Page 56 - International safety guide for oil tankers and terminals

INTERNATIONAL SAFETY GUIDE FOR OIL TANKERS AND TERMINALS

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Typical values
R1 = 1k R1
R2 = 1k Sensitive
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
RV1 = 50k element
(Detector)
V1 V2
Bridge supply Pellistors RV1
Non-sensitive
element
(Compensator)

R2

Output voltage
Cross section
of catalytic
element

Catalytic coating
ึ
Bead

Platinum wire

1 to 2 mm

Figure 2.1 – Simplified diagram of a flammable gas monitor incorporating a pellistor

2.4.3.2 Cautions
Poisons and Inhibitors
Some compounds can reduce the sensitivity of the pellistor.
Poisons – these are compounds that can permanently affect the
performance of the pellistor and include silicone vapours and organic
lead compounds.

Inhibitors – these compounds act in a very similar way to poisons,
except that the reaction is reversible. Inhibitors include hydrogen
sulphide, freons and chlorinated hydrocarbons. If the presence of
hydrogen sulphide is suspected, this should be tested for before any
measurements of hydrocarbon vapours are carried out. (See Section
2.3.6.)

Pressure
Pellistor type instruments should not have their sensors subjected to
pressure as this will damage the pellistor.

22 © ICS/OCIMF/IAPH 2006