Stanford Research Systems RGA100, Operating Manual And Programming Reference

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Built-in Hardware Checks 9-11
SRS Residual Gas Analyzer
Power-on check?: Yes
Ion currents from the Faraday Cup or the electron multiplier are measured with a very
sensitive logarithmic electrometer. The voltage levels are digitized with a 16 bit analog-
to-digital converter (ADC16) and turned into current values using a digital logarithmic
interpolation algorithm that calculate the currents from an internal calibration curve.
The Electrometer/ADC16 system is automatically tested by the firmware on power-on
and can be checked at any time with the query command: ED?.
Several tests are performed during the check:
1. The ADC16 input is grounded and its digital output is measured to make sure it
corresponds to less than 15 mV.
2. A current of +5nA is injected into the electrometer and the output is read and
compared to expected values.
3. The same test is repeated with -5 nA of input current.
If an error is detected: Bit 5 of STATUS is set, DET_ERR is updated, and the Error LED
is turned on. The detector is reconfigured to its pre-check configuration once the tests are
over.
Quadrupole Mass Filter RF P/S
STATUS Bit affected: 4
Error Byte affected: QMF_ERR
Error Reporting Command: EQ?
Error Codes prefix: RF
Power-on check?: Yes
The RF power supply that biases the rods of the Quadrupole Mass Filter is thoroughly
checked upon a power-on reset and can be tested at any time using the query command:
EQ?.
The RF amplitude is set at the level corresponding to the maximum mass value for the
head (100 amu for RGA100, 200 amu for RGA200 and 300 amu for RGA300) and the
following tests are done:
x
The voltage on the primary of the RF transformer is checked to make sure it is at
least 2V lower than the DC voltage used to power the instrument.
x
The amount of current flowing through the primary of the transformer is checked to
make sure it is less than 2.0 Amps.
x
RF_PRI is also checked (against RF_SET) to make sure the driver is not in current
limiting mode.