JPS5815062B2 - How to calibrate a magnetic oxygen analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for calibrating a magnetic oxygen analyzer.

In particular, the present invention is a method for performing span calibration of a high-sensitivity magnetic oxygen analyzer that measures oxygen concentration in a range of 1% or 2% using an air standard (i.e., based on the oxygen concentration in the air). It's about technology.

Generally speaking, there are two methods for measuring oxygen concentration that are generally employed in this type of magnetic oxygen analyzer.

One of these is oxygen concentration measurement using the zero reference method, and the other is oxygen concentration measurement using the air reference method.

The former measures zero meter fluctuation when the oxygen concentration in the measurement gas is 0%, and measures the oxygen concentration up to a certain range, and usually uses 100% nitrogen gas, which is a highly magnetic gas, as the auxiliary gas. It will be done.

The latter assumes that the meter swing is zero when the oxygen concentration in the measurement gas is equal to the oxygen concentration in the air (strictly speaking, 20.96%, hereinafter roughly referred to as 21%), and uses this as a reference to measure the measurement gas in the measurement gas. The oxygen concentration in the air is measured, and dry air is normally used as the auxiliary gas.

In addition, magnetic oxygen analyzers are highly sensitive and can measure within a range of 1% or 2%, but when performing zero point calibration and span calibration for these oxygen analyzers,
In the former zero reference type oxygen analyzer, 0 is used instead of the measurement gas.
% and other predetermined oxygen concentrations can be easily calibrated by flowing a standard gas.

On the other hand, 21 included in the latter air-based oxygen analyzer
High-sensitivity oxygen analyzers in the ~20% and 21-19% ranges cannot be calibrated with high precision using simple operations as described above.

Since this air-based oxygen analyzer uses normal atmospheric air, that is, dry air with an oxygen concentration of 21%, as the auxiliary gas, its zero point calibration is performed by flowing the same dry air as the zero gas into the measurement chamber until the meter pointer swings to zero. This is possible by checking whether or not.

However, when span calibration is performed by flowing a standard gas with an oxygen concentration of around 21% into the measurement chamber as a span gas, the meter pointer deflection is ±40% for an oxygen analyzer in the 1% range, and 2% for an oxygen analyzer in the 1% range.
Microwave oxygen analyzers have an error of ±20%.

The reason for this is due to the following circumstances.

Generally, the concentration of standard gas has an error of ±2% with respect to the displayed value.

By the way, the concentration and error concentration of typical gases are shown in the table below.

As will become clear from this, standard gas of around 21% has ±
Since it contains an absolute error of 0.4%O2, this is reduced to 1
When supplied as a span gas to a high-sensitivity oxygen analyzer in the % range or 2% range, a measurement error of 40% or 20% occurs, respectively.

The occurrence of such a large error during the span calibration of an oxygen analyzer is not desirable for an oxygen analyzer, and some kind of solution has been requested.

The present invention is intended to solve such problems,
The purpose is to improve the accuracy of span calibration of air-based high-sensitivity oxygen analyzers by providing a new calibration method.

In order to achieve this objective, in the present invention, 21 to 20%,
A range change switch is installed on an oxygen analyzer with any range width such as 21 to 19% range, and when performing span calibration, the oxygen analyzer can be set to 21 to 0% range by changing the range.
After converting to a microwave oxygen analyzer and performing span calibration on the oxygen analyzer after conversion using N2 pure gas, switch the range again to increase the gain of the amplifier to 20 times or 10.5 times so that it can be used again. ing.

The present invention will be described in detail below regarding an oxygen analyzer in the 21-20% range.

FIG. 1 schematically shows the structure of a magnetic oxygen analyzer to which the method of the present invention is applied.

The device has a measuring chamber 1 which communicates with an inlet 2 and an outlet 3 for the inflow of measuring gas.

On the other hand, an auxiliary gas conduit 4 for supplying auxiliary gas to the measurement chamber 1 is provided.

This auxiliary gas conduit 4 becomes two branch pipes 5, 5' capable of equally dividing the auxiliary gas flowing through the conduit, and communicates with the measuring chamber 1 at conduit outlets 6, 6', respectively.

An electromagnetic device 8 is provided near one of the conduit outlets 6'.

Further, the branched conduits 5 and 5' are further branched into a route different from the route toward the conduit outlet, forming a connecting pipe 7 that communicates with each other, and a bridge circuit is constructed inside the intermediate position of the connecting pipe 7. A flow detector having a hot wire flow detection element 9 is arranged.

Now, a measurement gas containing oxygen is flowed into the measurement chamber 1 from the inlet 2, and auxiliary gas is supplied from the auxiliary gas conduit 4, and the electromagnet device 8 is activated.

Then, a magnetic field is generated near the conduit outlet 6', and at this outlet, an interfacial pressure corresponding to the oxygen concentration in the measurement gas is generated between the measurement gas and the auxiliary gas, which attempts to prevent the introduction of the auxiliary gas. do.

On the other hand, the auxiliary gas flowing through the conduit outlet 6 is not subject to any restrictions.

Therefore, a flow of auxiliary gas occurs in the coupling conduit 7, so that
This flow is detected by the hot wire flow rate detection element 9, and the oxygen concentration in the measurement gas can be measured.

When performing zero point calibration and span calibration in this oxygen analyzer, the same operation as above is performed by injecting zero gas or span gas from the inlet 2, and the degree of meter deflection is checked.

In order to perform these zero point calibration and span calibration, in this example, the oxygen analyzer was prepared in advance so that it could switch between two ranges: 21-20% and 21-0%, and a measurement system as shown in Figure 2 was installed. Configure.

