SRS Labs QMS 100 Series, User Manual

Page: 136 / 280

3-12 Programming the RGA ECU
SRS QMS Gas Analyzer
Please consult the RGA Command Set section for details on the CA command.
Detector Programming example
The following list of commands starts by checking the RGA ECU to make sure there is a multiplier
installed: A CDEM is present if a 1<LF><CR> response is sent back to the computer. After the test
(and assuming the CDEM option was detected), a voltage of -1400V is set across the multiplier, and
the noise floor setting is programmed for minimum averaging and maximum scan rate. The detector is
now fully configured for CDEM measurements with -1400 V of CDEM bias voltage.
MO? Multiplier Option Query. Check query response: 1<LF><CR> confirms CDEM option.
HV1400 High Voltage CDEM = 1400V. Echoes the STATUS Byte.
NF7 Noise Floor = 7. Echoes the STATUS Byte.
Notes :
Append a CA command at the end of this list to readjust the zero of the ion detector measurements
under the present detector settings. The correction factor will then be used by all measurements (i.e.
single mass and total pressure) under this same detector settings to correct against zero drifts. Use the
HV0 command to go back to FC detection mode.
Important: Total Pressure measurements are disallowed when the CDEM is activated (TP_Flag is
cleared as soon as the CDEM is biased). Please see the TP command for details.
Detector Programming Tips
•
Use the ElecMult LED to visually inspect the status of the CDEM during programming.
•
Use the HV? command to query the type of detector that is currently active. The CDEM is
active if a non-zero response is returned to the computer.
•
Check the value of STATUS as returned after the HV command execution: Bit 3 provides
immediate information about the success of the command.
•
The HV command checks for the presence of a CDEM option in the RGA ECU before
execution starts and an error is reported if no CDEM is available. (Please see EM query
command for details.)
•
It is possible to activate the CDEM if the filament is not emitting electrons, but the CDEM
will be deactivated by any overpressure that shuts-down the filament.
•
The correct operation of the electrometer can be tested using the Error Reporting command
ED?.
•
The scan rates and signal-to-noise ratios for the different NF settings of the electrometer are
listed in a table in the Electrometer section of the “RGA Electronics Control Unit” chapter.
•
When using the RGA Windows program to operate the RGA, the Scan Speed parameter
setting available in the Scan Parameter Setups of the Scan menu is used to set the NF
parameter value in the RGA ECU according to the equation:
NF = ScanSpeed - 1.
•
Use the CA command to readjust the zero of the detector every time the detector settings
are changed (i.e. after changing the NF parameter setting or changing detector type). This is
particularly important if the new settings have not been used in a long time or since the unit
was turned on or recalibrated with the CL command.