how accurate you need it and over what interval.

Reply to
trader4

Is the supply voltage constant? If so you just need to measure average current. Seems like any DVM that you can acquire samples of would work; suck out a string of measurements and average. Maybe lowpass the current sensor to improve your statistics.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
John Larkin

Well just an integrator.. low pass filter. I guess that's obvious, so you must want to see the peak heights too?

GH

Reply to
George Herold

ISTR a flyer from Keysight about dedicated instruments for measuring such PSU currents.

Googling for "dynamic current measurements" yielded

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"The CX3300 series Device Current Waveform Analyzers consists of mainframes and dedicated sensors enabling dynamic current measurements and analyses from 100 pA up to 100 A. It has up to 200 MHz wide bandwidth and 14-bit or 16-bit wide dynamic range. It also enables you to measure dynamic voltage with up to 16-bit resolution.

"For IoT applications, you can measure the current profile of low power device including both sleep and active states with up to 100 dB wide dynamic range, without having to use multiple instruments or make multiple measurements.

"For mobile applications, the wide bandwidth and low noise performance enable current profile measurements of PDN (Power Delivery Network or Power Distribution Network) including both large inrush current and small sleep current with the same instrument."

Reply to
Tom Gardner

You need to borrow a coulometer from an electrochemist :-). Usual mode is to set a constant output voltage and then integrate the current. Some brief googling turned up this general purpose machine as an example:

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No idea of cost but it will do up to 10V output and 100 mA, with 1 MHz bandwidth.

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Regards, 
Carl Ijames
Reply to
Carl

Cheapest and fastest would be an eval board for one of numerous coulomb cou nter ICs. They all seem to use a voltage-frequency-converter (VFC) with eac h pulse representing a discrete unit of charge, intended to interrupt an ex ternal uC for counting. The eval board software looks good, time stamping t he VFC pulses, storing, displaying a running total, communicating with the board via USB. Th most expensive component required is a cheap laptop. The coulomb counters seem to be limited to around 60dB dynamic range.

Reply to
bloggs.fredbloggs.fred

Power it from a supercap and measure the before and after voltages!

Ones that I tried had self-discharge time constants of months.

--
John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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Reply to
John Larkin

Sounds good, have a part number, to get me started?

--
 Thanks, 
    - Win
Reply to
Winfield Hill

The eval board and software for the DS2740K looks like the simplest and most self-contained, but as usual Maxim fails on ordering information. Analog sells the eval board for their LTC4150 as p/n DC756 in stock at $50, but it's an I2C interface requiring a DC590B USB contoller for another $50 with no availability until July.

Reply to
bloggs.fredbloggs.fred

You can use the Silabs evaluation board energy profiler:

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Cheers

Klaus

Reply to
Klaus Kragelund

This one seems more advanced and easier to use with any target:

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Cheers

Klaus

Reply to
Klaus Kragelund

What's wrong with the coulomb meter in the book?

Reply to
Tom Del Rosso

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  When I tried casting out nines I made a hash of it.
Reply to
Jasen Betts

You don't need a coulomb meter, use 2 electrodes in suitable solution. Yes, it's old school wetware, but you've probably got the bits in stock & can do it now.

NT

Reply to
tabbypurr

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