NORMAL OPERATION
Touchpoint Pro
Pt. No. 2400M2566_1_EN
39
Operating Manual
6 Alarms, Faults, Warnings and Inhibits
TPPR may be set up to monitor many types of alarms in different areas of your site or sites. They may also be set up to
react in different ways, such as:
•
'Latched' or 'Unlatched' alarms
•
Short Term and Long Term Exposure Limits (STEL / LTEL) alarms
•
Rate Alarm
•
Activation of Relay Outputs
•
Voting / Non-voting alarms
•
Digital Inputs configured as alarms
6.1
Latching Alarms
During TPPR manufacture of Configuration the alarm channels will have been set as
Latched
or
Unlatched
. The default is
usually
Latched
, but this can be changed if required.
Unlatched alarms self-reset once the hazard has cleared, while latched alarms require the user to verify that conditions are
safe/normal before manually resetting the alarm.
The STEL alarm can be configured as latching or non-latching. STEL alarms should normally be set to latched to capture the
event until it is acknowledged.
The STEL alarm can only be reset when TPPR has calculated that the average gas level over the STEL Time Interval has
fallen below the STEL Alarm Level. Therefore, it will take a certain time before the STEL alarm can be reset even though
there may no longer be gas present. The length of time before reset is possible depends upon the historic and current gas
concentration/time relationship. If set to non-latching, the STEL alarm indication will persist until the average gas level over
the STEL Time Interval has fallen below the STEL Alarm Level. See the next section for more detail.
6.2
STEL / LTEL Alarms
Short Term Exposure Limits (STEL) and Long Term Exposure Limits are the toxic limits that the human body can tolerate
without suffering acute or chronic distress, injury, illness or disease. These figures will vary with every chemical or gas, and
they may vary again as more advanced and long-term laboratory testing produces new results.
TPPR uses analogue gas sensors to detect and record ambient toxic gas concentrations for STEL/LTEL. These readings
have two functions: firstly a rise in gas concentration above a pre-set STEL base rate will trigger the STEL alarm and
secondly a prolonged gas concentration above a pre-set LTEL base rate averaged over a period of time will trigger the LTEL
alarm.
TPPR averages STEL gas levels every ½ minute over user-determined rolling periods ranging from 5 to 60 minutes and, for
LTEL, continuously rolling periods of 10 minutes fixed at 8-hours total; i.e. 8 hours being the standard shift length.
Full details of STEL/LTEL theory and limitations are given in
Ch.9 STEL and LTEL Alarm Configuration,
and details on
setting it up are given in
Ch. 6 Software setup and Commissioning.
6.2.1
Using the STEL Alarm
Use the short term exposure limit (STEL) feature to indicate if a gas sensor is detecting an average level of gas that will
result in a hazardous situation.
The STEL feature continuously calculates the average gas level over time using a user selectable time period (STEL Time
Interval). An alarm will be indicated if the average gas level exceeds a user selected limit (STEL Alarm Level) within the
STEL Time Interval.
STEL alarm functionality is normally associated with personal gas detection equipment where it will give information about
an individual’s exposure to a hazard. As TPPR and associated sensors are fixed equipment, the user must consider how the
STEL feature is to be used as it is the sensor and not an individual that is exposed to gas.
CAUTION
In some countries, the use of a STEL alarm with fixed gas detection equipment is not recommended.
Refer to local and national regulations for further information.
