Stanford Research Systems RGA100, Operating Manual And Programming Reference

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Scan and Measurement Commands 6-45
SRS Residual Gas Analyzer
The number of points (ion currents) retuned over RS232 is calculated based on
the MI and MF parameter values. Number of points = MF - MI + 1. Each point
transmitted represents an ion current and as such corresponds to 4 bytes being
received by the host computer.
The HP query is used to verify that the RGA and the host computer agree on the
number of bytes that will be exchanged over RS232 during the histogram scan.
The total number of bytes sent out to the host computer during an histogram scan
is obtained multiplying by four the number returned by the HP query.
Parameters: This command is a query, and can only have one parameter format:
HP?
Error checking:
The only acceptable parameter is a question mark.
The absence of a parameter (i. e. HP) is treated as a Bad-Parameter error.
HSparam, param:0 - 255,*
Description : Histogram Scan Trigger.
Echo: Ion Currents.
Excecute one or multiple Histogram Scans under the present scan conditions.
The scan parameter can be set for single, multiple and continuous scanning
operation.
A Histogram Scan consists of as a succession of individual mass measurements
(see MR command) over a pre-specified mass range.
The mass range for the scan is set in advance with the commands MI (Initial
Mass) and MF (Final Mass). The type of detector and noise-floor settings to be
used during the scan must be selected in advance with the NF and HV
commands. 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).
Important:
x
Any command received by the RGA in the middle of a scan will immediately
stop the scan, halt transmission and clear the RGA’’s transmit buffer.
x
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.