Alarm relay off timers
The 8 relays on the PCB are allowed to take time to de-energise.
For example, this delay could be used to keep fans running for a longer period after the
gas alarm to allow a larger area to be vented.
ENGINEERS menu 24 allows each of the 8 relays to be selected by using the UP (1) and
DOWN (5) buttons and then for each relay use the +(4) and -(2) buttons to change the
time for delay in increments of 1 second. The minimum time is 1 second.
Additionally, the first 16 external relays can also have a time delay for the pattern which
has been ouput by an event.
Pressing SELECT (3) will save the delay times in non volatile memory and return to the
ENGINEERS menu.
Voting relays
(Note these relays are also used with time weighted alarms)
ENGINEERING menu 25 allows channels to be assigned to a group voting system.
4 relays named OPTION 1-4 on the main PCB will be energised according to the voting
set up and de-energised when the alarms have subsided and after the relay off timer (set
earlier in section 24) has expired.
Using UP (1) and DOWN (5) to select the group, then use the + (4) and - (2) to select
how many alarms have to be active in this group to cause a relay to energise.
E.g. group 2 may have 5 sensors in its group and 3 alarms are required to energise relay
called OPTION2.
On entering menu 25, the direct 4-20 channels are displayed. UP (1) and DOWN (5)
buttons will display which groups this channel is in whilst the + (4) and - (2) buttons
change the channel being viewed. If a channel was in groups 1 and 3 then the display
would be 1-3-. If it was in groups 2, 3 and 4 then the display would be -234.
Pressing UP (1) or DOWN (5) changes this selection so keep pressing until the correct
grouping for your application appears. Any channel can be in all groups and this would be
displayed as 1234.
Pressing SELECT (3) presents the Addressable channels for a repeat of the above.
Groups can contain a mix of sensors from 4-20 direct or Addressable channels.
Time weighted alarms
Two types of time weighted alarms can be set using menu 31. STEL is a short time
exposure level which is a weighted average of gas level for the last 15 minutes. It is
associated with one of the four groups of sensors. Each group may have any number of
sensors within it and whichever is the highest reading in the group, this reading is used to
formulate the value of STEL.
LTEL is a long time exposure level taken over 8 hours and calculated in the same way as
STEL. Both STEL and LTEL have individual alarm settings but both act upon the same
relay. These alarms are rising only. Each gas within one of these 2 groups must clearly
be of the same type. If STEL or LTEL alarm level is set to a value greater than zero, then
this group becomes a TWA (Time Weighted Average) group and the voting function is
suppressed for that group.
21
