Tyco MX4428 technical manual Ionisation Processing, Ionisation Detector Processing

Document: LT0273	MX4428 MXP Engineering / Technical Manual
	Device Processing
9.6	IONISATION PROCESSING

The smoke reading of the detector is returned in two parts as inputs AI0 and AI1 of the device ASIC. In the MXP the average value of AI0 and AI1 is used for all calculations, so that all returned values to the MX4428 lie within the range of 0 – 255. (Note that TEPG literature refers to the sum of the two inputs.)

The processing is shown in Figure 9.6. The tracked value is initialised by setting it to a high value (100) when the MXP or detector powers up, and allowing the tracked value to increment / decrement by 1 for each of the first 4 minutes.

Subtractor Comparator

+ + PreAlarm

- -

PreAlarm Threshold

	Exponential
	Filter
Raw	CV
Value
	Filter Divisor

Slope
Limiter		Subtractor	Comparator
	SLV	+	+	Alarm
		-	-

Step Limit

Alarm Threshold

TV = Tracked Value

= Assumed Clean Air Value

Very Slow Slope Limiter

(1 step per Tracking Interval)

Figure 9.6 Ionisation Detector Processing

Issue 1.5 24 March 2006 Page 9-9