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

[MiguelHayden]

Hello...

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.

 

[Nanren888]

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.

 

[Alec_t]

Are you using screened cable between the transducer and the Arduino?

 

[Bluejets]

You'll need to take an average reading over say 10 readings.

 

[Harald Kapp]

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.

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.