Stanford Research Systems RGA100, Operating Manual And Programming Reference

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6-40 Detection Control Commands
SRS Residual Gas Analyzer
x
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 heads with the CDEM option
(Option 01) installed (See MO command.)
Since the CDEM turns ion signals into amplified electron currents, the RGA head
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:
x
Faraday Cup detection is the default setting upon a power-on reset of the
RGA head.
x
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).