Axis BTA 2100D Manual do Operador descarregar pdf (Página 87)

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The Electron Multiplier Tune will determine three proper settings: the Integrator

Zero, the 10

gain for the Electron Multiplier and the Electron Multiplier voltage

boost for optimum peak intensity and resolution.

The Integrator Zero Set obtains the average value of the signal level coming

from the Integrator Circuitry when the filament is off. When the filament is off, the

major source of signal coming from this circuitry is electronic noise. The

Integrator zero is adjusted such that the average value of electronic noise is

slightly greater than zero.

NOTE: The average value for the integrator zero; it should be between 0.20 and

0.80 counts. The Setting can range between 0 and 255.

The Electron Multiplier Tune program can automatically set the electron

multiplier voltage, such that the electron multiplier gain is approximately 10

electrons per ion. The program to set the electron multiplier voltage should only

be run when there is no sample of any kind in the instrument. For example, you

should wait at least 30 minutes after you close the calibration compound valve

before you run the program.

For the determination of 10

gain, Electron Multiplier Tune program runs in two

phases. In the first phase, the electron multiplier is set to a low test voltage, the

message PRE-ADJUSTMENT PHASE is displayed. The electron multiplier

voltage is increased by 100V increments until a signal is detected coming from

the electron multiplier. The electron multiplier voltage is then set to 300V less

than the value at which a signal was first detected. This ends the first phase.

In the second phase of the program, the electron multiplier voltage is increased

by 100V increments beginning with the final value of the first phase of the

program. In this phase, the Locate Low Voltage End where 10

gain is not

achieved and Locate High Voltage Start where 10

gain is exceeded.

NOTE: The electron multiplier is approaching the end of its lifetime when the

voltage setting nears 3000 volts.

The final determination is the Electron Multiplier boost, which determines the EM

voltage and AGC Target value for optimum peak intensity and resolution. It uses

the calibration compound peak at mass 131. The program adjusts the target TIC

value to a level that provides reasonable resolution of the major peak and its first

isotope peak. The program determines the height and area of the major peak of

interest, the height and area of the isotope peak, the height of the valley between

the two peaks, and ratio of the height of the valley and the height of the isotope

peak. The Final Gain setting will reflect any increase in the voltage for optimal

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