222 AO2000 CONTINUOUS GAS ANALYZERS | OI/AO2000-EN REV. B
Externally controlled calibration
Definition
Externally controlled calibration means: Zero-point and end-point value
alignment is triggered by control signals from an external control unit.
Test gas supply
The test gases should be supplied automatically by external solenoid valves
also controlled by the external control unit. The dew point of the test gases
must be approximately the same as the dew point of the sample gas.
Analyzer modules with several detectors
In analyzer modules with several detectors (e.g. Uras26) all detectors are
calibrated simultaneously.
Control signals for the externally controlled calibration
Control signal Level
1)
Digital input
3)
Zero alignment Edge Low → High
2)
DI3 "Status Signals/
Externally con-
trolled calibration"
Span alignment Edge Low → High
2)
DI4
Calibration cell in/out
4)
In: High, out: Low DI1 "Alarm values"
Hold current signal High DI2
1) Low level 0 to 3 V, High level 12 to 24 V
2) The Low → High transition may also be generated by an external con-
tact. After the transition the High level must be present for at least 1 s.
3) Standard function block applications (see page 112)
4) Uras26 analyzer module only
Requirements for the external control set-up
For the Caldos25, Caldos27, Magnos206, Magnos28 and Magnos27 analyzer
modules the external calibration control must be set up such that the zero-
point calibration always precedes end-point calibration.
The external control unit must produce the control signals for zero and span
alignment and for the external pneumatic components, e.g. solenoid valves
and pumps.
External control of calibration must be set up so that calibration starts only
if there is no "Error" or "Maintenance mode" status signal.
Also the external calibration control must allow for a purge time from the
point of gas switch-over until stabilization of the measurement value, i.e.
until the zero or span calibration is initiated. Depending on the length of the
gas paths in the gas analyzer and on the sample components involved, this
purge time can take several minutes.
To allow measurement values to stabilize, the "Hold current signal" control
signal should remain set for a specified time after calibration is finished.
Calibration data
Setting calibration data is described in section "Calibration data for exter-
nally controlled calibration" (see page 231).
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