Post by thread:burr-brown rcv420

hello all, i rec'd this reply when i tried to purchase a rcv420: >on your reqest for the burr brown rcv420 you would have to buy 17 >pieces at 4. 68 each. we have stock. also for your information this part >has been discontinu ed as of 7-25-97. when our stock is gone we will not >be able to replace it. >thank you. does anyone know of a similar chip? this chip converts the 4 - 20 ma loop directly to 0 - 5 volts to be read on a dvm or pic with an a/d. i only need to connect a couple of devices. i really don't want to purchase 17 pieces and also i don't want to purchase 17 pieces that will be discontinued. i suppose i could use a similar circuit. i realize the rcv420 voltage cannot be ground referenced. i don't work with 4 - 20 ma loops very often. roger

Use a good quality resistor of around 220R 0.88V - 4.4V span for 4-20mA Tony PicNPoke Multimedia 16F84 Beginners PIC Tools. **PLUS** - PicNPlay - PicNPlan - PicNPrep - PicNPost PicNPort - DT Type Saver - *new* PicNQuiz. Recent addition - Hex To Source converter. http://www.picnpoke.com Email spam_OUTpicnpokeTakeThisOuTcdi.com.au

>does anyone know of a similar chip? this chip converts the 4 - 20 ma >loop directly to 0 - 5 volts to be read on a dvm or pic with an a/d. i >only need to connect a couple of devices. i really don't want to >purchase 17 pieces and also i don't want to purchase 17 pieces that will >be discontinued. > >i suppose i could use a similar circuit. i realize the rcv420 voltage >cannot be ground referenced. You can use a 250 Ohm resistor directly - you will end up with a voltage from 1 to 5 Vdc. You feed that into your A/D. Two things to watch out for: use an accurate resistor (0.1% accurate is about a buck) and make sure that you don't introduce any unplanned current paths. In other words, if you have no control over where the 4-20 mA is coming from, make sure that YOUR circuit is floating and not referenced to anything else. If you have to reference your circuit to something else, use an isolation amplifier between the resistor and your A/D (or use a serial A/D, power it seperately, and use opto isolators to get the control and data to and from the A/D). Note that you have a 1 V offset (the minimum current of 4 mA through 250 Ohms = 1 Volt). Just account for it in software. dwayne Dwayne Reid <.....dwaynerKILLspam@spam@planet.eon.net> Trinity Electronics Systems Ltd Edmonton, AB, CANADA (403) 489-3199 voice (403) 487-6397 fax

TONY NIXON 54964 wrote: > Use a good quality resistor of around 220R > > 0.88V - 4.4V span for 4-20mA You get high quality 250ohm resistors made for this purposeto give you 1V - 5V. -- Friendly Regards Tjaart van der Walt tjaartKILLspamwasp.co.za Add your voice !! Vote at the Great G Com Public Vote. Go to : http://www.wasp.co.za/~tjaart/gcomvote.html |--------------------------------------------------| | WASP International | |R&D Engineer : GSM peripheral services development| |--------------------------------------------------| |SMS .....0832123443KILLspam.....wasp.co.za (160 chars max)| | http://www.wasp.co.za/~tjaart/index.html | |Voice: +27-(0)11-622-8686 Fax: +27-(0)11-622-8973| | WGS-84 : 26¡10.52'S 28¡06.19'E | |--------------------------------------------------|