Tyco MX4428 technical manual Photo Processing, Smartsense Processing, Smartsense Enhancement

MX4428 MXP Engineering / Technical Manual		Document: LT0273
MXP Loop Filter Board
9.4	PHOTO PROCESSING

9.4.1SMARTSENSE PROCESSING

The smoke reading of the detector is returned as input AI0 from the device ASIC. Figure 9.2 shows a general view of the processing of the values received from the photoelectric sensor. It is of interest that the value is multiplied by a factor (between 1 and 4) depending on the factory calibration of the sensor, and again multiplied by a factor depending on the temperature rate of rise (when “enhanced” operation is selected). In both cases the “tracked value” is subtracted, the multiplication applied, and the “tracked value” added back in. This is so that all scaling occurs relative to the clean air value.

When the MXP or detector powers up the clean air value or “tracked value” is initially set to the average of the reading from the detector after about 30 seconds and the value stored in the detector EEPROM, and then may continue to track up or down by 1 each poll for the next 3 minutes.

When the “tracked value” is reset manually by command from the MX4428, it is set to a value which will make CV equal to TV. Unless the calibration factor is exactly 1.0, the new TV is not simply the same as the previous CV.

Subtractor Comparator

		Calibration
			Exponential
	Subtractor	Adder	Filter
Raw
Value	+
	-

Enhancement Factor derived from Heat RORCV (1 if no enhancement)

Subtractor

+

-

+ + PreAlarm

- -

PreAlarm Threshold

CVEnh (CV to FIP)

Slope

AdderLimiter

Smoke Filter

Divisor

TV = Tracked Value = Assumed Clean Air Value

CV

Multiplier	Smoke Step
	Limit
		SLV
	Subtractor	Comparator
	+	+	Alarm
	-	-

Very Slow Slope
Limiter	Alarm Threshold
(1 step per Photo Tracking Interval)

Figure 9.2 Photo Processing Diagram - SmartSense

9.4.2SMARTSENSE ENHANCEMENT

Figure 9.3 shows the amount by which smoke readings are increased depending on the temperature rate of rise.

The default enhancement multiplier parameter is 12. The graph (Figure 9.3) shows the effect of this factor and also the effect of an alternative parameter of 6.

If enhancement is disabled, (or less efficiently if the enhancement multiplier parameter is set to 0) the multiplier is exactly 1.

Page 9-6 24 March 2006 Issue 1.5