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4-20 ma transmitter circuit design

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vik1501

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Can u help me design 4-20 ma transmitter which will convert voltage between 0-5V (I intend to use a DAC for this) to proportionate output current.
 
Let me get your answer:
You want to build a transmitter, that consumes between 4 and 20 mA
Then I don't get it. When you say transmitter, you mean a wireless data transmitter, or something else?

If you want to have a linear output current, depending on 0-5V input, just put a resistor in series (between the output of the system and the input of the next stage).
 
vik1501 said:
Can u help me design 4-20 ma transmitter which will convert voltage between 0-5V (I intend to use a DAC for this) to proportionate output current.

I don't understand your question either.

Len
 
to change 0-5 volt to 4-20ma loop current. most that i have seen use op-amps their are many plug in mods to do this with some have switch programable for input to output combinations and different powering as 12 vdc to 120 ac. So what are you trying to do?

joe
 
Ok !! Let me explain in details.

I am trying to build a flowmeter which converts the pulse train output of a transducer to digital code using microcontroller which is given to a DAC.

Please ref. to attached pdf file or download it ->

www.analog.com/UploadedFiles/ Application_Notes/266329066AN21.pdf


However I face following problem.

1. I want to use DAC which is unipolar rather than bipolar to achieve this.
2. The circuit should be able to convert this transducer reading to proportionate 4-20 ma current loop ( of course after calibration )

If u have any other queries plz let me know.
 

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  • analog_an21_4-20ma.pdf
    163.4 KB · Views: 1,817
4 to 20 mA Driver

What kind of accuracy is required ?
(if this is a car fuel monitor then the sensor may not be that good anyway --- +/-10% ???)

Does the output current have to use the zero volt rail as one of the output terminals ?
(if you are driving a moving coil meter then the output could be independent of 0v ?)

What supply voltage(s) can be used ?
 
1. Accuracy should be +/- 2%
2. Yes , one of the output terminal is 0 V rail.
3. Supply voltages 16-30V.


any other :?:

Supplementary :?: How do one connect such mutiple 4-20 ma devices to a single receiver.
 
let me suggest that if you are building one from scratch to use a pulsed out put device a (optical encoder) with quad out so you can count backwards. Take this pulse train direct into a processor from start x amount of pulses are one flow unit x amount of units is total amount, measured over a time frame 60 minutes, seconds gives you flow rate....you would have to write a program too....i have done this once with a embedded processor for a control system. It had a screen display that you could make it show info in numbers or graphics.
joe
 
Idea it to convert pulses received from a tranducer which is installed in flow to a calibrated 4-20 ma output. I am trying to measure flow between 40 to 100 litres per minute and send this information over 4-20 ma current loop to a controller.
 
Pink Panter
I guess you can use an IC that does the job you want.
Or check national semiconductor for a design they have in the site about 4 - 20 ma. transmitter, this is done by a diff opamp.

**broken link removed**

c u
 
the circuit in your posting will work if your transducer has 8 bit output if it is only a 0-5 square wave pluse train output it won't. what is the transducer make model ect ... maybe i don't understand what signal you are starting with.
joe
 
Check also Burr Brown

Burr Brown had lot of those albeit quite expensive. (The best. One of them suitable to be driven by a 0 to 5 V signal).

Just in case read the PDF. (The first article).

Elektor magazine brought one simple circuit in the Spanish version no too long ago. (The simplest I met).

Motorla sensors' manual had some examples.

National Semiconductors' op amps datasheet had at least one example.

Buena suerte.

Agustín Tomás
 

Attachments

  • loop_de_4_a_20_ma.pdf
    226.3 KB · Views: 1,063
go to DigiKey.com and spend $20 on AD693.
add voltage divider to scale 0-5V down to 0-30mV.
 
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