Or use current sinks of 1ma 2ma...... then the voltage does not have to be regulated ----- Original Message ----- From: "M. Adam Davis" To: Sent: Tuesday, July 08, 2003 6:18 PM Subject: Re: [EE]: 4-20 mA tutorial > As an example, I'm playing with a simple hall effect device now. This > one has VDD, GND, and an open collector output - which is simply shorted > to ground in a megnetice field (though there are others which will bias > the transistor based on the strangth of the field) > > Hook the VDD to the positive side of the current loop, the GND to > negative, and the output to the positive via a resister. The device > naturally consumes about 4mA. When in a magnetic field it'll short the > resister to ground and pull more current. > > You could also use many of these on one current loop in a binary > fashion, one pulls 1mA, another 2, 4, and 8. Use low power devices that > only consume 1mA each generally, and you can tell which switches are > closed. This method would require a regulated voltage on the loop. > > Typically the device reading the loop provides the voltage. I don't > know whether a typical loop expects a regulated voltage or not. > > -Adam > > Wouter van Ooijen wrote: > > >I am looking for an introduction/tutorial into 4-20mA 'transmission'. I > >am no fool, but have no idea about which party provides the power, > >whether it is to ground or from a positive voltage etc. > > > >Wouter van Ooijen > > > >-- ------------------------------------------- > >Van Ooijen Technische Informatica: www.voti.nl > >consultancy, development, PICmicro products > > > >-- > >http://www.piclist.com#nomail Going offline? Don't AutoReply us! > >email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > > > > > > > > > > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.