Honeywell Stereo System P520 Manual De Usuario

66-2066—01

6

A source impedance resistor is required when using the P520 

signal processor with S55X, S55XB and S55XBE series 

viewing heads. This resistor should be 330 ohms (factory 

installed) for viewing head cable runs up to 500 feet  (152 

meters), and it should be 150 ohms for cable runs of 500 feet 

to 1000 feet (152 to 305 meters). The resistor should be 

installed across the SC and SIG GND terminals. A 1/4 watt 

resistor is suitable.

It should be noted that the flame signal wire is shielded, and 

that the shield is terminated at both ends. The shield must be 

a braided type for this application in order to maintain an 

electrical path. For this reason, a foil type shield should not be 

used. This signal ground shield is also the self-checking or 

shutter drive circuit return path. It is recommended that 

Honeywell C328 or C330 cable be used for all applications 

(viewing head model dependent).

For detailed instructions on cable preparation and wiring the 

viewing head connector, refer to the applicable manual for the 

viewing head being installed.

Careful consideration should be given to the power supply 

used for the P520. 24VDC is used to back bias the “steering” 

rectifier, as shown in Fig. 3, to prevent the power from feeding 

into the 24VDC supply. Each P520 signal processor draws 

approximately 150mA, and each viewing head draws about 

100mA of current (24VDC).

The viewing head is powered by the P520 signal processor via 

a 0.25A self-resetting fuse. The power to the signal processor 

itself is via a 0.75A self- resetting fuse. These self-resetting 

fuses are re-set when power to the signal processor is 

removed. It is recommended that no more than four P520 

signal processors be supported by one 24VDC power supply, 

unless a method of redundancy is employed together with 

larger capacity power supplies. 

Other possible combinations can be used; for instance, the 

battery backup terminal could be used for redundancy. 

However, care must be taken with these redundant schemes 

to make sure that failure of the primary power supply won’t 

affect the backup power supply, as well.

It may be more economical to use larger-capacity power 

supplies for applications using twelve or more P520 signal 

processors.

For example: a power supply may power twelve P520 signal 

processors, each with one viewing head. Should the power 

supply fail, a redundant scheme utilizing two power supplies 

with “steering” rectifiers to prevent current from flowing into a 

failed power supply output would prevent the twelve flame 

monitors from being shut down.

Larger power supplies can be used with this redundant wiring 

scheme if there are more than twelve P520 signal processors 

in a system. Care should be taken when wiring multiple signal 

processors to ensure the selected bus wires will carry the 

current. The terminals on the rear PCB will accommodate a 

wire size up to 14AWG, allowing for relatively high currents.

There is a small processor in all viewing heads and it is 

possible that it could fail and produce erroneous viewing head 

pulses. The self-check circuitry guards against such an 

occurrence. There are several tasks that require intelligent 

interaction between the viewing heads and the signal 

processor. If all of the interactions do not occur properly, the 

viewing head will not send pulses back to the signal processor 

and the flame relay will open.

CABLE PN: C328

RED

WHITE

GREEN

BLACK

SHIELD

SIG

SC
+V

GND

SIG

GND

BLACK

RED

CONNECTOR BACK WIRING VIEW (FEMALE)

SIGNAL PROCESSOR

CONNECTION

M33281

SHIELD

GREEN

WHITE

USE SHRINK TUBING

CONNECTOR PROTECTOR 

SLEEVE (SUPPLIED)