I am measuring the current of the ignition coil using the hall effect sensor(ACS712)Datasheet. But the output of the hall effect sensor is pulsed analog signal. At zero current the output voltage is 2.5 volt. During operation the output is from 2.5 to 4.5 based on the current reading.

Now i need to measure the peak of the pulsed analog signal using Ni DAQ. Now what should i do.

  1. Smoothing the signal using RC filter is good way or using software filter is good wayenter image description here

Igniter coil is operated at 192 Hz at 25% duty cycle frequency is generated using 555 IC

Igniter coil is operated at 192 Hz at 25% duty cycle. Frequency is generated using 555 IC

  • \$\begingroup\$ what current sensors? there is no information provided. Does this HallEffectSensor output a mark space ratio associated with the current or is this pulse due to something else. Step back and think... is there enough information present for people who have zero idea what you are doing \$\endgroup\$
    – user16222
    Oct 20, 2018 at 11:07
  • \$\begingroup\$ @JonRB acs712 current sensor the output of sensor is analog voltage proportional to the current (increase in voltage when positive current flow is increased ) \$\endgroup\$
    Oct 20, 2018 at 11:17
  • \$\begingroup\$ @HEMARAJJ: Add in a link to the datasheet. Make it easy for those you are asking to help. \$\endgroup\$
    – Transistor
    Oct 20, 2018 at 11:20
  • \$\begingroup\$ You've already measured it, on your oscilloscope. What's the problem with that measurement? Shoving a pulse signal through a filter is a good way to destroy any accuracy around the peak, so there's no way for us to guess what you're really trying to achieve. \$\endgroup\$
    – Neil_UK
    Oct 20, 2018 at 11:36
  • \$\begingroup\$ @Neil_UK I am trying to measure the value in DAQ. the output of the ACS712 is in 245 Hz and Daq is reading the the sensor at range of 100 samples at 1khz. So i am not able to measure the value correctly. \$\endgroup\$
    Oct 20, 2018 at 11:51

2 Answers 2


As the waveform has sub-ms features, you need to sample with a much smaller period, say 10kHz, to see detail around the peak.

If you are stuck with only sampling at 100Hz, you would need to lowpass filter to less than 50Hz, which would destroy all the detail of the pulses, in particular the peak heights. However, you could make some measurements with your oscilloscope that could allow you to relate the proper measurement you have already made to a measurement through a lowpass filter, making some assumptions that the pulse shape and frequency stays the same.

Does the DAQ have a lowpass filter on its input, or does it sample? If it samples, then you can get stochastic information from simply taking a lot of samples, as long as the sampling is uncorrelated with the signal pulses. You will lose the shape of the waveform, but you will learn what voltage value the waveform exceeds for 90% of its time, or 99% of its time, which might be a good proxy for the peak.


you're just measuring peaks? Look into a peak detect circuit. Or a sample-and-hold triggered by the falling edge (?) with a faster filter. Maybe the NI can do this.


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