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  <http://www.ptialaska.net/~floyd>