Thermo Scientific SGD-O, User Manual

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Thermo Fisher Scientific SGD-O User Guide
7-1
Chapter 7
Adjusting the Gain Settings
Users of the SGD-O density gauge often move the detector assembly from
application to application. Among these different applications are variations
in sizes and schedules of pipes, as well as activity and ages of radioactive
sources. The gauge’s hardware gain settings are set for a particular
application; thus, it may be necessary to change certain jumpers or
components to set the detector within its allowable voltage range for the
current application.
This chapter explains how to set the gain values for the Fast Start Unit
(FSU) pre-amp board so that it can be used in different applications
without having to return it to the factory for modification.
Note
This chapter applies to the SGD-O FSU pre-amp board 885623 at
revision F or later.

Note
Before proceeding, verify that the R1 and R28 factory adjustments
have not been altered. If those adjustments are not set correctly, the gain
circuit will not function correctly. Reference the FSU troubleshooting
procedure in Chapter 9.

Warning
Ensure that power is off and the area is non-hazardous before
making any of the adjustments described in this document.

The R35 potentiometer (pot) is a fine tuning pot only. It was never
intended to be a full-scale adjustment. Therefore, if you cannot get the
detector output up to 9.6 Vdc by adjusting the R35 pot, with air in the
pipe, the hardware gain will have to be modified. A number of components
and jumpers on the pre-amp board can be adjusted in such instances.
Specifically, these are components C13, R5, R36, R37 and wire jumpers
W1, W2, and W3. See Figure 7–1 .
Overview
Components and
Jumpers