E+M signaling (Floyd Davidson)Index Home About From: floyd@tanana.polarnet.com (Floyd Davidson) Newsgroups: alt.engineering.electrical,comp.dcom.telecom.tech Subject: Simplified E&M signaling types (was Re: E&M Type V) Date: 19 Jan 1999 08:56:33 GMT >> I think Type I has M going to battery >> continuously for a request and E going to ground continuously for >> a response. I don't remember the other types... > >I'd have to look it up, but I'm pretty sure that the "types" have to >do with whether theE and M leads are active when pulled to battery >or when pulled to ground. Type I E&M (the original and most commonly seen E&M signaling design in the US) uses the M lead to signal from the trunk circuit to the signaling unit, and the E lead for the opposite direction. Both directions employ a single lead, utilizing a common ground for return. The M lead from the trunk sends a battery/ground signal which operates a simple relay that has a ground return. The E lead sends an open/ground signal and operates a simple relay that has a battery return. It is a 2-wire arrangment using a single pair. P relay M relay coil contacts +-+ -48 -------X--+---o >--- M lead ---> o-------| |------GND | +-+ --- | Gnd E relay coil R relay contacts +-+ -48 -------| |----o <--- E lead <--- o--------X------GND +-+ TRUNK CIRCUIT SIGNALING UNIT Type II E&M functions simularly, except it is a 4-wire arrangment using one pair in each direction. The M lead is matched with an SB lead, that provides the -48 volts from the signaling unit side to the trunk circuit side (and the M lead is battery/open instead of battery/ground). The E lead is matched with an SG lead that provides ground from the Trunk Circuit side to the singaling unit. The M relay is replaced with a transistor voltage detection circuit, and the E relay is replaced with a Ferrod Sensor device which allows significantly lower current to flow in the E lead. The purpose is to eliminate the use of a common ground return. The signaling unit provides both battery and ground for the M lead, and the trunk circuit provides both battery and ground for the E lead. Type II E&M is rarely used. (See drawing for Type IV E&M. Imagine the M relay is replaced with a transistor circuit...) Type III E&M is also a 4-wire circuit. The SB and SG leads also provide battery and ground respectively, but only for the M lead. Both originate with the signaling unit. The E lead is as for Type I E&M, except Type III E&M uses transistor and Ferrod circuits similar to Type II. Type III E&M is rarely used. (See drawing for Type IV E&M. Use more imagination than I'm willing to either draw or describe for something that is never used. Note that the Type III M lead provides battery/ground similar to Type I, while Type II, IV and V M leads all provide battery/open.) Type IV E&M is arranged exactly like Type II E&M, except that a mechanical relay is used for the M relay as in Type I E&M. P relay M relay coil contacts +-+ +------X--+---o >--- M lead ---> o-------| |------ GND | +-+ +-------------o <--- SB lead <--- o---------------- -48 Ferrod Sensor E relay circuit contacts +-+ -48 -------| |----o <--- E lead <--- o--------X------+ +-+ | GND --------------o >--- SG lead >--- o---------------+ TRUNK CIRCUIT SIGNALING UNIT Type V E&M is a symetical *unbalanced* variation that is used virtually everywhere except in the US. P relay M relay coil contacts +-+ GND --------X-----o >--- M lead >--- o-------| |----- -48 +-+ E relay coil R relay contacts +-+ -48 -------| |----o <--- E lead <--- o--------X------GND +-+ TRUNK CIRCUIT SIGNALING UNIT Floyd -- Floyd L. Davidson floyd@ptialaska.net Ukpeagvik (Barrow, Alaska) floyd@barrow.com Pictures of the North Slope at Search for Google's copy of this article Index Home About