Honeywell Stereo System P520 Manual De Usuario

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The P520 communicates with any host computer that has a 

USB port and supports ASCII character code transmission at 

4800 baud (or, in current revisions of the processor chip, at 

4800 or 9600 baud). The baud rate is displayed with the 

module address in the current versions (see SETTING 

ADDRESSES, section). The data transmitted to and from the 

P520 is over two twisted pairs that are differentially driven and 

received according to the RS-422 standard. The differential 

mode allows long wire runs in harsh, electrical environments. 

Honeywell offers a RS485/422 to USB converter to use in 

conjunction with the P520 signal processor. The Honeywell 

part number is COMMOD.

Modbus Communication protocol allows the P520 to 

communicate with open process controllers or human-

interface host computers that support this protocol. The P520 

processor status and settings are organized as 23 4X holding 

registers and five 0X discrete registers. For more information 

on Modbus protocol, please refer to Modicon’s Modbus 

Protocol Reference Guide (PI-MBUS-300 Rev E).

P520 can communicate only in Modbus RTU mode, with the 

following configuration:

• 9600 baud

• 8 data bits

• No parity

• 1 stop bit

The factory default of a P520 station number is 0. It is 

important to change the station number so that there are no 

duplicate stations in the network. 

No flame signal and no display.

1. Check the wiring between the signal processor and the viewing 

head. Refer to the Wiring the Rear PC Board section.

2. Using a volt meter check the voltage at PWR IN terminals with a 

volt meter. It should measure approximately 24VDC. If not, 

check the power supply and wiring, or replace the power supply.

3. If 24VDC is measured, remove the power for 10 seconds. If the 

self-resetting fuse has tripped, removing then reapplying power 

will reset the fuse.

Digital display shows 0000 and there is no flame signal.

1. Remove connector from viewing head and check wiring per 

Fig. 4 and 5.

2. Ensure the proper impedance resistor is in place (refer to Wiring 

of Viewing Head section). Using a volt meter, check the viewing 

head terminals on the P520, for 24VDC across +V and GND. If 

the voltage is low, check input voltage to the signal processor. If 

the input voltage is measured to be in spec, remove power and 

disconnect all connections to the viewing head(s). Wait 10 sec-

onds (which resets the self-resetting fuse) and then reapply 

power and re-measure voltage across +V and GND.

3. If voltage measures +24VDC (nominal) at the viewing head ter-

minals at the signal processor, turn off power to the signal pro-

cessor and using an ohmmeter check continuity of each cable 

wire from the signal processor terminals to the viewing head 

connector terminals. If cable continuity checks out, the viewing 

head may be defective.

Flame signal shows on display; flame on relay and light 

are off.

1. The viewing head is incorrectly wired, or defective (see above).

2. The set point values for flame ON are incorrect.

Flame signal shows on analog bar graph display; flame 

light is off; lockout light is on.

1. The viewing head may be defective.

2. There may be a noise or grounding problem. Check that equip-

ment is properly grounded and ensure good clean contact on all 

ground connections. Move viewing head and cable/conduit at 

least 12 inches (31 cm) away from any source of high powered 

switching (e.g. igniter equipment). Refer to Grounding and 

Shielding section.

3. Press the RESET button on the front panel.

The 1-9 LED stays on.

1. There may be a noise or grounding problem (see above and 

refer to Grounding and Shielding section).).

2. The viewing head may be defective.

The front panel buttons do not respond.

1. The P520 front panel may be locked out.

2. Signal processor may be in remote operation only mode.

3. Cycle power to the signal processor with the viewing head con-

nected.