Thermo Scientific SGD-O, User Manual

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Adjusting the Gain Settings
Gain Control Settings
7-4
SGD-O User Guide Thermo Fisher Scientific
The gain settings listed in Table 7–2 are based on the following component
values being installed on the FSU pre-amp board.
●
R5 = 49.9 kohm, 1% precision
●
R36 = 8.25 kohm, 1% precision
●
R37 = 49.9 kohm, 1% precision
●
C13 = 330 pF
Note
On the three solder points of the W1/W2 jumper points, the center
point is the common. Therefore, the wire jumper goes from the center
point up to the 1 point for the W1 jumper or from the center point down
to the 2 point for the W2 jumper.

Install the proper gain components until the R35 pot will adjust the voltage
output of the detector, with air in the pipe, to 9.6 Vdc. As an example, the
R35 pot should adjust the voltage out from 10 Vdc to approximately 8.0
Vdc. If the R35 pot will only adjust the detector output from 4.0 to 5.0
Vdc, you will need to double the gain.
If you are already on the lowest gain and the voltage will not go down, the
factory pot settings may have been changed. Verify the R1 and R28 factory
settings.
Changing C13 will move the entire gain curve either up or down
depending on the capacitor used. Figure 7–3 shows the relationship C13
has in the control circuit of the FSU detector.
Table 7–2.
Gain settings
Times Setting Comment
Unity gain
(no gain)
No jumpers This may be necessary on 3” or 4” pipes with
newer sources to prevent saturating the
detector.
X1 W1 jumper This is the normal setting and adds a preset
amount of gain to the circuit over the unity gain
(no jumper) setting.
X1.5 W1 W3
R36 changed to 49.9 kohm
The W1 jumper puts R5, R37 in parallel with
W3 installed. Changing R36 changes the current
of the feedback loop to the op-amp.
X2 W2 jumper This leaves the W5 leg at 49.9K but puts R37
into the feedback loop, changing the current to
the op-amp.
X3 W2 W3
R36 changed to 49.9 kohm
This leaves the W5 leg at 49.9K and puts R36
and R37 in parallel, changing the current to the
op-amp.