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HJ 925-2017 English PDF

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HJ 925-2017: Technical requirement and test procedures for portable dissolved oxygen meter
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Basic data

Standard ID HJ 925-2017 (HJ925-2017)
Description (Translated English) Technical requirement and test procedures for portable dissolved oxygen meter
Sector / Industry Environmental Protection Industry Standard
Classification of Chinese Standard Z16
Word Count Estimation 15,123
Date of Issue 2017-12-28
Date of Implementation 2018-04-01
Regulation (derived from) Ministry of Environmental Protection Bulletin 2017 No. 85
Issuing agency(ies) Ministry of Ecology and Environment

HJ 925-2017: Technical requirement and test procedures for portable dissolved oxygen meter

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People's Republic of China national environmental protection standards Technical requirement and test procedures for portable dissolved oxygen meter 2017-12-28 Published 2018-04-01 implementation Directory Foreword .ii 1 Scope 1 2 Normative references 1

3 Terms and definitions

4 method principle and measurement range .2 5 instrument structure 2 6 Technical Requirements 3 7 performance indicators and testing methods .4 8 Matters needing attention 7 Appendix A (Informative) Oxygen water solubility and temperature relationship .9

Foreword

In order to implement the "Law of the People's Republic of China on Environmental Protection" and the "Law of the People's Republic of China on Prevention and Control of Water Pollution", protect the environment, Protection of human health, standardization of portable dissolved oxygen analyzer technical requirements, the development of this standard. This standard specifies the technical requirements for portable dissolved oxygen analyzer, performance indicators and testing methods. Appendix A of this standard is an informative annex. This standard is released for the first time. This standard by the Environmental Protection Department of Environmental Monitoring Division and Science and Technology Standards Division to develop. This standard was drafted. Jiangsu Provincial Environmental Monitoring Center. This standard MEP approved on December 28, This standard since April 1,.2018 come into operation. This standard is interpreted by the MEP. Portable dissolved oxygen analyzer technical requirements and testing methods

1 scope of application

This standard specifies the technical requirements for portable dissolved oxygen analyzer, performance indicators and testing methods. This standard applies to portable dissolved oxygen analyzer production and testing.

2 Normative references

This standard references the following documents or the terms. For undated references, the effective version applies to this standard. GB 4208 enclosure protection (IP code) GB 7489 Determination of dissolved oxygen - iodine method GB/T 12519 analytical instruments General technical conditions HJ 506 Water quality - Determination of dissolved oxygen - Electrochemical probe method

3 Terms and definitions

The following terms and definitions apply to this standard. 3.1 Zero error Place the probe in anaerobic water to measure the difference between the oxygen measurement and the zero value. 3.2 Response time The probe from the oxygen-free water into the (20 ± 1) ℃ saturated dissolved oxygen water until dissolved oxygen analyzer showed the value rose to the theoretical value 90% of the time required. 3.3 Indication error indication error Place the probe in a constant temperature, saturated DO, and measure the difference between the DO and the theoretical value. 3.4 Repeatability repeatability Multiple measurements under the same conditions, the degree of agreement between the dissolved oxygen measurements obtained, with multiple measurements The standard deviation to represent. 3.5 Temperature indication error The probe and the standard thermometer at the same time into the water temperature measurement of water temperature, instrument measurements and standard thermometer measurements The difference between the values.

