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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>
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