4-20 mA current loop regulation

This video demonstrates how the current output by a 2-wire transmitter is a function of the process measurement and not electrical parameters such as supply voltage or loop resistance.

Category:

Education

Tags:

• instrumentation
• current
• loop
• 4-20
• mA
• transmitter
• loop-powered
• 2-wire

[sfacp]

Great video! I am not new to electronics but it is my first time to work with 4-20mA current loop transducers and don't know much about the industry instrumentation standards.

Your video helps a lot! Now my question is, may I assume that all transducers with 4-20mA current output have constant current source built-in?

[BTCInstrumentation]

@sfacp If the sensor is 4-20 mA DC, then you may safely assume it's got either a current regulator in it (2-wire) or a true current source in it (4-wire). Read the chapter in my book on analog instrumentation signals:

openbookproject (dot) net (slash) books (slash) socratic (slash) sinst (slash) book (slash) liii.pdf

[Mart34]

Excellant video. Whats the maximum loop resistance and less importantly, whats the max voltage you can apply ? cheers, mart

[BTCInstrumentation]

@Mart34 Most loop-powered transmitters have minimum and maximum terminal voltages ranging around 12 to 40 VDC. Specifications vary, so be sure to check the manufacturer documentation (datasheets, user's manuals) to get a definitive answer for your transmitter.

Maximum loop resistance is a function of minimum terminal voltage. Loop resistance drops voltage, taking away from the power supply voltage, leaving the transmitter whatever remains. R_max = (V_supply - V_min) / 20 mA

[nugent5438]

Hello, I am working on developing a simple training curriculum regarding 4-20ma current loops. I work in the industrial burner/boiler industry. Our industry has just about completely converted to 100% electronic controls and the use of 4-20ma current loops is very wide-spread. I am trying to find a nice simple, easy to view graphic of a 2-wire current loop circuit to demonstrate with. Would you happen to know a good example of one on the net or perhaps have one yourself? Any help would be great

[BTCInstrumentation]

@nugent5438 Sure thing: check out my free textbook online, with a whole chapter on analog instrumentation signals. Pardon the weird URL, as YouTUbe does not allow me to post it verbatim:

openbookproject (dot) net (slash) books (slash) socratic (slash) sinst (slash) book (slash) liii.pdf

[neil230163]

Hi, I plan to connect my a/d chip to a 4-20 ma sensor (a Honewell sensepoint). As my a/d is 0-5v input, I assume I would also connect the 0v from the power supply to my 0v on my board, as it has its own power supply. Would this be correct?

Thanks

Scott

[jacknay112]

Thanks for your upload and book.

[jaumetebe]

Molt ben explicat

[rpaul247]

Great stuff, your videos are the best on here.. thanks alot.

[sfacp]

@BTCInstrumentation Thanks a lot for your answer. And thank you for your book too. It 's a wonderful book for me to learn industry instrumentation. Do you offer a online course for this?