42/24-10 EN Rev. 9
Chapter 8: Gas Analyzer Calibration
8-A-9
Externally Controlled Calibration
Definition
Externally controlled calibration means:
Zero and span value alignment is triggered by control signals from an external
control unit.
Test Gas Supply
The test gases should be started automatically by external solenoid valves also
controlled by the external control unit.
Test Gas Dew Point
The test gas dew point must be nearly identical to the sample gas dew point.
Analyzer Modules
with Multiple
Detectors
In analyzer modules with several detectors (e.g. the Uras26) all detectors are
calibrated simultaneously.
Control Signal
Level
1)
Input
Zero alignment
Low
→
High Edge
2)
DI3
Span alignment
Low
→
High Edge
2)
DI4
“Status signals / Externally
controlled calibration”
3)
Calibration cell in / out
4)
In: High, Out: Low
DI1
Externally Controlled
Calibration Control
Signals
Hold current signal
High
DI2
“Limit values”
3)
1) Low Level 0–3 V, High Level 12–24 V
2) The Low
→
High transition may also be generated by an external contact.
After the transition the High level must be present for at least 1 second.
3) Standard function block applications
4) Uras26 analyzer module only
External Control
Arrangement
For the Caldos25 , Caldos27 , Magnos206 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 gas components, e.g. solenoids 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 switchover 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 the calibration data is described on page 8-B-6.
