4-20mA sensor integration

Community Playground General Discussions
1

Curious what can be done to get readings from 4-20 mA sensor loops? Thinking using an Arduino for the input and then interfacing it with the Vera.

Tried searching the forum but nothing relevant came up for “4-20” keywords.

Links appreciated - Thanks!

2

Fascinating; I’d never heard of this technology. I think you’re the first to try interfacing it with MiOS. Definitely an Arduino would work, measuring the analogue voltage across a known resistance.

3

Not that it will help, but you might be better using 1 wire, you can either use an arduino and create a plugin to interface with vera or use the embedded systems 1 wire setup and use Chris’s plugin to interface to vera.

  • Garrett
4

In industrial/HVAC automation (my old field), analog sensors are generally designed to deliver a 4-20mA current output, with 4mA as the low and 20mA as a high.

Over the years we relied on the commonality to do anything that was slightly outside the norm, or to make practically any sensor available work as long as it wasn’t limited to a tight range.

One project involving automated windows had a spec that only allowed the window motors to be enabled under a certain wind speed and provided the wind wasn’t hitting at an angle that could damage/wear out the armatures.

So we bought an anemometer/wind vane combo built for sailboats, attached it to the roof of the building, wired both for 4-20mA, and then used the readings to assign speeds and directions we based the logic on.

Here’s a Primer

5

[quote=“garrettwp, post:3, topic:170181”]Not that it will help, but you might be better using 1 wire, you can either use an arduino and create a plugin to interface with vera or use the embedded systems 1 wire setup and use Chris’s plugin to interface to vera.

  • Garrett[/quote]

Hmm… interesting…have never heard of 1-wire before this.

6

They are fairly cheap and you can wire them up onto one digital pin of the arduino. There are some libraries out there that make using them with the arduino pretty easy. I just bought some arduino parts and xbee modules to create a wire 1-wire setup using the temperature sensors to mount in my rooms of my 2nd floor.

Some links:

http://www.arduino.cc/playground/Learning/OneWire

  • Garrett
7

I just created a plugin using the Arduino. I recommend the Nano due to it having an FTDI chip on it which works perfectly with the Vera USB driver. The Nano is supposed to be able to handle currents in excess of 20ma, but I am using 1ma in my application, so I don’t have any practical knowledge of it’s tolerances.

8

I picked up an Arduino Uno, Mega 2560 and also a teensy. I am curious to know if the teensy will work well with Vera if hooked up via usb, as it has a usb chip, leaving the serial interface free for other uses e.g. xbee module and so forth. My plans are to have the arduino hooked up via the network and the sensors communicate via xbee.

  • Garrett