I still use analog 4-20 mA current loops in new designs. They are=20 reliable and robust. I also implemented my own version back in the '90s for our oven=20 control system panels: 1-5 mA instead of 4-20 mA. Each catalytic=20 heater in the industrial process oven has a thermocouple embedded in=20 the catalyst pad. Most of the ovens that we built controls for have=20 anywhere from 12 to more than 100 individual heaters. The=20 thermocouple 2-wire transmitters that I designed needed significantly=20 less than 1mA to operate. It just made sense to scale everything=20 down by a factor of 4 so as to reduce the power supply size required=20 to run all those thermocouple transmitters as well as reduce the heat=20 buildup inside the cabinets (from the burden resistors on the CPU cards). dwayne At 11:59 AM 12/3/2014, John Ferrell wrote: >You are correct. As I recall the Teletype machine would sit there doing >idle cycles on an open line. >But I still like the 4-20ma standard! > >On 12/3/2014 1:41 PM, Dwayne Reid wrote: > > Hi there. > > > > I'm pretty sure the above is not correct, at least for Canada. I'm > > positive that a mark was 0 ma (open) and space was 20 mA > > (ish). Might you be confusing this with industrial 4-20 mA current > > loops for analog data transmission? > > > > dwayne > >-- >John Ferrell W8CCW > Julian NC 27283 > It is better to walk alone, >than with a crowd going the wrong direction. > --Diane Grant --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .