Honeywell Stereo System P520 User Manual

7

66-2066—01

Verifying the validity of the gain code received is one of the 

tasks performed by the processor in the viewing heads. The 

self-check pulse from the signal processors is a 100ms-wide, 

20V to 24V pulse with two notches or breaks in it. The position 

of each of the two notches communicates a gain code one to 

nine plus parity to the viewing head. The viewing head sends 

back an ID pulse in the first half of the 100ms self-check time. 

One viewing head expects to receive data with one parity and 

the other expects to receive data with the other parity. If a 

viewing head does not receive its correct parity plus the gain 

code once per second, it produces no output pulses.

Once the power is connected (24VDC) to the proper terminal, 

the P520 signal processor will be operational. There is no ON/

OFF switch on the P520; the moment it is powered on, it will 

reset and initialize. The self-checking light will start flashing, 

and one of the channel LEDs (A or B) will light (A will be ON if 

the channel select input at the plug-in connector is de-

energized). Ensure that the voltage is 24 to 26VDC. The P520 

signal processor will be reset when the power is turned on.

The P520 has been designed to deal with any foreseeable 

power failure or anomaly.

For example: if the power goes off while you are in the 

process of storing a set point (either from the front panel or 

from the remote, host computer), the internal power monitor 

circuit will signal the P520 signal processor to complete the 

store function before shutting down in an orderly manner. This 

prevents invalid data from being stored and protects existing 

data in the EEPROM (Electrically Erasable Programmable 

Read Only Memory) from corruption. This shut down process 

is facilitated by a special internal power supply that provides 

power just long enough to allow the processor to perform the 

shut down.

This internal circuit monitors the 24VDC power feeding the 

P520 signal processor, and when the voltage drops to about 

19 volts, the processor shuts down, the program stops 

running, and the self-checking function ceases (the self-

checking relay de-energizes). The blinking, SELF-CHECK 

O.K. light on the front panel will go out, and the flame relay will 

de-energize. 

Note that the earlier S509 and S512 viewing heads will shut 

down at about 17.0 volts; these viewing heads have their own 

power-monitoring capability, and will shut down on their own, 

independent of the signal processor.

When the power feeding the P520 exceeds 19 volts, the 

program is re-started. The SELF-CHECK O.K. light will start 

blinking, and the self-check relay will energize. If flame is 

present and a S509 or S512 viewing head is being used, the 

flame signal will not come back on until the power reaches 

21.5 volts. This can cause a lockout condition if the viewing 

head turns on during the dark period (defined by the periodic 

self-check signal going to the viewing head each second), 

requiring a manual reset of the P520. There is a 20 per cent 

probability that a lockout will occur because of the duty cycle 

of the self-check function (200 mSEC on and 800 mSEC off). 

The S506 and S511 do not incorporate the power-monitoring 

shutdown function, and will not cause a lockout condition.

These design precautions ensure that there will never be an 

unsafe situation created by abnormal line power (115VAC) 

conditions. The 26VDC power is very unlikely to come on 

gradually, but, if this did occur, the P520 would not get a 

proper reset. So, there is another function in the micro-

processor (used in the P520), implemented by circuitry and 

software, that causes the P520 to appear dead (i.e., the front 

panel will be dark) and to stay this way until the power is 

recycled in an abrupt manner, initiating the reset.

There are 16 set points stored in memory in the P520, divided 

into two equal sets, A and B.  The 5 items listed in Table 2 can 

be accessed directly from the buttons on the face of the signal 

processor per the instructions below.

To review any of the currently stored set points for the 5 items 

above, push the related button on front of the P522. For 

instance, to determine the current FLAME ON set point, press 

the FLAME ON button. The set point will be displayed on the 

readout for about four seconds, then the display will return to 

normal. The set points displayed will be for the channel that is 

active, which is indicated by a steady illumination of push-

button A or B.

To review the set points for the other channel, first select the 

channel (A or B), then press the related set point button.

For example: if channel A is already ON, indicating it is 

functional, and B is pressed, A will go out and B will proceed 

to flash slowly, indicating that further action is required. If A is 

already ON and A is pressed, it will stay steady ON and start 

to blink rapidly after any of the five set point buttons listed 

above are pressed.

In all cases, A or B will rapidly blink after the set point is 

selected. This action serves to alert the user that the current 

display is no longer that of the flame signal, and further action 

is required.

The fact that A or B is already on has nothing to do with the 

process of viewing the current set points, except that you do 

not have to select the channel if it is already on. The steady 

illumination of A or B indicates which channel is functionally 

active, and is selected at the terminals marked CHAN SEL.

At any time, you can press the reset button causing the P520 

signal processor to return to normal operation. The reset 

button is also used for resetting the lockout condition as 

explained in the section Self-checking Function.

Additionally, the viewing head temperature can be viewed by 

pressing the reset and down arrow button simultaneously.

Changing any of the five set points shown in Table 2 can be 

accomplished by selecting the set point via its button on the 

control face and using the UP or DOWN arrow buttons to 

FLAME ON

4 DIGIT NUMBER 0001-2999

FLAME OFF

4 DIGIT NUMBER 0000-2999

GAIN SET

2 DIGIT NUMBER 00-99

F.F.R.T.

1 DIGIT NUMBER 1, 2 OR 3

TIME DELAY ON 1 DIGIT NUMBER 0,1, 2 OR 3