GAI-Tronics 12578-002 Monitored Input Module (MIM) - Manual (Page 7)

Pub. 42004-711L2B
Model 12578-002 Monitored Input Module (MIM) Page 7 of 12
f:\standard ioms - current release\42004 instr. manuals\42004-711l2b.doc
01/09
Mode 3: IDC Single Normally-Closed (N.C.) Switch
In this configuration, only one normally-closed dry contact closure may be installed per supervised line.
In this mode, the loop is monitored for open circuits, wire-to-wire short circuits (across + and -), and
ground faults. When the contact closure is not active (closed), the 15 k
Ω is bypassed and the circuit sees
only the 5.1 k
Ω load.
Figure 4. IDC Single Normally-Closed Switch
When the contact closure is active (open), the loop appears as a 20.1 k
Ω load (15 kΩ in series with 5.1
k
Ω). This changes the value of the input and indicates to the MIM that the contact closure is active. If
there is a short across + and -, if either leg is grounded, or if a break occurs on either leg, the MIM
indicates that a fault has occurred.
N OTE : The terminating resistors are not included with the MIM. These resistors are included in a kit
(12509-003) that must be ordered separately.
Mode 4: IAC Line Supervision
(Reserved for 12579-002 Monitored Relay Module)