Teledyne 6200E - Sulfides Analyzer - Manual (Page 236)

Theory Of Operation Model 6200E Instruction Manual
236 M6200E Rev: A1
DOS Shell
API FIRMWARE
Analyzer Operations
Calibration Procedures
Configuration Procedures
Autonomic Systems
Diagnostic Routines
Memory Handling
IDAS Records
Calibration Data
System Status Data
Interface Handling
Sensor input Data
Display Messages
Keypad
Analog Output Data
RS232 & RS485
External Digital I/O
Measurement
Algorithm
(H
2
S & SO
2
)
ANALYZER
HARDWARE
PC/104 BUS
PC/104 BUS
Figure 10-22: Basic Software Operation
10.7.1. Adaptive Filter
The M6200E H
2
S analyzer software processes sample gas measurement and reference data
through a built-in adaptive filter built into the software. Unlike other analyzers that average the
sensor output signal over a fixed time period, the M6200E calculates averages over a set number
of samples. During operation, the software automatically switches between two filters of different
lengths based on the conditions at hand.
During conditions of constant or nearly constant concentration the software computes an average
of the last 240 samples. This provides the calculation portion of the software with smooth stable
readings. If a rapid change in concentration is detected, the adaptive filter switches modes and
only averages the last 48 samples. This allows the analyzer to respond to the rapidly changing
concentration more quickly. Once triggered, the short filter remains engaged for a fixed time
period to prevent chattering.
Two conditions must be simultaneously met to switch to the short filter. First the instantaneous
concentration must exceed the average in the long filter by a fixed amount. Second, the
instantaneous concentration must exceed the average in the long filter by a portion, or
percentage, of the average in the long filter.
If necessary, the filter lengths of these two modes may be changed to any value between 1 and
1000 samples. Long sample lengths provide better signal to noise rejection, but poor response
times. Conversely shorter filter lengths result in poor signal to noise rejection, but quicker
response times.
10.7.2. Calibration - Slope and Offset
Calibration of the analyzer is performed exclusively in software. During instrument calibration
(Chapters 7 and 8) the user enters expected values for zero and span through the front panel
keypad and commands the instrument to make readings of sample gases with know
concentrations of H
2
S. The readings taken are adjusted, linearized, and compared to the expected
values as input. With this information the software computes values for instrument both slope and
offset and stores these values in memory for use in calculating the H
2
S concentration of the
sample gas.