JPS621214B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a technique for preparing a standard solution used for calibrating a measuring device in which measurement results are displayed on a ^logarithmic scale or a substantially logarithmic scale, such as an ion concentration meter that measures the concentration of Na + and the like.

BACKGROUND ART In recent years, in response to the increase in high-pressure and large-sized boilers in thermal power plants, there has been a demand for higher quality feed water supplied to the boilers, and the importance of water quality monitoring has increased. In particular, contamination of Na ⁺ causes sodium corrosion in high-temperature, high-pressure boilers, so a condensate desalination device made of a large capacity ion exchange resin is used to
The Na ⁺ concentration is controlled to an ultra-low concentration of 2.3 ppb or less, and therefore, when monitoring water quality, it is necessary to accurately measure ultra-low concentrations of Na ⁺ .

A sodium monitor using a special sodium ion electrode has been developed as a device for continuous measurement of ultra-low concentrations of Na ⁺ , and is used to measure Na ⁺ in condensate leaving a condensate desalination equipment. There is. The measurement range of this sodium monitor is Na ⁺ concentration 0.1~
100ppb, during normal measurement during boiler operation.
The Na ⁺ concentration is 0.1-1 ppb, and when the capacity of the ion exchange resin in the desalination equipment decreases, the Na ⁺ concentration increases,
When the level reaches 2.3 ppb, an alarm is issued and the ion exchange resin is regenerated.

Therefore, in sodium monitors, especially
Accuracy around 2.3 ppb is required. In order to meet this level of accuracy, it is most preferable to calibrate with two trace sodium standard solutions containing 2.3 ppb, but the concentration of sodium standard solutions that can be prepared in the field is at most 50 ppb, and lower than that. It is actually extremely difficult to prepare a concentration standard solution. Even if it were possible to prepare a trace amount of sodium standard solution with an ultra-low concentration as described above, the atmosphere point of the sodium electrode would have a Na ⁺ concentration.
It is at a position of 2.3%, which is an alarm point.
Since the Na ⁺ concentration of 2.3 ppb is separated by 10 ^-7 , when calibrating with two trace sodium standard solutions, a so-called seesaw occurs when adjusting the atmosphere point and span, making the calibration work extremely difficult.

For this reason, sodium monitors are generally calibrated as follows.

In other words, it has been experimentally confirmed that the special sodium electrode used in sodium monitors can obtain the theoretical value output up to a Na ⁺ concentration of 0.5 ppb. Input the value signal and adjust it to the theoretical value. On the other hand, regarding the atmospheric point, 50ppb was prepared by dissolving sodium chloride (NaCl) in high-purity water.
Alternatively, a 100 ppb standard solution is poured into the device, and when the readings become stable, calibration is performed using the atmosphere volume to match the concentration of the standard solution.

However, even with this calibration method, it is necessary to ensure a flow rate of about 300 ml/min, and a large amount of standard solution is required for one calibration. Although it is possible to prepare large quantities of standard solutions of 50 ppb to 100 ppb, it is quite troublesome, especially
When examining reproducibility, a larger amount of standard solution must be prepared, which is inconvenient for transportation.

In view of the current situation, the present invention provides a standard solution preparation method and device that are effective for simplifying calibration work and can continuously prepare a standard solution of a desired concentration using sample water that can be obtained at any flow rate on site. This is what we propose.

Examples of the present invention will be described based on the drawings.
Figure 1 shows a standard solution preparation device, A is a detector of a measuring device such as an ion concentration meter where measurement results are displayed on a logarithmic scale, and 1 is a piping system that supplies a constant flow rate of sample water to the detector A. and overflow tank 1
a, it has a throttle valve 1b. Reference numeral 2 denotes a standard solution preparation piping system having a high concentration standard solution storage tank 2a, a metering pump 2b, and an on-off valve 2c, and is connected to the middle of the former piping system 1.

According to the above device, when measuring sample water, the sample water entering from the sample inlet is transferred to the overflow tank 1a.
The pressure is regulated to a constant head by the throttle valve 1b, the flow rate is restricted to a constant value by the throttle valve 1b, and the sample water is introduced into the detector A, where the sample water is measured.

During calibration, when the on-off valve 2c is opened with a constant flow rate of sample water and the metering pump 2b is operated in the same manner as in sample water measurement, a fixed amount of the high concentration standard solution in the storage tank 2a is added to the sample water. injected into
They are mixed in the piping system 1 to become a standard solution with a predetermined concentration and are continuously supplied to the detector A.

For example, when preparing the sodium standard solution for the sodium monitor calibration mentioned above, while flowing the water (sample water) from the outlet of the desalination equipment into the piping system 1,
A high concentration sodium standard solution prepared in advance is flowed into the piping system 2, and both are mixed within the piping system 1 to continuously prepare a sodium standard solution of a desired concentration.

Now, the flow rate of sample water that does not contain Na ⁺ is 300ml/min.
High concentration sodium standard solution stored in storage tank 2a
Na ⁺ concentration is 100ppm, metering pump 2b capacity is 0.3
ml/min, the Na ⁺ concentration of the sodium standard solution that is continuously prepared by mixing the two is
It becomes 100ppb.

However, in reality, the presence or absence of Na ⁺ in the sample water,
The concentration is unknown, and the standard solution is prepared by diluting the high concentration standard solution with this sample water, so if the sample water contains Na ⁺ , the Na ⁺ concentration of the sample water will be adjusted. This will appear as an error in the standard solution.

