CONFIGURATION
Part. No. 2400M2501_6 Touchpoint Pro
93 Technical Handbook
10.1.1 STEL Algorithm
TPPR calculates the moving half-minute time-weighted average (HM_TWA) of the selected STEL time interval as:
STEL = (HM_TWA1 + HM_TWA2 + HM_TWA3 → + HM_TWAN) / STELN
Where:
HM_TWA1 = 1
st
Half Minute TWA
HM_TWA2 = 2
nd
Half Minute TWA
HM_TWAN = N
th
Half Minute TWA
STELN – Number of Half Minute TWA Samples received in the chosen STEL interval (1a – 1g above)
The CCB then uses the resulting half-minute TWA for STEL moving average calculations:
HM_TWA = (GC1 + GC2 + GC3 → + GCN) / N
Where:
HM_TWA = Half Minute TWA
GC1 = 1
st
Gas Concentration Sample
GC2 = 2
nd
Gas Concentration Sample
GCN = N
th
Gas Concentration Sample
N = Number of Samples received in half Minute
10.2 LTEL Operation
The controller takes four gas readings every second. Readings are rolled up and averaged over the LTEL interval, which is
fixed at 8 hours.
The averaged LTEL value is updated every ten minutes and compared against the programmed LTEL limit.
The LTEL alarm is activated if the calculated result is above the programmed threshold.
Once started, the average is calculated continuously while the system is powered.
The averaged value is initialised to a default value:
when power is applied
when there is a change in LTEL configuration
when the alarm is reset by a user
The default value is equal to the Gas Range (Min) configured for the channel.
When the channel is inhibited, the controller continues to calculate the average but uses the above default value instead of
the sensor value. The channel will not alarm while inhibited.
The alarm cannot be reset until the current gas level reported by the sensor is below the programmed LTEL alarm level. The
time to wait before you can reset will depend upon the degree of ventilation and the residual gas levels.
WARNING
STEL AND LTEL HISTORY IS RESET WHEN POWER IS REMOVED. THE READING WILL REQUIRE AN
INITIALIZATION TIME AFTER POWER IS RESTORED.
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