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I am trying to measure current from Ignition coil(12V, 4.5A). i used arduino to measure current. And it worked good. And i connected the ACS712 signal pin to NI DAQ 9215. At zero current the output voltage is 2.5v( ACS offset votlage ) which is showing correct in LABVIEW 2017 . But there is no change in voltage when the ignition coil is turned on.

This is thing i got when i measured the signal from current sensor using oscilloscope.

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I found the problem for my question. i placed acs-712 to lower side of MOSFET and measured the signal in oscilloscope. and i got the output signal in LABVIEW also.

But the signal is sill noisy in LABVIEW oscillates between 2.5 to 4. I think i should filter the signal.

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JRE
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HEMARAJ J
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  • You have your load and source pins swapped but that shouldn't be a problem since if this has an offset voltage it should be bidirectional. Is the 4.5A continuous, or just a pulse? – Hearth Oct 18 '18 at 14:29
  • Spark plug is running at 192 Hz with 20% duty cycle. So it's definitely a pulsed current. – HEMARAJ J Oct 18 '18 at 14:36
  • @HEMARAJJ - (a) The ACS712 pin numbering shown on your schematic doesn't match its datasheet. I suspect perhaps you are using some kind of pre-made ACS712 *module*, not a bare ACS712, and that is misleading the readers. Please give more details about your *real* hardware. (b) What happens when you view the ACS712 output signal with an oscilloscope instead of the DAQ? (c) Are you saying that you used *exactly* the same circuit and components, with the ACS712 output connected to an Arduino analog input, and saw the expected varying signal? Or did you make other changes after your Arduino test? – SamGibson Oct 18 '18 at 15:54
  • @SamGibson This is hardware i am using (https://components101.com/sensors/acs712-current-sensor-module). Not viewed the signal in oscilloscope, Made some changes in the above circuit i powered the ACS712 from my arduino. I am facing some problem if connect the acs712 to above circuit ( Connected using 7805 ) – HEMARAJ J Oct 18 '18 at 18:05
  • @HEMARAJJ - (a) Thanks, so my guess was right and the schematic is incomplete as it doesn't explain that is is an ACS712 *module*, which has extra components on it. Also, the PCB layout on that [website](https://components101.com/sensors/acs712-current-sensor-module) doesn't even match their own photos, so can we trust the accuracy of anything they say? (b) So please view that signal with an oscilloscope and update the question with the result (e.g. scope trace screenshots etc.). (c) I didn't understand the next part of your reply. I can't help further unless your replies are *clear* :-( – SamGibson Oct 18 '18 at 19:17
  • @SamGibson i measured the signal from ACS 712 in oscilloscope. I updated the the image above. And output signal is pulsed signal. – HEMARAJ J Oct 19 '18 at 10:27
  • @HEMARAJJ - Thanks for the scope trace, but IMHO it makes no sense. Two things immediately "stand out": (a) The whole signal is negative, compared to the scopes reference (i.e. the probe's earth). For channel 1, the 0V reference point is shown by the `1` on the left side - and the whole signal is below that. But you said the signal idled at 2.5V! (b) The scope says the signal is 36V p-p. Ignoring the spikes of noise, it looks more like approx 20V p-p to me. Even so, that is impossible for the ACS712 output (the IC only has a 5V unipolar supply). You should investigate that invalid trace IMHO. – SamGibson Oct 20 '18 at 02:42
  • @SamGibson Thank you for the comment, i made some updates. – HEMARAJ J Oct 20 '18 at 07:16

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