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Fluctuating ADC Reading for 4-20mA Pressure transducer input?

Discussion in 'Microcontrollers, Programming and IoT' started by MiguelHayden, Mar 5, 2020.

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  1. MiguelHayden


    Mar 5, 2020

    I am working on one project of water pressure measurement, in which i used pressure transducer which gives me output between 4-20mA Current form.

    I am using one 250 ohm resistance to convert current into voltage, and than i give this voltage to ADC of arduino UNO channel 0 (A0).

    ADC reading is continuously fluctuating up to 10 decimal numbers.

    I have also check by connecting multi-meter and measure sensor current reading, for particular pressure. but current reading is stable (even not fluctuate 1 or 2 points.)

    also i have checked voltage value after 250 Ohms +Ve and ground. converted voltage is also showing very stable.

    but why ADC reading is fluctuating..?

    i am using arduino uno, i doesn't have any changes in AREF, AVCC etc...

    please suggest effective solution,

    Thank in advance.
  2. Nanren888


    Nov 8, 2015
    Have you tried the ADC with a known constant input, such as a voltage derived from the power supply or other regulated source? Might confirm your ADC and use of it are good.
  3. Alec_t


    Jul 7, 2015
    Are you using screened cable between the transducer and the Arduino?
  4. Bluejets


    Oct 5, 2014
    You'll need to take an average reading over say 10 readings.
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    The measuring principles of a multimeter and of an ADC in a microcontroller differ considerably: A multimeter typically uses an integrating measurement method which will reduce noise and even suppress 50 Hz /60 Hz hum if designed correctly. A microcontroller's ADC on the contrary will make measurements of instantaneous values (with respect to the sampling rate). These tend to be more or less noisy. Averaging, as @Bluejets recommends, will reduce the noise. Also a small capacitor (e.g. 10 nF or 100 nF) across teh ADC input may help to suppress noise. So will the use of screened (shielded) cable as suggested by @Alec_t . Connect the screen (shield) to the ground of your system (arduino 0 V).

    You may want to read this article on filtering noisy arduino measurements.
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