4 method principle and measurement range

4.1 Methodology 4.1.1 covered electrode method The membrane electrode method determines the amount of dissolved oxygen in water based on the diffusion rate of oxygen molecules through the selective membrane. Film electrode France dissolved oxygen detector probe with a selective membrane closed chamber, the room has two metal electrodes and full of electrolysis quality. Oxygen and a certain amount of other gases and lyophilic substances can penetrate the membrane, but water and soluble substances almost can not permeate the membrane. Film electrode method can be divided into current and polarographic two. Current-based principle is immersed in the probe when the water, due to the role of the battery potential difference between the two electrodes, so that the metal from The son enters the solution at the anode while the oxygen diffuses through the membrane at the cathode to obtain electrons to be reduced and the resulting current flows through the membrane And the electrolyte layer is proportional to the oxygen transmission rate, that is, at a certain temperature, the current and the oxygen partial pressure (or concentration) into Is proportional. The polarographic principle is that when the probe is immersed in water, the potential difference between the two electrodes is generated by the applied voltage so that the positive Extremely oxidized, while oxygen is diffused through the thin film at the cathode to obtain electrons are reduced, the resulting current flow through the thin film and the electrolyte Layer oxygen transmission rate is proportional to that at a certain temperature, the current and water partial pressure of oxygen (or concentration) is proportional to. 4.1.2 Fluorescence method Fluorescence method according to the principle of oxygen molecules on the fluorescence quenching effect to determine the dissolved oxygen content in water. Fluorescence dissolved oxygen The front of the detector probe is a composite of fluorescent material foil, the surface coated with a black light-insulating material to avoid sunlight and water Other fluorescent interference, the probe is equipped with an excitation light source and photosensitive components. The blue light shines on the fluorescent substance to make the fluorescent substance Mass excitation and emit red light, as oxygen molecules can take away the energy to reduce the fluorescence intensity (quenching effect), at a certain temperature Degrees, the time and intensity of excited red light is inversely proportional to the concentration of oxygen molecules. By measuring the phase difference between the excited red light and the reference light, And compared with the internal calibration value, calculate the concentration of oxygen molecules. 4.2 measuring range The measuring range of the instrument is 0 mg/L ~ 20 mg/L, the minimum graduation value is ≤0.1 mg/L.

5 equipment structure

5.1 probe 5.1.1 covered electrode method By the cathode, anode, thermometer, electrolyte, etc., with a diaphragm (through oxygen film, such as fluororesin, poly Ethylene, silicone rubber, etc.) to cover the electrode probe with the configuration that the sample does not directly contact the anode and the cathode. The probe cavity should be Support electrolyte, no bubbles, the diaphragm intact. 5.1.2 Fluorescence method By the excitation light source, fluorescent coating, photosensitive components, thermometers and other components. Fluorescent coating is stable under the excitation of blue light Given the fluorescent material, its properties are stable, not easy to oxidize or fall off. 5.2 electronic unit By the converter, batteries, circuits and other components, should have a waterproof drip structure. 5.3 monitor The display can be a monochrome or color display and should have a water-proof drop structure.

6 technical requirements

6.1 Basic requirements 6.1.1 The appearance of the instrument, inspection rules and labeling, packaging, transportation and storage meet the requirements of GB/T 12519. 6.1.2 Reasonable structure, solid product assembly, parts without loosening, plating (coating) layer, no peeling, rust and blistering. 6.1.3 In normal operation, it can work smoothly without any potential safety hazard. 6.1.4 The parts are not easy to produce machinery, circuit failure, no security risk structure. 6.1.5 Do not affect the performance of the instrument due to water infiltration, condensation and so on. 6.1.6 The monitor should be free from stains and damages; the character strokes are uniform and clear; the screen has no hidden corners, dark spots, Bubbles, dark display, hidden planning, do not show, flashing and so on. 6.1.7 The enclosure of the instrument shall meet the IP52 protection grade requirement of GB 4208. 6.2 functional requirements 6.2.1 The instrument can display the time, measurement and system parameters, etc., should be set, calibration, data storage and data transmission Out of function. 6.2.2 easy to carry on a daily basis, weighing less than 5 kg, equipped with portable batteries such as batteries or rechargeable batteries, you can in the wild Foreign Minister time use. External work or charging power supply voltage for the single-phase (220 ± 22) V, the frequency of (50 ± 0.5) Hz, electricity Continuous battery life case should be greater than 2 h, the instrument should be under-voltage instructions. 6.2.3 Temperature compensation requirements. Instrument measurement results are greatly affected by temperature changes, the instrument should be installed in the circuit thermal element Parts automatically compensate for temperature changes. 6.2.4 Air Pressure Compensation Requirement. The measurement result of the instrument is greatly influenced by the change of air pressure. The instrument can install the pressure transmission in the circuit The sensor automatically compensates for air pressure and can also be automatically compensated by manually inputting atmospheric pressure or altitude. 6.2.5 salinity correction requirements. If the determination of sea water, harbor water, such as high salt water, according to the amount of salt to be automatically repaired Positive, can also manually enter the salinity after automatic correction. 6.3 safety requirements 6.3.1 Insulation resistance Power input to the chassis insulation resistance ≥ 5 MΩ. 6.3.2 Dielectric strength Dielectric strength of the phase and the ground can withstand the AC voltage of 1500 V, the frequency of 50 Hz, the time of 1 min test, Not appear alarm, breakdown, flashover and so on. 6.4 Operating Environment Requirements In the ambient temperature is 0 ℃ ~ 50 ℃, the measured water temperature is 0 ℃ ~ 40 ℃, the dissolved oxygen analyzer should be able to work properly.

