IRIS P522 manual 4-20mAREMOTE OUTPUT, Flame Failure Response, Time F.F.R.T, Output

IRIS MODEL P522 APPLICATION MANUAL

lecting the set points. For instance, selecting a flame	4-20mA REMOTE OUTPUT
out set point that is equal to or greater than the flame	The standard remote meter output has a 0-20mA
on set point will result in this error indication.
	range and is designed to drive remote meters, as ex-
As well, the set points can be selected remotely through	plained earlier in this manual. You can convert this
	output to a 4-20mA range, as follows:
the serial communication port using a host computer –
explained in greater detail later in this manual.	Press the front panel push-buttons (indicated
FLAME FAILURE RESPONSE	in the table below) while holding down both
TIME (F.F.R.T.)	the Ý and ß buttons. Press all in each row
	together (i.e., three in the first row, two in
The flame failure response time, or F.F.R.T., is de-
	the second row, and three in the last row).
fined as the time it takes for the flame relay to de-
energize after the flame signal (from the viewing
	FLAME	FLAME	GAIN SET	FFRT	TIME DEL
head) drops out. This time delay is programmable
	ON	OFF			ON
from both the front panel of the P522 and a remote,
host computer. Only three settings are possible: one,	X	X	X
two and three seconds.
				X	X
The maximum time delay is limited to three seconds
in compliance with the FM (Factory Mutual) limit	X	X	X
of the F.F.R.T. to not more than four seconds.
The P522 decision-making process occurs on a pe-	FIGURE 6 - REMOTE METER ANALOG
			OUTPUT
riodic basis, and the decision to start a F.F.R.T. time
delay before de-energizing the flame relay is initi-	Doing this toggles the function back and forth be-
ated every second in step with the sampling rate of
	tween the 0-20mA and 4-20mA ranges.
the flame signal. This means that the actual flame
out condition (i.e., drop-out of the flame signal from	The change will be verified by four dashes “----”
the viewing head) will, in all probability, occur dur-	and “4-20” momentarily displayed. If the module is
ing the sampling period that causes the actual	programmed for the 4-20mA range, “4-20” will be
F.F.R.T. to be greater than the set time.	displayed; toggling back to the 0-20mA range will
For example: suppose the signal from	again cause four dashes to appear on power-up of
	the unit. Tha factory default setting are 4-20.
the viewing head drops out immedi-
ately after a sampling from the P522,	One thing to consider when feeding the 4-20mA sig-
and the sampling perceives flame to	nal to a remote computer or DCS, is that there is no
be present. If the F.F.R.T. set point is	isolation between the P522 ground and the remote
set for three seconds, there will be an	system ground. If there is a ground potential differ-
actual time delay of nearly four sec-	ence between the two systems, then there could be
onds. In other words, the actual	serious noise and performance problems. You will
F.F.R.T. will be the current set-point	not encounter this problem when using a remote
time, plus an additional amount of	meter by itself, because it will not be tied into an-
time not exceeding one second, de-	other electrical system (will not be sharing grounds).
pending upon when the flame signal	The bargraph reading on the front panel will not be
from the viewing head drops out.
	affected by this change to 4-20mA output. It will re-
	main the same as before (i.e., go to zero on no signal

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