On 4/10/22 12:23, Martin Bishop wrote: > Chuck > > My error, you said 20 mA current loop, I bowdlerised it as parallel port. I > have a punch with a parallel interface ... I can't recollect ever using a > current loop interface on equipment, although I have met many in old > documents. 4 .. 20 mA current loops reporting e.g. pressure actuated > potentiometers are however old friends, if that is the correct term. As you > observe current loop has good noise immunity.
There is a tie-in to parallel port, although somewhat tangentially. Back in the 80s and 90s, CL was promoted as a long-haul solution to (as well as other things) distant printers. In particular, I remember Inmac flogging them. --Chuck