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T400 Controller Facilities Manual

667/EB/20200/000 Page 15-13 Issue 9

15.9.1 DFM Timing

15.9.1(a) Option 1

The timing range of the DFM is 0 to 255 hours in 1 hour steps, although the normal

time is 9 or 18 hours. The programmed value may be changed via the handset using the

DFD command.

Figure 21.7 shows an example configuration sheet including selection of the DFM

time, the selection of inputs covered by DFM, and the action on DFM timeout.

15.9.1(b) Option 2

The inputs are assigned to one of eight groups. Each group is allocated to a separate

‘Stuck active’ and ‘Stuck inactive’ time.

The timer for each input resets when the Detector changes state. It is possible to

introduce up to four threshold limits (as shown in the example below), and if the timer

value is greater than the threshold, a fault is reported straight away.

Note that short DFM periods should not be introduced at the same time as demand is

expected to increase, but some time later to allow for the fact that the timer value may

already have been exceeded.

Each input will be individually timed and checked against the timeout value, The

timeout values are:

Stuck Active time.......1 to 254 minutes

Stuck Inactive time.....1 to 254 Hours

The DFM Group times can be adjusted by the handset subject to configured limits for

the Active and Inactive times.

Additional Handset commands are available for this facility, see T400 Handset

Handbook 667/HH/20200/000

EXAMPLE:

Timeset A Timeset B Timeset C Timeset D

AIAIAIAI

DFM Group 0 60 2 30 4 30 4 30 4

DFM Group 1 30 9 30 18 15 9 255 255

etc....

In the above example:

‘A’ is the Active State (Measured in minutes).

‘I’ is the Inactive State (Measured in hours).

The DFM will time out for detectors in Group 0 during time set A as follows:

1 2 ... 148 149 150 151 152 153 154 155 156 157 158 ... 307 308

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