SRS Labs QMS 100 Series, Руководство пользователя

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3-36 RGA Command Set
SRS QMS Gas Analyzer
•
All offset correction factors previously stored in memory are cleared after a
complete calibration of the electrometer is performed (see CA command for
more information).
Parameters: Only one possible command format is allowed
CL
Error Checking:
An attempt to pass any parameter with CL results in a bad-parameter error being reported.
HVparam, param: 0 - 2490, *, ?
Description : Electron Multiplier High Voltage Bias setting.
Echo : STATUS error byte or Query Response.
Set a negative high voltage across the electron multiplier (CDEM), connect the CDEM signal output to the
electrometer and reconfigure the electrometer and current measurement algorithms to handle negative
electron currents. The parameter value represents the magnitude of the bias voltage in units of Volts.
Warning: This command only works in ECU’s with the CDEM option (Opt01) installed (See
MO command.)
Since the CDEM turns ion signals into amplified electron currents, the RGA ECU automatically
reconfigures the electrometer to measure negative currents when a finite biasing voltage is selected. The
current measurement algorithm is also automatically reconfigured so that the
magnitude of the currents
measured is transmitted over RS232. The host computer can then handle the amplified signals the same
way it did with the positive ion currents (i.e. it does not need to flip the sign of the currents received).
The HV_LED reflects the status of the CDEM bias at all times.
Since it takes time for the CDEM and for the electrometer to settle, completion of the command is
prompted to the host computer transmitting the STATUS byte value over RS232.
Important:
•
Faraday Cup detection is the default setting upon a power-on reset of the
RGA
ECU .
•
The voltage set by this command is the output of the high voltage power
supply. A 1MOhm resistor is placed between that output and the CDEM’s
cone. CDEM's typically have an internal resistance in the order of 100-2500
MOhm, and consequently the voltage measured on the CDEM will always
have a magnitude smaller than the value returned by a HV? command (i.e.
the CDEM becomes part of a voltage divider in conjunction with the 1MOhm
resistor).