Teledyne LGA-3500 - Laser Gas Analysis system - Manual (Page 45)

Laser Gas Analyzer Operation
Teledyne Analytical Instruments 31
• Con. output--20mA: gas concentration value corresponding to
20mA of the 4-20mA gas concentration output.
• System time: the time of system clock.
• System date: the date of system clock.
Note: The Model 3500 outputs average gas concentration at the
4-20mA gas concentration output port.
The computation method for average concentration and standard
deviation is described below:
Average Concentration
old cur new
g
N
g
N
g
⎟
⎠
⎞
⎜
⎝
⎛ −
+ =
1
1
1
Where:
new
g ——
Average concentration value
cur
g —— Current concentration value
old
g
—— the average concentration value before adding the
latest measurement
cur
g stored in the system memory
N
——Ave. times
The method is in equivalent to having the current concentration
value pass through a low-pass filter with a cut-off frequency at
τ π
N
f
2
1
=
, where
τ
is the time the system needs to finish one
measurement. Typically, the Model 3500 series instruments have τ set
at ∼1 second at the factory. However, it can also be set at any value in
the range of 0.1~1 second upon customer request to suit particular
applications that require faster response time. Contact technical support
for more information.
Normally, every time the system finishes one measurement cycle,
the LCD display and output at the 4-20mA output port refreshes.
Standard Deviation