Paramagnetic method

Method 1 Paramagnetic method : magneto-pneumatic type

The paramagnetic method is a measuring principle that utilizes the extremely strong paramagnetism (*1) of oxygen. When oxygen is present in an inhomogeneous magnetic field, it is attracted to the stronger magnetic field. The magneto-pneumatic type of the oxygen analyzer uses this property to detect the amount of oxygen attracted as pressure. This analyzer uses electromagnets as the magnetic force and is divided into single and double measurement methods based on the number of sets of electromagnets in the magnetic field cell. A condenser microphone detector (*2) is used for a pressure detection in both methods.

(*1) Paramagnetism: A material that is not magnetized in the absence of a magnetic field but is magnetized in the direction of the magnetic field when a magnetic field is present.

(*2) Condenser microphone detector: This detector uses a condenser microphone as a sensor. A condenser microphone consists of a diaphragm and a fixing plate. When a pressure differential occurs between the left and right sides of the diaphragm, the distance between the diaphragm and the fixing plate changes. This distance change is taken as the capacitance change of the condenser, and the pressure difference is detected.

Method 1-1: Paramagnetic method magneto-pneumatic type (single magnetic field)

Features

Since the sample gas does not directly contact the detector, it is highly resistant to corrosion and other deterioration, ensuring stable long-term operation and maintenance-free operation.
Oxygen concentration can be measured with higher sensitivity even when flammable gases exist in the sample gas.

Measuring principle

The measuring principle utilizes the extremely strong paramagnetism of oxygen. When oxygen (a paramagnetism gas) is present in a magnetic field, it is attracted to the stronger magnetic field and increases the pressure in that area increases. In general, the pressure increase (ΔP) at that time can be expressed by the following equation

ΔP = 1/2 H₂・X・C
(H : strength of magnetic field X : magnetic susceptibility of a paramagnetism gas (oxygen) C : difference concentration between a paramagnetism gas (oxygen) and a carrier gas(air/nitrogen))

This pressure increase is detected and the oxygen concentration is measured.

Structure and operating principle (Figure 1-1)

The pressure change caused by oxygen in the sample gas at the electromagnet ON/OFF is propagated to the condenser microphone detector outside the magnetic field cell by a carrier gas, and the oxygen concentration is measured by the detected pressure change corresponding to the oxygen concentration.
The pressure propagation to the detector by the clean carrier gas ensures long-term stable measurements because corrosive gases in the sample gas and contaminants in the magnetic field cell do not come into contact with the detector. In addition, when using the atmosphere as a carrier gas, an N₂ cylinder is not required.

Figure 1-1: Structure and operating principle of a paramagnetic method magneto-pneumatic type (single magnetic field) of an oxygen analyzer

Method 1-1: Paramagnetic method magneto-pneumatic type (double magnetic field)

Features

In addition to the features of a single magnetic field, two sets of electromagnets are alternately switched ON/OFF to achieve even higher sensitivity measurement than a single magnetic field.

Measuing principle

It is the same as a single magnetic field.

Structure and operating principle (Figure 1-2)

In addition to the single field operation, when one electromagnet is ON, the other is OFF, and this is repeated alternately.
This operation switches the direction of the pressure applied to the condenser microphone in the detector, providing twice the amount of signal to be detected compared to a single magnetic field. By detecting twice the amount of signal, a more sensitive measurement result can be obtained compared to a single magnetic field.