Honeywell P520 Manual Do Utilizador

P520 SIGNAL PROCESSOR

66-2066—01

Fig. 3. Rear PCB terminal wiring.

Polarity must be observed when wiring this connection (the

positive terminal is on the top). This is an isolated input, so

two wires are required. Any DC voltage from 7.5 to 30 may be

used. The current required will depend upon the voltage,

because this is a photocoupler interface circuit with a 3900

ohm resistor feeding the LED light source.

For example: a 26VDC voltage will result in a current flow of

25/3900 =.0064 Amp.

If flame is being detected and the channels are switched, the

flame relay will remain energized for one cycle regardless of

the new set points, allowing channel changes “on the fly,” so to

speak. If the new flame OFF set point is equal to or greater

than the current signal count, then the flame relay will de-

energize on the subsequent cycle.

The remaining two-pin terminal designated REMOTE METER

(to the left of the V.H. SEL terminals) is for the remote meter

connection. This output is a current-driven signal that ranges

from 0 to 20mA for remote meters, and can be switched to a

range of 4 to 20mA (refer to section 4-20mA REMOTE

OUTPUT). Connect the terminal marked “positive” to the

positive meter terminal. This current signal can be used with a

volt meter by feeding the signal to a resistor connected to the

ground. The voltage developed across the resistor will follow

Ohm’s law V=IR.

For example: a 3-volt meter can be used with a resistor of 3/

.02 = 150 ohms, which will result in a full-scale reading of 3

volts for a 20mA output.

The terminals called TX+, TX-, RX+, and RX- (at the bottom of

the PCB) are used for the serial communication link. They are

also in pairs to accommodate “daisy chaining,” but the pairs

are arranged for twisted pairs instead of adjacent redundancy.

The serial communication is achieved by using ASCII

character code transmission at 4800 through the USB port on

the host computer. The P520 uses RS-422 data transmission

which is over two, twisted pairs that are differentially

transmitted and received, allowing long wire runs to be used

through noisy environments. A USB to RS422 converter must

be used to communicate with the P520, and the connections

are made to the terminals marked TX+, TX-, RX+ and RX-.

The transmitting, twisted pair goes to the TX terminals, and

the receiving, twisted pair goes to the RX terminals.

NOTE: The terms “transmit” and “receive” used here

with respect to the P520 will be reversed with

respect to the converter connection on the host

computer. Refer to later sections in this manual

for a detailed description of the software and

how it is to be used with the P520.

P520

F1/.75A

M33217

F2/.25A

P520

RELAYS

FLAME RELAY

SELF

CHECKING

RELAY

PWR IN

BAT +26VDC GND

RF C

OFF

RF C

OFF

RC C

GND

SIG

GND

REMOTE METER

V.H. SEL

CHAN SEL

TX+ TX- TX+ TX-

RX- RX+ RX- RX+