4

ZAF-3

MEASURING PRINCIPLE

Fixed resistor

DC amplifier

Sample gas

DC

constant

current

Measuring

chamber

Reference

chamber

This thermal conductivity gas analyzer measures gas con-

centration by utilizing the different thermal conductivities

of 2 gas components. In the detector, there are reference

and measuring chambers in each of which a thin platinum

wire is stretched. The reference chamber is filled with ref-

erence gas and through the measuring chamber, sample

gas is flowed. Each platinum wire composes a bridge cir-

cuit in combination with an external fixed resistor, and it is

heated by flowing a constant current. When there is a change

in the concentration of the component under measurement,

the thermal conductivity of sample gas will change to af-

fect the temperature of the platinum wire in the measuring

chamber. The resulting thermal change is taken out as a

change in electric resistance, according to which the con-

centration of measured gas is calculated.

Thermal Conductivity Ratio of Gases

Measured gas

Reference gas

component (Note 1)

He

Ar

Measurable range

Range

ratio(Note 2)

1 : 10

Air

1 : 5

1 : 10

1 : 5

100 to 80%

1 : 5

(Note 2) Range ratio stands for maximum value.

Gases

Comparative thermal conductivity

(0

°C) when replacing thermal

conductivity of air

(2.41 x 10

Sulfur dioxide gas

Carbon dioxide gas

Argon

Ar

Carbon monoxide

CO

Steam (100

°C)

Air

Nitrogen

Oxygen

Methane

Hydrogen

Peltier gas

cooler

(Note 2)

(Note 2)

Sample

gas

(Note 1)

Gas

aspirator

Flow

checker

0.4L/min

or 1L/min

(Note 3)

1L/min

Membrane

filter

Mist

filter

Mist

filter

Exhaust

Purging

air or

nitrogen

Drain pot

ZAF

(Note 1) Dust must be purged adequately

(for protection of the pump, flowmeter, etc.).

(Note 2) Unnecessary if sample gas is dry.

(Note 3) Select the one with no pulsating flow within the specified

flow rate range.

Solenoid valve

Pressure reducing valve

Span

gas

Zero

gas

Span calibration signal

Suction pump OFF signal in automatic calibration

Zero calibration signal

Example of gas measurement in industrial furnace, sintering furnace, etc.

Table 1: Measurable Component and Measurable Range

GAS SAMPLING SYSTEM DIAGRAM (EXAMPLE)