ADS1115 4mA Value Not Near 6430

Hardware
1

I’m using the ADS1115 Mini Module (https://store.ncd.io/product/1-channel-4-20-ma-current-loop-receiver-16-bit-ads1115-i2c-mini-module/) to connect to an Ashcroft G2 Pressure Transducer (4-20mA) (Pressure | Pressure Sensor| G2 Pressure Transducer | Ashcroft).

When I connect this sensor to a PSU and measure 0 psi with my DMM, I get 4mA flat as expected.
I have the ADS1115 module powered by USB, CIN connected to the G2 V+, G2 V- connected to ADS 1115 Ground. At 0 psi I was getting a Digital Value of Analog Input at Channel 1 closer to 5900 (hopped around a little bit, but not far off).

I’m using the SingleSided.ino from GitHub - ncdcommunity/Arduino_Library_ADS1115_16Bit_4Channel_ADC: ADS1115 16bit 4Channel Analog Digital Converter Interface With Arduino
I changed my rate to 8SPS to steady out the readings a bit.

Using the original 0.000622 scale factor gave me converted pressure readings that disagreed with the other (non-calibrated) sensors in my test setup. When I adjusted the scale factor to 4mA/5900 = 0.000678, my converted pressure values agreed with my other pressure sensors.

In short, my 4mA raw value is less than expected, but when I ‘recalibrate’ to the 4mA raw value I do have, everything seems to work. Is there a reason my 4mA value is so far off the expected 6430?

2

the part used on the convert mA to voltage has a 3% tolerance.

3

Hello Bhaskar,

Since my part at 4mA is much over 3% away from the expected value, should I assume my part is out of tolerance and faulty?

EDIT: I’ve changed my setup to have my DMM inline with the DS1115 module and it looks like all the conversions are right-on between the two. So I’m not sure what to attribute my different starting value and thus different conversion factor to, but everything is working great with that change.