Specifications

Section 4: Wiring
4-13
4.6 SE 744-A MSM INTERFACE
WIRING
Each SE 774-A MSM can be used to interface up to four monitor point contacts and one reader
with each reader port on the Alto 818.
4.6.1 READER CONNECTIONS
The SE 774-A MSM is a series connection between a reader and an Alto 818 reader port. The
MSM has two female coax connectors for this purpose and it makes no difference which one
is used to connect to the reader and which one to the ACU. The MSM counts as one splice in
a reader-to-ACU coax cable run. As such, it can be located at any point between the reader and
the ACU. The maximum length for this cable run depends upon the reader model (see
specifications for the reader).
4.6.2 MONITOR POINT CONNECTIONS
The MSM has four monitor point contact pairs. Monitor points are connected to the MSM with
unshielded, twisted pair wires, size AWG 22 or larger. The contact-to-MSM distance can be no
more than 200 feet (61m).
The monitor point contacts twisted pair wires connect to a terminal block mounted on the face
of the MSM. As shown in Figure 4-10, the method of connection depends upon whether the
monitoring contacts are normally open (N/O) contacts or are normally closed (N/C) contacts.
For N/O monitoring contacts, a 36K-ohm resistor must be connected in parallel with the
contacts; for N/C monitoring contacts, a 36K-ohm resistor must be connected in series with the
contacts.
CAUTION:
A 36K-ohm resistor must be installed across all MSM contact pairs, used or not.