Hello,
I am wondering if a beaglebone black can be used to measure industrial 4-20 ma loops? I see there is an ADC feature, but the voltage range is only to 1.8V. Is it possible to set it up to work with the standard 24VDC circuitry involved with most 4-20ma loops?
Thank you in advance,
-JP
opamps are your friend
If you would think to Google “4-20 mA receiver” you could learn a lot.
Peripheral IC’s from TI and Maxim that have most everything you need all ready designed in.
Modules you could interface to the BBB, etc.
Application notes on how to design receivers, and things to worry about, common system problems that people have had with this circuit for the last 50 years.
Good luck.
There is a TI reference design for 4-20mA loop interfaces http://www.ti.com/tool/tida-00550. It is designed as a cape.
Iain
Hi
As I am also working on beaglebone to measure 4-20mA sensor output with Receiver module using less power
can anyone help me out with code to interface the 4-20mA current loop Receiver with beaglebone please ??
Hi, I’m designing ESD protections to 4-20 loop interface on Beagle Bone analogic input. which is the clamp voltage of any TVS zener that i could use? Thxs
cutting it a little close, so I recommend 68 ohm, which is a more
standard/easier to find value anyway. So, just terminate your 4-20mA line
with this resistor, and connect it to the Beaglebone analog input. Of
course if you're in an industrial environment you need to watch out for
transients, noise and interference, especially since the Beaglebone inputs
are famously fragile, so include some serious input protection (e.g. four
diodes connected as two anti-parallel 2-diode chains, with a filter cap
across it and maybe some series resistance). Then again, you could follow
evilwulfie's advice to use a dedicated buffer op-amp.
Use a 250 ohm (high precision, gold band) resistor, and install it inline with your 4-20mA, and it will give you 1-5V in place of 4-20mA. Your beaglebone can read voltage change. E.g. V=IR , V= 0.004Amps (4mA) Ă— 250 ohms = 1 volt.
Eg. 2. 12mA
Volts across 250ojm resistor at 12mA
V = 0.012Ă—250ohm
V=3 volt drop across a 250 home resistor with 12mA.
So programming is like this 1volt=4mA 2volt=8mA 3volt=12mA…
I hope this helps, if not look for videos of people doing this.
Joe,
Yes, but, as stated, the maximum voltage a BBBlack pin allows is 1.8v. Above 1.8 v, damage.
So . . . don’t use a 250 ohm resistor, if you’re using this method.
5v / 250 ohm = 0.02 amps (20 milliamps)
1.8v / 90 ohm = 0.02 amps ( 20 milliamps)