Creating 4 to 20MA ?

[amgen]

do anyone have knowledge of how to do circuitry for outputting the industry standard of 4-20ma, a internet search for "circuitry of/for 4 to 20MA" was fruitless.
Some devices give the MA output from internal means or external DC supply thus governing the current.

thanks,
don
amgen

PS; did I not call the thermal switch in dc motor early on ??!!

[mackrackit]

Are you wanting to make a sensor that outputs the signal or wanting to know how to read the signal?

If it is reading the signal you want this may help
http://www.omega.com/techref/das/4-20ma.html

If you are making you own sensor, what type and method are you planning?

Here is an article about current sources.
http://en.wikipedia.org/wiki/Current_source

And some other stuff.
http://www.sensorland.com/HowPage028.html
http://en.wikipedia.org/wiki/Current_loop

[Archangel]

PS; did I not call the thermal switch in dc motor early on ??!!
Yes you did, And a good call it was too !

[mackrackit]

PS; did I not call the thermal switch in dc motor early on ??!!
How did you know with the info given?

[Archangel]

How did you know with the info given?
Probably borrowed mister_e's crystal ball, speakin' of Mister_e, where the heck is he ?

[Ioannis]

Steve is a magnet for accidents. Hope he is doing much better now after testing how strong a car is...

Ioannis

[Luciano]

Hi,

4-20mA Current Loop Primer:
http://www.murata-ps.com/data/meters/dms-an20.pdf

Best regards,

Luciano

[mat janssen]

Here a schematic diagram I always use when using pic pwm and analog out.

[amgen]

thankyou for links which I read all.

Would like to make PIC ckts to output the 4-20 MA stuff.

what I know (maybe), recieve ma. is easy, just read V across a 100 to 250 ohm resister and scale/calculate or limit the a/d reading. PIC can do 10 bit but many products reach to 12 or 14 bits.
Send or creating ma signal seems a little more involved, apparently needed is 12 to 24 vdc supply to be able to adjust for wire and other loop resistance ??
Getting a good DC level (0 to 5) volts from PIC with 1000 or more resolution --- not so easy. See diagram, and how to set limits of 4 and 20 ma with resisters ???
.
.
.
motor t-stat
used simple process of elimination (mental process that is) the 2-A and F wires are generally all thats needed to run motor in both directions and more times than not, two small wires will be for temp sw.

don

[Luciano]

Hi,

See this link:
http://www.maxim-ic.com/appnotes.cfm/appnote_number/722/

Best regards,

Luciano

[martintorres]

7334

Hello, last night very nearly completely finished my hardware to read 4-20mA (24VDC) and generate a PWM 4-20mA (24VDC) ... Everything runs based on two LM358 with single source (one is supplied 12Vdc and the other to 24VDC). GND is shared between the two operational amplifiers.
I share the diagram, if you need anything else, ask me and I will share it...
To read the 4-20mA signal and place it on the display, as I was tired last night and I can not think of anything to work with floating point, implement the following lines:



ADCIN 0, ent420
nivel = ent420
aux1=(ent420*100)/250 ;(V*100)/(R*100)
aux1= aux1 *2
;****blabla bla
LCDOUT $FE, 1
LCDOut $fe,2,"Sal: ",DEC4 aux1,"mA"


to generate the pwm to take me filter 0-5Vdc to create the 4-20mA, implement these lines:



PWM PORTC.2,nivelAUX,100 ;nivel PWM = (Vout * 255) / V.Fuente


Sorry for my spanglish!!!! :D

En Español
Hola, anoche termine casi casi por completo mi hardware para poder leer señales 4-20mA (24Vcc) y generar con un PWM 4-20mA (24Vcc)... Todo corre en base a dos LM358 con fuente simple (uno se alimenta a 12Vcc y el otro a 24Vcc). GND se comparte entre ambos amplificadores operacionales.
Te comparto el diagrama, si necesitas algo mas, me pedis y te lo comparto
Para leer la señal 4-20mA y colocarlo en el display, como anoche estaba cansado y no se me ocurria nada para trabajar con punto flotante, implemente las siguientes lineas:



ADCIN 0, ent420
nivel = ent420
aux1=(ent420*100)/250 ;(V*100)/(R*100)
aux1= aux1 *2
;****blabla bla
LCDOUT $FE, 1
LCDOut $fe,2,"Sal: ",DEC4 aux1,"mA"


para generar el pwm que me lleve el filtro de 0-5Vcc para crear los 4-20mA, implemente estas lineas:



PWM PORTC.2,nivelAUX,100 ;nivel PWM = (Vout * 255) / V.Fuente