Reply To: Precise analog voltage measurement using Arduino

Thanks for the reply @neilh. The meters are commercial grade (read that as $$$$$), and USU will eventually work them into their building automation (SCADA) system. But, they don’t have it deployed yet in all the buildings and so I need a cheap way to collect high frequency data from the meters and get them on USU’s network until that happens – hence my attempt with the Arduino Ethernet.

The meters are ultrasonic and have an actuation flow of 1/16 gal/min. So, anything less than that should be output as 4 mA on the 4-20 mA output from the meter. Obviously, there are limits to the accuracy of the meters themselves at flows that low. The top end of the meter output is configurable (e.g., I can set the max flow rate that is output from the meter as 20 mA).

So, theoretically, if I choose to integrate a stable voltage reference of 4.096 V via a breakout (I ordered one today), I set the top end of the meter output at 50 gal/min (which is probably reasonable for these buildings), and calculate the theoretical resolution I should get with the 10-bit ADC on the UNO, I get 1/16 gal/min. This might be OK for my needs. I’m going to test tomorrow on a meter that they just installed this week, so I’ll have some real data to have a look at.

As an aside – I would love to use the Mayfly. I’ve got one, and I’m working with Stroud on a project right now that will be using them. I really like the specs. Two things pushed me toward the UNO:

1. The ability to input 12 V on the barrel power jack and supply 12 V to power my 4-20 mA current loop using the Vin pin
2. I think I need Ethernet to reliably get them on USU’s network because WIFI is a little iffy in some of the spaces where these meters are located (although, I did get an XBee WIFI module working nicely with the Mayfly).