RFL Communications 21 Sub-MUX Especificaciones descargar pdf (Pagina 215)

December 2008 Page 17–3

Chapter 17. Pilot Wire Interface (HCB/SPD) Module

17

Figure 17–3. HCB/HCB-1 Interface Module

for Three-Terminal Applications.

Figures 17-3 and 17-4 show the rear interface

modules for three-terminal line applications.

These modules are double width because, for a

three-terminal line application, you must attach

one three-terminal interface to two adjacent HCB

modules. This double-width rear interface module

properly connects the two HCB modules together.

As with the two-terminal interface modules, the

SPD version has a 4/1 matching transformer

(enclosed in a bright metal can) mounted on it,

while the HCB/HCB-1 version does not.

Figure 17–4. SPD Interface Module

for Three-Terminal Applications.

Another important difference between

HCB/HCB-1 and SPD applications is in the

connection itself. When you connect the module

to an existing

HCB/HCB-1 application, you will

see a ground on one of the pilot wire leads

somewhere between the relay and the old insu-

lating transformer. This ground must be removed.

The appropriate ground connection is made inside

the interface module attached to the rear of the

FOCUS chassis.

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