In FIG. 2, a group of measurement gases or standard gases are surrounded by a dotted line A, and after being filtered by a filter 10, they flow into the measurement chamber 1 through an inlet 2.

Further, the dry air indicated by arrow B indicates the auxiliary gas flowing into the measurement chamber 1 through the auxiliary gas conduit 4.

After configuring the measurement system as described above, first, to calibrate the zero point of the oxygen analyzer in the 21 to 20% range mentioned in this example, use dry air, that is, air in the atmosphere, as an auxiliary gas. The valves 11, 12, and 13 are operated so that the same dry air flows into the measuring chamber 1 from the inlet 2 as zero waste.

If this oxygen analyzer is operated in this manner, the deflection of the meter pointer becomes zero, and zero point calibration can be performed.

Next, to perform span calibration of this oxygen analyzer, first change the range between 21 and 20%.
It is converted into an oxygen analyzer with a range of 1 to 0%, and valves 11 and 1 are installed so that pure N2 gas flows into the measurement chamber 1 as a span gas.
Operate 2 and 13.

In this manner, span calibration can be performed by operating the converted oxygen analyzer and adjusting the deflection of the meter pointer.

In this way, after zero point calibration and span calibration are completed, in order to measure the oxygen concentration of the measurement gas whose oxygen concentration is 21 to 20%, the oxygen analyzer, which had been in the 21 to 0% range, was changed to 21 to 20%. Range width 1% by switching to range
It can be enlarged and measured.

In this way, when span calibration is performed, N
2. Because pure gas was used, even if the amplifier gain was increased by 21 times by switching the range, the span calibration accuracy could be kept at ±4.
%.

In addition, in the case of an oxygen analyzer with a range of 21 to 19%, convert it to an oxygen analyzer with a range of 21 to 0% when calibrating the span.
After performing span calibration, by switching to the original 21-19% range, highly accurate measurements can be made within a range width of 2%.

At this time, the amplifier gain becomes 10.5 times, and the span calibration accuracy becomes ±2%.

In order to employ the method of calibrating an oxygen analyzer as described above, it is sufficient to equip the oxygen analyzer with dry air for zero gas and pure N2 gas for span gas.

This allows zero point calibration and span calibration to be performed periodically.The reason why such simple calibration can be performed by switching ranges is that the magnetic oxygen analyzer itself has good linearity, and the amplifier gain between ranges is This is because the characteristics of the amplifier hardly change over time.

If the oxygen analyzer itself has poor linearity, adjust the span between ranges using the following procedure.

That is, as mentioned above, convert the 21 to 20% range oxygen analyzer into a 21 to 20% range oxygen analyzer by changing the range, perform span calibration using N2 pure gas, and then convert the oxygen analyzer to 21 to 20% range oxygen analyzer by changing the range. The concentration of the standard gas can be calibrated by supplying a standard gas with an oxygen concentration of around 20% from the inlet 2 to the measurement chamber 1 while leaving the range at 0%.

At this time, the output reproducibility of the oxygen analyzer itself in the 21-0% range is ±0.2%, so when converted to oxygen concentration, 0.21X0.002=0.00042 (=±0.042 % oxygen concentration) In other words, the standard gas with an oxygen concentration of around 20% is ±0.04
This means that calibration can be performed with an error of 2% concentration.

If this error is expressed as a percentage, it will be as follows.This means that the standard gas with an oxygen concentration of around 20% was calibrated with an accuracy of ±0.2%.

Therefore, if you switch the oxygen analyzer that used to be in the 21 to 0% range to the 21 to 20% range and perform span calibration in this range, the 1% range width will be 21 times the amplifier as compared to the 21% range width. Gain and span calibration accuracy is ±
It becomes 4%.

In this way, span calibration between ranges is performed and instrument adjustment is completed.

5. Even if the amplifier gain between ranges changes over time over a long period of time, the span between ranges can be adjusted by the same operation as described above.

For this purpose, in the system shown in Figure 2, the oxygen concentration 2
It is preferable to have an extra standard gas of around 0% (20% 02+N2).

As explained above, according to the present invention, when performing span calibration on a high-sensitivity air-based oxygen analyzer, the oxygen analyzer is first set to a range of 21 to 0% by changing the range, and then the absolute By performing span calibration using pure N2 gas, which has extremely small errors, it has become possible to calibrate oxygen analyzers with about 10 times more accuracy than a span calibration method that does not involve range switching. .

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the principle of a magnetic oxygen analyzer to which the present invention is applied. FIG. 2 shows a device configured for using the method of the present invention.
It is a system diagram incorporating a measurement gas circuit, a zero gas circuit, and a span gas circuit. Explanation of symbols: 1...Measurement chamber, 2...Inlet, 3...Exhaust port, 4...Auxiliary gas conduit, 5, 5' ...Branch conduit, 6,6'...
... Conduit outlet, 7 ... Connection pipe, 8 ...
...Electromagnetic device, 9...Hot wire flow rate detection element,
10... Filter, 11, 12, 13...
··valve.

Claims (1)

[Claims] 1 Using air as an auxiliary gas and utilizing the interfacial pressure difference 2
21 is an air-based magnetic oxygen analyzer that measures the oxygen concentration in the sample gas over a range width of 1% or less.
A magnetic oxygen analyzer characterized in that a switching range of ~0% is provided, the range is converted to 21~0% during span calibration, and span calibration is performed by supplying pure N2 gas as span gas. Calibration method.