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Model 400E Ozone Analyzer
Instruction Manual
10.3.4. Pneumatic Sensor Board
The pneumatic sensor board measures the absolute pressure of the sample gas up-
stream of the analyzer's critical flow orifice. This measurement is used in calculating
the O
concentration of the sample gas (see Section 10.1.1).
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Also a Flow Meter, also located up-stream of the critical flow orifice measure the
gas flow rate through the instrument.
The following TEST functions are viewable from the instrument's front panel:
1. Sample flow - reported in scc/min
2. Sample pressure - reported in in-Hg-Absolute
The M400E displays all pressures in inches of mercury-absolute (in-Hg-A). Absolute
pressure is the reading referenced to a vacuum or zero absolute pressure. This
method was chosen so that ambiguities of pressure relative to ambient pressure
can be avoided.
For example, if the vacuum reading is 25" Hg relative to room pressure at sea level
the absolute pressure would be 5" Hg. If the same absolute pressure was observed
at 5000 ft altitude where the atmospheric pressure was 5" lower, the relative
pressure would drop to 20" Hg, however the absolute pressure would remain the
same 5" Hg-A.
10.3.5. Relay Board
By actuating various switches and relays located on this board, the CPU controls the
status of other key components. The Relay Board receives instructions in the form
of digital signals over the I
its various switches and relays appropriately.
Heater Control
A heater is attached to the Photometer UV Lamp housing and controlled by solid
state relays located on the Relay Board.
On instruments with IZS Options installed, an additional heater also controlled by
the Relay board is attached to the IZS O
Valve Options
The solenoid valves of the Zero/Span/Cal Valve Option as well as the Sample/Cal
valve included with the IZS option are controlled by a set of electronic switches
located on the Relay Board. These switches, under CPU co ntrol, supply the +12VDC
needed to activate each valve's solenoid.
P/N 04316 Rev: B
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C bus, interprets these digital instructions and activates
Generator UV Lamp.
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THEORY OF OPERATION
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