Conductivity meter replacement and calibration

Conductivity represents the conductivity of various ions in aqueous solution. It can be used to represent the total amount of various ions. It is accurate, simplifies the detection method, and can measure on-line, monitoring the working condition of the wastewater treatment system at any time. The newly-installed on-line conductivity meter has a new host and conductivity cell. After installation and debugging at the factory site, the accuracy is relatively reliable. However, when the on-line conductivity meter has been in operation for a long time, especially when the conductivity cell is immersed in the treated wastewater for a long time, it tends to age. In this way, for some reason, some of the treated water that cannot meet the discharge standard can be due to the reaction of the conductivity cell. Oblivious, misunderstood that it can be discharged, and it will be passed. How many tons of waste water that will not reach the standard will be injected into the Minjiang River each year? Nominally there are instruments that monitor the discharge of waste water. Actually, they are in fact useless. There is nothing worse than nothing. Today, when it comes to advocating environmental protection, it is particularly important to calibrate the on-line conductivity meter.

The solutions to these three problems are described separately below:

(1) At the beginning of this work, it was found that most of the electrodes were already aging, and the measured data was basically unreliable. It is recommended that the manufacturers change their batteries.

(2) Solve the problem of excessively large probe cell volume: Remove the probe from the sewage ditch and put it into the bucket to clean it. Carefully remove the probe cover to restore the size of the conductivity cell of the conductivity meter.

(3)Solution of the problem of the dirty cell probe: Use the cotton to gently wipe the probe in the reduced conductivity cell, flush it with distilled water, and dry the test paper.

(4) Solve the problem of measuring range:

Because only the standard solution of 147.7μs/cm (25°C) was purchased from the national standard center, it is only possible to measure the on-line conductivity meter of this range from 0 to 200.00μs/cm, and it cannot measure the range of 0 to 20.00μs/cm. Online conductivity meter, what should I do? Let the customer buy a new 0.2-grade portable conductivity meter and measure the host to 0.2 with the conductivity meter tester, that is, the electricity meter reaches 0.2, and then measure the conductivity cell with the conductivity standard solution. Machine matching error, see if it also reached 0.2. When both items reach level 0.2, they are ready for use. Use this newly purchased conductivity meter to match the standard solution in the 0 to 20.00 μs/cm range to solve the span problem.

It is much more convenient to calibrate after being prepared. Place the conductivity cell directly into the standard solution, place different standard solutions in different ranges, read the data, and see a bit of error. Find the CHECK point. Use a screwdriver to adjust the number and standard of the panel. The standard value of the solution is basically the same, fast and accurate, and won praise from users.

First, the conductivity meter verification procedures for the conductivity meter requirements

From the verification procedures, it can be seen that the on-line conductivity meter only needs to detect the instrument reference error. The conductivity of the conductivity standard solution measured by an on-line conductivity meter conductivity cell should not exceed ±4.5% FS. Otherwise, the on-line conductivity meter must be adjusted to meet the measurement requirements.

Second, the calibration of the on-line conductivity meter

First, a brief introduction of industrial conductivity meter products. The conductivity monitor can continuously measure and monitor the conductivity value of purified water and general aqueous solution for a long period of time and is suitable for on-line conductivity monitoring in the general industry.

Second, the Conductivity Meter Verification Requirements for Conductivity Meters. From the verification procedures, it can be seen that the on-line conductivity meter only needs to detect the instrument reference error. The conductivity of the conductivity standard solution measured by an on-line conductivity meter conductivity cell, the instrument reference error should not be greater than ± 4.5% FS, otherwise the on-line conductivity should be adjusted to meet the measurement requirements.

Third, the calibration of the on-line conductivity meter to be discharged. Through investigation and research, we found the following problems:

(1) Electrode aging;

(2) Oversized probe cell volume;

(3) The conductivity cell probe is too dirty;

(4) Question of range.

1. According to the formula J=K/G, the electrode constant J can be obtained by measuring the conductance G of the conductivity electrode in a certain concentration of KCl solution, at which time the K conductivity of the KCl solution is known. When measuring, the conductivity meter constant knob should be rotated to 1.0cm-1.

Because the concentration and temperature of the measuring solution are different, and the precision and frequency of the measuring instrument are not the same, the constant J of the conductivity electrode sometimes has a large error. After a certain period of time, the electrode constant may also change. Therefore, the newly purchased conductivity electrode, as well as the conductivity electrode after a period of use, the electrode constant should be re-calibrated. When measuring conductivity constants, note the following points:

(1) The conductivity meter used for the measurement should be used. Do not use other types of conductivity meter.

(2) The temperature of the KCl solution for measuring the electrode constant is preferably close to the temperature of the actually measured solution.

(3) The concentration of the KCl solution for measuring the electrode constant is preferably close to the concentration of the actually measured solution.

2. Why is the conductivity electrode plated with uranium black? Can the platinum black electrode be used to test low-conductivity solutions?

The sensitive material used for the conductivity electrode is usually platinum. The platinum plating black is coated with a layer of black fluffy metallic platinum on the platinum surface in order to reduce the polarization effect. The porous platinum black increases the surface area of ​​the electrode, reduces current density, reduces polarization effects, and reduces capacitive interference.

Platinum black electrodes that are not plated black or plated poorly can cause large measurement errors. The platinum black electrode should not be dried in distilled water during storage. If the Pt black electrode is found to be contaminated or ineffective, it can be immersed in a 10% nitric acid or hydrochloric acid solution for two minutes, then rinsed with distilled water and measured again. The platinum black electrode can also be replated, but the platinum black electrode requires certain requirements and experience. Layer plating is good and bad has a great influence on electrode performance.

In the specifications of some conductivity electrodes or conductivity meters in China, there is a misunderstanding of the platinum black electrode. It is believed that the platinum black electrode is suitable for use in high-conductivity solutions. It is not true that platinum black electrodes measure several μS/cm or even 0.1 μS. The /cm solution is acceptable, but the platinum black electrode is more stable and accurate when tested in high conductivity solutions. Therefore, the conductivity electrode with a constant greater than 1 should use a platinum black electrode. The bright conductivity electrode without platinum plating black, because it can only be used in the solution of smaller conductivity, so the conductivity electrode with the constant less than 1 can use the bright electrode. Another advantage of the bright electrode is that the surface of the platinum sheet can be wiped, while the surface of the platinum black electrode can never be wiped and can only be washed in water.