4-20ma current source

[Beepboop]

How does the process meter in Dave's video generate the 4-20ma current? As it does not seem to have an voltage to current chip or a dac that outputs current. https://youtu.be/y3h02BDPMJw

[ebastler]

A current source can be as simple as this:


https://en.wikipedia.org/wiki/Current_source

No idea what circuit that meter uses, though.

[timmy88]

I can't open your youtube link for some reason

[ogden]

I can't open your youtube link for some reason

It's EEVblog #1248

[Beepboop]

Im more looking for an answer to how it adjusts the current and does it precisely.

[ogden]

https://en.wikipedia.org/wiki/Current_mirror

https://www.analog.com/en/design-center/reference-designs/circuit-collections/precision-current-source.html

[Zero999]

Also check out the thread linked below:
https://www.eevblog.com/forum/projects/4-20ma-current-loop-185196/msg2398887/#msg2398887

If you don't have time to read the thread. Here's a circuit posted from it. V1 is the 24V supply voltage, powering the loop, which will draw 4mA to 20mA, as V2, the input voltage, is changed between 0V and 5V. V3 is a voltage reference, which can also power the circuit. This will work, as long as the current drawn by U1 and the device in question is under 4mA. Note the different ground symbols used to differentiate between the two 0V reference points.

[Beepboop]

Is the 24v supply a standard in these current loops? And how would the two  0V reference points be implemented?

[Vovk_Z]

Is the 24v supply a standard in these current loops?

- kind of. It gives a possibility to work with up to about 1000 Ohm load.

And how would the two  0V reference points be implemented?

- just don't connect them together.

[Zero999]

Is the 24v supply a standard in these current loops? And how would the two  0V reference points be implemented?

Yes, 24V is a fairly standard power supply.

0V is just a reference point, as mentioned above, in this case they should not be connected together.

Here's an application of the circuit, taken from the other thread. The 4mA to 20mA circuit is connected to a proximity sensor which outputs between 0V to 5V and the op-amp converts it to 4mA to 20mA. One 0V is used for sensing the current at the start of the cable, connected to the sensor and the other 0V is inside the sensor.

https://www.eevblog.com/forum/projects/4-20ma-current-loop-185196/msg2398887/#msg2398887