Tyco MX4428 technical manual DIM Processing, Load Graph, DIM Model, Vol, Input Condition Mode

= 137000 / (560 + 4700) = 26

MX4428 MXP Engineering / Technical Manual		Document: LT0273
MXP Loop Filter Board
9.8	DIM PROCESSING

9.8.1LOAD GRAPH

Figure 9.8 shows the V / I characteristics for the DIM detector terminals, together with the fault and alarm thresholds when using the default parameters. The shaded areas show the region of uncertainty.

Three lines are shown for three supply voltages.

	30		4k7 EOL
	25	T
		L	L
		U
tage	20	A	A
		F	M
			R
		O					M
Vol
	15	N			A	R		28V
				L
								24V
Load			A
	10							19V
	5
	0
		0	10					20	30	40	50

Load Current (mA)

Figure 9.8 DIM LoadLine Characteristics

9.8.2DIM MODEL

The reading from the DIM module can be modelled using the following method. Calculate “R” from a point on the load line = Load Voltage / Load Current. Reading = 137000 / (560 + R)

For example take the point where the 4k7 EOL resistor crosses the 24V line.

R = 20.8 / .0044 = 4700

Reading

Note that for a given “R”, the reading is independent of the supply voltage.

9.8.3ALGORITHM - DIM800

The unverified input condition is evaluated according to the following table, depending on the values of parameters P1, P2, and P4. (if P4 is 0, assume it is 225).

Input		Condition (Mode 0)
P4	<= reading <= 255	Alarm
P1	<= reading < P4	Alarm
P2	<= reading < P1	Normal
0 <= reading < P2		Open circuit fault

Condition (Mode 1)

Short

Alarm

Normal

Open circuit fault

Changes in these states are verified as described in section 9.22.

Page 9-12 24 March 2006 Issue 1.5