SRS Labs QMS 100 Series, User Manual

Page: 139 / 280

Programming the RGA ECU 3-15
Technical Reference
Histogram scans are triggered with the HS command. The scan parameter can be set for single, multiple
and continuous scanning operation. The mass range for the scan is set in advance with the commands
MI (Initial Mass) and MF (Final Mass). A current value is transmitted for each integer mass value
between MI and MF for a total of (MF-MI +1) measurements (See HP command). For maximum data
throughput, ion currents are represented as integers in units of 10
-16
Amps, and transmitted directly in
hex format (four byte integers, 2’s complement format, Least Significant Byte first).
The detector settings (i.e. detector type and electrometer’s noise-floor setting) to be used during the
scans must be selected in advance with the NF and HV commands. The zero of the RGA’s ion detector
is automatically readjusted at the beginning of each histogram scan so that the baseline is centered
around zero. The offset correction factor calculated and stored in memory, will then be automatically
used to correct all currents measured (i.e. including those from single mass and total pressure
measurements) under the same detector settings.
The internal scan parameters used by the firmware to step the RF during the scan, are checked and
corrected at the beginning of the scan to make sure that the correct RF levels (i.e. as specified by the
last Peak Tuning procedure) are programmed on the RF rods as a function of mass.
Important
•
The detector’s zero and the internal scan parameters are checked and corrected at the
beginning of each scan resulting in a slight delay before the scan actually starts.
•
The measurements are performed with the detector that is active at the time the scan is
triggered.
•
A Total Pressure measurement is performed at the end of each scan and transmitted out to
the host computer. In the event where the CDEM is turned on, the total pressure returned
from the ECU is 0.00. (Please see AP and TP Commands).
Setting up a histogram scan
The following list of commands sets a scanning range of 1 to 50 amu and the slowest scan rate, and,
after checking the number of currents to be measured per scan (not including total pressure), it triggers a
single scan under those conditions. During the scan, 50 scan currents and one total pressure current are
transmitted to the computer, and each current is 4 bytes long.
MI1 Initial mass=1 amu.
MF50 Final mass=50 amu
NF0 Slowest scan rate selected.
HP? Histogram Points query. The number 50 is echoed. Add one for total pressure.
HS1 Histogram Scan trigger: 1 scan is collected and transmitted.
Histogram Scan Programming Tips
•
It is good programming practice to follow each command that sets a parameter with a query
of the parameter setting. For example, the first command in the list should be followed by a
MI?, and a number 1 should be echoed by the RGA.
•
Notice that MI and MF are shared by analog and histogram scans.