Emerson Rosemount 700XA Reference Manual page 16

Overview
June 2022
Figure 1-3: Detector output during component elution
A. Detector bridge balanced
B. Component begins to elute from column and is measured by thermistor.
C. Peak concentration of component
In addition to amplifying the differential signal developed between the two thermistors,
the preamplifier supplies drive current to the detector bridge.
The signal is proportional to the concentration of a component detected in the gas
sample. The preamplifier provides four different gain channels as well as compensation for
baseline drift.
The signals from the preamplifier are sent to the electronic assembly for component
concentration computation, recording, or viewing on a personal computer (PC) with
Rosemount MON2020.
1.4.2 Flame ionization detector (FID)
Another detector available for the Rosemount 700XA is the flame ionization detector
(FID).
The FID requires a polarization voltage, and its output is connected to the input with a high
impedance amplifier that is called an electrometer. The burner uses a mixture of hydrogen
and air to maintain the flame. The sample of gas to be measured is also injected into the
burner. See
16
Figure 1-4 for a schematic diagram of the FID.
Reference Manual
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