GAI-Tronics 12578-002 Monitored Input Module (MIM) - Manual (Page 6)

Pub. 42004-711L2B
Model 12578-002 Monitored Input Module (MIM) Page 6 of 12
f:\standard ioms - current release\42004 instr. manuals\42004-711l2b.doc
01/09
Model 2: IDC Single Normally-Open (N.O.) Switch
In this configuration, only one normally-open 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 (open), the loop appears as 20.1 k
Ω load (15 kΩ in series
with 5.1 k
Ω). This appears on the input to the MIM and indicates a healthy loop. When the contact
closure is active (closed), the 15 k
Ω resistor is bypassed.
Figure 3. IDC Single Normally-Open Switch
The circuit then sees only the 5.1 k
Ω load. 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.