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====== Current Measurement ======

===== Nordic Power Profiler Kit II =====

[[https://infocenter.nordicsemi.com/pdf/PPK2_User_Guide_v1.0.1.pdf|Manual]]

== Limits ==

  * Max V: 5.5V
  * Max I (measured): 1A
  * Max I (sourced): 600mA

== Accuracy ==

  * < 50mA: ± 10% and ± 2% offset 
  * >= 50mA: ± 15% offset ± 5%

== Qs ==

  * Is it robust to output overcurrent or overvoltage?
  * What does LED mean?

== Log ==

25 April 2024

I connected it to a faulty device which drew too much current. The ppk2 firmware crashed as soon as power was switched on, and the device disconnected from USB. It seems like it does not have any overcurrent protection. A forum post said the sense resistors were damaged by overcurrent, and another suggested that they could be partly damaged and ruin the accuracy. Can it be recalibrated?

== Misc ==

There is a third party python API: [[https://github.com/IRNAS/ppk2-api-python]]

Forum post about using it: [[https://community.element14.com/technologies/test-and-measurement/b/blog/posts/nordic-power-profiler-kit-ii-python-api]]

===== INA3221 =====

  * I2C output, 3 channel amplifier.
  * Max 26V.
  * 350 μA consumption (quiescent though - working unspecified)
  * 13 bit ADC. 40uV resolution on current sense.
  * VSHUNT Shunt voltage input –163.84 to 163.8 mV. Quite limiting.
  * [[https://www.ti.com/tool/download/CS-AMPLIFIER-ERROR-TOOL]]
  * [[https://www.ti.com/lit/ds/symlink/ina3221.pdf]]
  * Supply 2.7V - 5.5V

==== Aliexpress devboard notes ====

  * Rs: 2W, 1%, 100mOhm.
  * Solder jumpers connect a chosen pin to A0 to set I2C address.
  * Voltages are measured from -ve sense pins.
  * VS: Supply voltage
  * VPU: Pullup voltage for power valid function
  * TC: Timing control alert. Used for power sequencing test.
  * Board has 10k i2c pullups

100mR shunts gives max measurable current of 1638mA. I think it shouldn't be damaged with more though - abs max values are all much higher.

{{:ina3221_board.png?600|}}

===== ACS758 =====

Suitable for high current, high or low side, measurement where isolation is needed. Noise limits low current performance.

  * Hall effect
  * Isolated: 450V rms working voltage or higher, depending on standard.
  * ~100uR conductor
  * 3.0 - 5.5V supply
  * 120kHz
  * 10mV noise typical, with 10nF output filter. Corresponds to 0.25A.
  * +-35mV offset
  * 2% typ total error
  * Zero current output is half Vcc.

[[https://www.allegromicro.com/-/media/files/datasheets/acs758-datasheet.pdf]]

LCB-050B variant:
+-50A, 40mV/A typ. Ratiometric though - I think that is 40mV at 5V and changes with Vcc.

There are higher current variants.

==== Module ====

Purple Aliexpress module also has a TLC2272 opamp as a buffer after an RC filter. Sensor output is high impedance.

[[https://www.ti.com/lit/ds/symlink/tlc2272.pdf]]

  * Opamp supply: +-2.2 to +-8V
  * Input recommended max Vdd - 1.5. At 5V in, that is 3.5V.
  * ACS758 will put out 4.5V with that supply and 50A measured.

This looks like an unsuitable choice of amp for general use.

Module pinout:
  * Vcc: 3.3V or 5V ok. For 50A it wants to put out Vcc/2 + 2V, so will need at least 4V.
  * Out1: Output of RC filter.
  * Out 2: RC filter through buffer amp. Probably want to just use this one.