|
CATALYTIC GAS SENSORS
(PELLISTORS) FOR FIXED INSTRUMENTS |
|
Part No. |
Bridge Voltage |
Bridge Current |
Min Output
|
Brief Description |
|
|
NP-30 |
2V
|
300mA
|
18mV @ 1% Methane
|
General purpose catalytic pellistor
sensor for use in Fixed Gas Detection Systems. Poison
resistant. Supplied as matched pairs, mounted on twin TO4
size headers. |
 |
|
NP-30SH |
2V |
300mA |
40mV @ 1% Methane
|
As NP-30, but lower cost device,
mounted in a single header enclosure. |
|
|
NP-17 |
2V
|
175mA
|
20mV @ 1% Methane
|
General purpose catalytic pellistor
sensor for use in Fixed Gas Detection Systems. Poison
resistant. Supplied as matched pairs, mounted on twin TO4
size headers. |
|
|
NP-17SM |
2V
|
175mA
|
20mV @ 1% Methane
|
As NP-17, but lower cost device,
mounted in a single header miniature enclosure. |
|
|
NP-17SL |
2V
|
175mA
|
20mV @ 1% Methane
|
As NP-17, but lower cost device,
mounted in a single header miniature enclosure. |
|
|
NP-17SH |
2V
|
175mA
|
20mV @ 1% Methane
|
As NP-17, but lower cost device,
mounted in a single header miniature enclosure. Suitable for high
temperature applications up to 180 deg C |
|
|
NP-18 |
2.6V
|
170mA
|
20mV @ 1% Methane
|
General purpose catalytic pellistor
sensor for use in Fixed Gas Detection Systems. Poison
resistant. Supplied as matched pairs, mounted on twin TO4
size headers. |
|
|
NP-18SM |
2.6V |
170mA |
60mV @ 1% Methane |
As NP-18, but lower cost device,
mounted in a single header enclosure. |
|
|
NP-ANSM |
2.2V |
160mA |
23mV @ 1% Ammonia |
Special Purpose catalytic pellistor sensor designed to
monitor low LEL levels of Ammonia. As NP-AN, but mounted in a lower cost, single header
enclosure |
|
|
NP-AHSM |
1.6V |
140mA |
80mV @ 1% Hydrogen |
Special Purpose catalytic pellistor sensor designed to
monitor low LEL levels of Hydrogen. As NP-AH, but mounted in a lower cost, single header
enclosure |
|
|
NP-AC |
2V |
140-165mA |
8mV@10%LEL Acetylene |
Special Purpose catalytic pellistor sensor designed to
monitor low LEL levels of Acetylene. Poison resistant. Supplied as matched pairs, mounted on
twin TO4 size headers. |
|
How do Catalytic type Gas Sensors
work?
Catalytic combustion has
been the most widely used method of detecting flammable gases in
Industry since the invention of the catalytic pelletized resistor
(or "Pellistor") in the mid 1960's.
A Pellistor consists of a
very fine coil of platinum wire, embedded within a ceramic pellet.
On the surface of the pellet is a layer of a high surface area
noble metal, which, when hot, acts as a catalyst to promote
exothermic oxidation of flammable gases. In operation, the pellet
and so the catalyst layer is heated by passing a current through
the underlying coil. In the presence of a flammable gas or
vapour, the hot catalyst allows oxidation to occur in a similar
chemical reaction to combustion. Just as in combustion, the
reaction releases heat, which causes the temperature of the
catalyst together with it's underlying pellet and coil to rise.
This rise in temperature results in a change in the electrical
resistance of the coil, and it is this change in electrical
resistance which constitutes the signal from the sensor.
Pellistors are always
manufactured in pairs, the active catalysed element being
supplied with an electrically matched element which contains no
catalyst and is treated to ensure no flammable gas will oxidise
on it's surface. This "compensator" element is used as
a reference resistance to which the sensor's signal is compared,
to remove the effects of environmental factors other than the
presence of a flammable gas.
Pellistor
Drive/Measurement Circuit: A simple Wheatstone Bridge
to compare the resistance of two hot elements
The advantage of using this
technique when detecting flammable gases for safety purposes is
that it measures flammability directly.
Nemoto provides matched
pair Pellistors conveniently mounted in TO4 size headers, or as
complete flameproof Gas Detection Heads for use as field devices
within fixed Gas Detection Systems.
|
