Honeywell Stereo System P520 Manual De Usuario

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66-2066—01

3. Install a ground wire from the ignition transformer case 

to the igniter assembly.

4. Ensure all igniter wires and cables show no signs of 

wear. Replace any igniter cables or wires that are frayed 

or cracked.

5. The viewing head must be electrically isolated from the 

burner front. 

a. Electrical isolation can be accomplished by install-

ing an Ultem nipple or an Ultem locking coupler 

adapter in conjunction with a locking coupler 

between the viewing head flange and the burner 

mount.

b. The purge air line should also be isolated from the 

viewing head. This can be accomplished by install-

ing any insulating material, for example a rubber 

hose, in between the purge air line and the viewing 

head.

6. On the terminals going to the viewing heads on the back 

of the P520, the terminals marked GND go to pin 5 of 

the S5XX and S55XB viewing head plug and to the des-

ignated ground pin for the S55XBE viewing head plug. 

Pin 5 of the S5XX and S55XB and the ground pin for the 

S55XBE viewing head male receptacles have an inter-

nal tab that grounds this connection to the viewing head 

housing. The terminal marked GND connects to the 

chassis ground of the P520. This ground is made 

through the internal PCB to the metal base of the P520. 

It is important that good grounding practices be followed when 

connecting power supplies. Interference problems can occur if 

the power supply chassis and the P520 chassis are at a 

different ground potential than the viewing head housing, 

which will be at a ground potential associated with the burner 

front. In these situations, the Honeywell viewing head 

effectively supplies a plant ground between the burner front 

and the panel enclosure. If there is a large potential difference 

between these points, considerable current can flow through 

the viewing head cable, which can, in turn, damage the P520 

signal processor or the associated power supply.

Four card guides are required for each P520 module; 

therefore, a total of sixteen card guides would be required to 

mount four P520 modules. Card guides are available as off 

the shelf parts and are not available from Honeywell.

The resulting rack will require spacers for the top and bottom 

of the rear backplane PCB. Card guides are required as well 

for installation. Spacers and card guides are available from 

electronic vendors and are not available from Honeywell.

A half-card frame, or “half rack” (9.5 inches wide) may be used 

as an alternative to the 19-inch card frame. A half rack will 

mount two P520 modules. 

A diagram of the rear backplane circuit board is shown in Fig. 

1. The relay outputs are located on the nine-contact terminal 

block located on the upper right of the board

RC C refers to the common terminal of the self-checking relay. 

There is only one pair of contacts used for the self-checking 

function. Here, the designation ON refers to the self-checking 

taking place in a normal manner. OFF indicates a failure in the 

viewing head or processor resulting from

- the internal or external hardware

- electronic critical component failure

- the power to the unit is OFF – the most likely condition

The horizontal set of six terminals (top left) is used for the 

main power into this plug-in module (PWR IN). Each 

designated terminal is a double terminal, or pair, so that the 

wiring from the power supply can be “daisy chained” from one 

P520 to the next without having to twist wires together into 

one termination.

The pair designated BAT is for battery backup, if used. The 

backup battery, if used, should be 24 volts, to ensure that the 

24VDC power feeding the P520 will not feed back into the 

battery. In other words, no current will flow from the battery as 

long as voltage of the main power supply is above that of the 

battery. The negative side of the battery goes to the GND 

terminal on the right.

Fig. 1 shows how these terminals are connected inside the 

P520. Note the two fuses marked F1 and F2. F1 is the main 

power fuse for the signal processor as well as the viewing 

head(s), and is rated at .75 Amp. Fuse F2 feeds only to the 

viewing head(s), and is rated at .25 Amp. Each viewing head 

draws about 100mA, so this output can supply up to two 

viewing heads. On all currently manufactured units, these 

fuses are self-resetting types, and will recover from an 

overload automatically after power is removed from the P520 

for 10 seconds.

Just below the six-pin PWR IN terminals are two, five-pin 

vertically-mounted viewing head terminals identified as V.H. A. 

and V.H. B. If only one viewing head is used, you must wire to 

the V.H. A. terminals. Below the V.H. A. terminals are two 

terminals marked V.H. SEL (viewing head selector relay). 

Energizing this connection with 24VDC will cause the relay on 

this PCB to switch to viewing head B.

Only the viewing head signal wire (SIG) and the signal ground 

wire (SIG GND) are switched with this changeover relay; the 

24VDC and power ground circuit is not disturbed. Make sure 

that the viewing head signal wire and signal ground (braided 

shield in the four-conductor cable) are both connected, 

because this ground connection is the only return path for the 

signal and self-checking circuit. The 24VDC used to switch 

this relay can be connected without regard to polarity. The two 

terminals marked V.H. SEL go directly to the relay coil.

The two-pin terminal to the right of V.H. SEL designated 

CHAN SEL is used for selecting channel A or channel B on 

the P520. Energizing this pair of terminals causes the B 

channel to be selected.