Metek 920, Operator'S Manual With Essential Health And Safety Requirements

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4-68 | Model 920 Multi-Gas Analyzer
Probe Blow-Back Control (Optional)
For applications using the Probe Blow-Back function, it is enabled at
the factory (disables Temperature Zone 2).
The Probe Blow-Back control can be set up to be performed automatically,
at timed intervals, and for timed durations. This is done by setting the
Interval , Duration , and Pulse Width timers. After these timers have been
set, the analyzer will initiate a Probe Blow-Back at the preset intervals. See
Figure 4-8 for an example timing chart.
A Probe Blow-Back can also be started manually by the user, by pressing
F1 7 Ent (CAL mode). The manual Blow-Back function will perform one
cycle, determined by the Duration Timer setting (CAL mode, F3 3 ). To
abort a manual Blow-Back, press the Esc key.
The Probe Blow-Back control signal is available at terminals 3 (-)
and 4 (+) of J106 on the Termination board (also used as the SSR
control for a heated Vent Line or Sample Conditioning Unit). The
signal switches from 0 VDC to +15 VDC when the Probe Blow-Back
feature is activated.
The Probe Isolation signal is typically available at
terminals 5 (N) and 6 (L) of J105 on the Termination board. Refer to
Final “As-Built” drawings in the Documentation Package for termina-
tion points for your system.
Figure 4-9.
Probe Blow-Back
Timing Chart, example.
Sample Delay
(sec)
Probe Blow-back Duration (sec)
Probe Blow-back Pulse Width (sec)
Probe Blow-back Interval (min)
CAL
Rel
ay
Pr
obe
Is
ol
at
io
n
So
le
no
id
Pr
ob
e B
lo
w
-b
ac
k
A
ir S
ole
no
id
2x Probe Blow-back Pulse Width
NOTE: Illustration only. Not to scale.
Probe Blow-back Timing
12/31/2008 1

See also the
descriptions for F2 1 under
“RUN / CFG Mode – F2
Commands” and F3 3 under
“CAL Mode – F3 Commands”
in this chapter.

(PrbT) CAL

F3 3

NOTE

NOTE