In this case, the sample water is the water at the outlet of the condensate desalination device, and the Na ⁺ concentration of this sample water is typically between 0.1 and 2.3 ppb, as mentioned above.

Therefore, when the Na ⁺ concentration of the water (sample water) at the outlet of the desalination equipment changes, the standard solution Na ⁺
The concentration is calculated as follows.

Na ⁺ concentration of sample water Na ⁺ concentration of standard solution 0.1ppb 100.1ppb 1ppb 101ppb 2.3ppb 102.3ppb 10ppb 110ppb If each of the above standard solution concentrations is regarded as a 100ppb standard solution and the sodium monitor is calibrated using the method described at the beginning, Sodium monitor is Na ⁺
Since the concentration measurement result is displayed on a logarithmic scale, and the standard solution concentration is one order of magnitude higher than the sample water concentration, the error is very small and can be ignored.

In other words, since it is a logarithmic scale, the scale width is wide in the range of 0.1 to 2.3 ppb, which is the normal measurement range of sodium monitors, but the scale width is wide in the range of 100.1 to 102.3 ppb, which is the actual concentration of the standard solution. The width is very narrow, 100.1 to 102.3 ppb
Even if calibration is performed assuming that the value is 100 ppb, the error caused by this is extremely small and can be ignored.

By the way, the standard solution with Na ⁺ concentration 102.3 ppb is 100 ppb.
When calibrated using the standard solution, when the scale indicates the alarm point of 2.3 ppb, the true value is 2.35 ppb, which is a negligible error.

It is unlikely that the condensate Na ⁺ concentration exceeds 2.3ppb, but even if it is extremely higher than the alarm point of 2.3ppb
Even if it is assumed that the concentration is 10ppb, if the standard solution of 110ppb prepared using 10ppb condensate is calibrated as 100ppb, the true value when the alarm point of 2.3ppb is indicated is 2.53. It is ppb. This degree of error does not pose a practical problem when considering the accuracy of the apparatus.

Furthermore, Na ⁺ is present in large amounts in the atmosphere and is likely to be mixed in during the preparation of the standard solution; therefore, the higher the concentration of the standard solution is, the less the influence of the contamination will be, which is advantageous. In this regard, the high concentration standard solution prepared in advance is
Since the concentration is as high as 100 ppm, the influence of Na ⁺ contamination in the atmosphere is small, and this high concentration standard solution and sample water can be mixed in piping system 1.
In other words, we prepare standard solutions in ppb units.
Since the standard solution is prepared under sealed conditions, there is almost no influence from contamination of Na ⁺ in the atmosphere, even though the standard solution prepared has a low concentration on the ppb level.

It is also possible to configure the throttle valve 1b and the opening/closing valve 2c to be configured to perform automatic calibration by using electromagnetic valves and combining them with a control circuit such as a timer. The means for adjusting the sample water to a constant flow rate is not limited to the overflow method shown in Fig. 1, but also the pressure regulating valve 1 as shown in Fig. 2.
The flow rate may be adjusted to a constant value by a combination of the flowmeter c, the throttle valve 1d, and the flowmeter 1e.

Furthermore, the method of adding the high concentration standard solution is not limited to the metering pump method shown in Fig. 1, but for example, as shown in Fig. 3, the high concentration standard solution tank may be set at a constant head and the flow rate may be adjusted to a constant flow rate using the orifice 2f. It may also be added to the sample water.

As described above, in a measuring device in which measurement results are displayed on a logarithmic scale, if calibration is performed using a standard solution with a concentration one or more orders of magnitude higher than the measurement range, the concentration of the sample water will change to some extent. Focusing on the fact that even if there is variation, the error between the indicated value and the true value in the measurement range is extremely small and can be ignored, we developed sample water that can be easily collected in any amount at the measurement site, and that is suitable for on-site work. Highly concentrated standard solutions, which can be produced easily and accurately, are mixed at a constant flow rate within a piping system to continuously produce a standard solution of a desired concentration.

Therefore, even if the standard solution has a low concentration in ppb units,
It can be easily and accurately prepared by on-site work, eliminates the inconvenience of transporting and storing large amounts of low-concentration standard solutions in containers, and facilitates calibration of measuring equipment. It is extremely effective in simplifying work.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, Fig. 1 is a piping diagram of a standard solution preparation device, Fig. 2 is a piping diagram of main parts showing another embodiment, and Fig. 3 is a piping diagram showing still another embodiment. It is. 1... Piping system, 2... Piping system, 2a... High concentration standard solution storage tank.

Claims (1)

[Claims] 1. A method for preparing a standard solution used for calibrating a measuring device in which measurement results are displayed on a logarithmic scale or a substantially logarithmic scale, the method comprising: adding a high concentration standard solution to a constant flow rate of sample water; A standard solution preparation method characterized by continuously preparing a standard solution by injecting the same. 2 A device for preparing a standard solution used for calibrating a measuring device whose measurement results are displayed on a logarithmic scale or a nearly logarithmic scale, which includes a piping system that supplies a constant flow of sample water to the detector of the measuring device and a high concentration standard. A standard solution preparation device comprising a piping system that injects a constant flow rate of a highly concentrated standard solution taken out from a liquid storage tank into sample water midway through the piping system.