E-mail: michael@shboqu.com   |   Expert in Water Quality Measurement and Water Treatment Project

How to deal with failures in the daily maintenance of COD analysis instruments?

by:BOQU     2021-08-11

Daily protection of online cod measurement is very important, check at least once a week. Including the working conditions of reagents, pipes, and samplers. Especially the aging of the waste liquid discharge pipe (drain valve) hose must be replaced in time (January). The measuring cuvette should also be cleaned punctually, paying attention to the upper and lower sealing gaskets.

1. The first question about the sampler

First check whether the sampling pipe is blocked or not, whether the sampler is working properly, and then check the condition of the sampling submersible pump (whether the pipeline is leaking; piston pump).

2. Reagent problem

First enter the service menu, open the safety panel and check the corresponding reagent bottle to determine that the XX reagent is used up, and the reagent must be added in time. But if so, you need to check whether the reagent bottle is too full, and whether the reagent bottle cap is screwed too tightly. If it is too tight, the reagent will not suck in without air.

3. The damage of sulfuric acid valve and potassium cadmium valve is also often present, but the sulfuric acid valve is the most harmful

COD max alarm has no sulfuric acid reagent. If the sulfuric acid in the reagent bottle is eliminated, the pipeline is not blocked, the other valves are normal, and the syringe is normal. If the function test is still unable to absorb the sulfuric acid, it can be determined that the sulfuric acid valve is damaged. It can also be removed for careful inspection and judgment. Generally, the diaphragm in the sulfuric acid valve is corroded and deformed by sulfuric acid for a long time.

4. The problem with the syringe

After ruling out that the sampler is normal, the valves are normal, there are reagents, and the tubing is not blocked, but the sample still cannot be sucked up. You can remove the syringe to check. It can be tested manually. One hand blocks the lower mouth of the syringe and the other hand pulls the plunger rod of the syringe. If it is easily pulled out, it can be judged that the syringe is leaking and needs to be replaced. You can also remove the syringe and suck some tap water. If the water drops naturally, it can be judged that the piston of the syringe is leaking.

5 The problem with the drain valve

It is determined that the sampler is normal, the reagent valve is normal, the injection valve is normal, and the syringe is normal. However, if the liquid still cannot be pumped, it can be judged that there is a problem with the discharge valve (the injection valve generally does not corrode). By observing whether there are traces of corrosion and whether the black powder is dropped, it can be determined whether the caliper of the drain valve is damaged or not.

6. The problem of measuring test tubes

Observe whether the inner wall of the measuring test tube has swelling and dirt, and then you can judge whether the measuring test tube should be cleaned or not.

7. The problem of LED measuring the bump signal of the test tube

However, the inner wall of the measuring test tube is clean, you need to check the high and low signal values u200bu200bin the signal menu. Normally, both should be above 2000. If the signal is below 600, it is a corresponding LED problem. After adjusting the photometer, the signal value still cannot go up. It can be determined that there is a problem with this LED and the photometer needs to be replaced. If it is still impossible to replace the photometer, it must be a problem with the detection signal components.

8. CODmax alarm amplifier positioning

It may be that the communication of the control unit circuit board has moved out. It can be handled like this, enter the control unit menu of the service menu (press the F2 key for more than 2 seconds), and check whether the piercing items are all ready. If the name of the board appears, it means that it does not communicate. You can use the piercing item, use a magnetic screwdriver to click the magnetic strip of the corresponding circuit board, and it will appear after the name of the corresponding circuit board * At this time, select F2 (virus) to pierce.

But if the circuit board is broken (the magnetic stripe does not respond), the communication bus is normal, and the circuit board needs to be replaced. Some instruments often display alarms from the control unit, sometimes resetting or piercing is just fine, and it happens repeatedly. You can upgrade the COD max program, that is, upgrade the 1.24 version to 1.25.

9. Amplifier positioning alarm

First, the bump signal value of the measuring test tube is too low.

There is also the formation of the clogged discharge pipe and failure to open the digestion inlet valve. Pay attention to the following two points when disassembling and cleaning the digestion inlet valve. Be careful not to damage the connecting rod between the valve and the digestion tube. When disassembling the motor, turn it counterclockwise to unscrew it, and do not pull it out forcefully.

10. Sometimes the measurement value is suddenly low in the measurement

Some changes to 0 may be due to the following reasons:

Reagents were not proofread in time after replacement, so they must be proofread immediately after replacement.

The COD value of water samples is inherently low, such as below 20 or even below 10. Our instrument is suitable for measuring wastewater with the COD value of 10-5000mg/L, and it can perform normal measurement conditions in this range. However, if the instrument measures a lower COD value for a long time, the instrument will gradually drift downward, causing it to become a negative value. The processing method can be calibrated with the 2050120 standard solutions. In addition, the chloride ion content in the water sample is too high to exceed 5g/L, which can also cause the measured value to be low.

11. Sometimes the measured value in the measurement is too high (refers to the instrument that usually measures in the low range)

One is that it is suddenly high once or several times. It may be that the drain sample is unstable and the instrument has no problem.

Second, if it is always high and above 1000, it may be that the foreign matter is attached to the wall of the digestion tube when the water sample is taken, and it will be normal after cleaning. There are also some reagents prepared by customers themselves, and the deposition of potassium dichromate can also cause the measurement value to be high. Use active cleaning to clean the pipeline and test tube with hot sulfuric acid first, and then use the standard solution to calibrate.

12. The temperature alarm of the digestion test tube is greater than 200 degrees

When there is no line fault, the digestion test tube is usually broken and needs to be replaced immediately.

13. Humidity alarm

That is, the internal pipeline of the instrument may be blocked, damaged, or the inlet valve may leak at night to cause a humidity sensor alarm. The clean tray can be arranged with gauze and can be processed after drying.

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