7 performance indicators and testing methods

7.1 Performance Indicators Portable dissolved oxygen analyzer performance indicators should meet the technical requirements of Table 1. Table 1 portable dissolved oxygen analyzer performance indicators Project performance testing methods Zero tolerance ± 0.1 mg/L 7.6.1 Response time ≤60 s 7.6.2 Indication error ± 0.5 mg/L 7.6.3 Repeatability ≤ 0.2 mg/L 7.6.4 Temperature error ± 0.5 ℃ 7.6.5 The actual water sample alignment error ≤ 0.6 mg/L 7.6.6 7.2 Test conditions 7.2.1 Ambient temperature. 15 ℃ ~ 25 ℃. 7.2.2 Relative humidity. 85% or less. 7.2.3 Supply voltage. AC (220 ± 22) V. 7.2.4 Power frequency. (50 ± 0.5) Hz. 7.2.5 Surrounding environment. no strong magnetic field, electric spark disturbance. 7.3 Instruments and Equipment 7.3.1 constant temperature water bath (tank). Temperature accuracy of ± 0.2 ℃. 7.3.2 Bubbler. porous. 7.3.3 Standard Thermometer. The minimum scale value is 0.1 ℃. 7.3.4 Analysis of the balance. a sense of not more than 0.0001 g. 7.3.5 Stopwatch. The minimum scale is 0.1 s. 7.3.6 Barometer. The minimum scale is 10 Pa. 7.4 Reagents and materials 7.4.1 Test water. distilled water. 7.4.2 Sodium sulfite (Na2SO3). analytical grade. 7.4.3 Bivalent cobalt salts. cobalt (II) chloride hexahydrate (CoCl2 · 6H2O) or other divalent cobalt salts, analytical grade. 7.4.4 Bivalent cobalt salt solution Weigh 0.1 g of bivalent cobalt salt (7.4.3), dissolved in 1% hydrochloric acid, dissolved and then transferred to a 100 ml volumetric flask, add 1% hydrochloric acid to the mark and mix until ready for use. 7.4.5 Anaerobic water Dissolve about 25 g of sodium sulfite (7.4.2) in distilled water at room temperature, add distilled water to 500 ml, add small amount (about 1-2 drops) Bivalent cobalt salt solution (7.4.4), Pro use now. 7.4.6 saturated oxygen water At the specified temperature, the air flow into the distilled water at a flow rate of 1 L/min for more than 2 h to dissolve Oxygen is saturated and allowed to stand for a period of time to stabilize the dissolved oxygen. Note. In general,.200 ml of water needs to be allowed to stand for 5 min to 10 min, 500 ml of water to be allowed to stand for 10 min to 20 min, and GB 7489 to determine if it is saturated if necessary. 7.4.7 Water-saturated air Add about 10 ml of distilled water to a clean 250 ml jar, close the lid, shake rapidly for 30 s, then in the chamber Balanced for 30 min at room temperature to stabilize dissolved oxygen. Note 1. Under equilibrated conditions, the partial pressure of oxygen in water saturated with air equals the partial pressure of oxygen in air saturated with water. Therefore, the probe Calibration in water is the same as calibration in air. Note 2. Dissolved oxygen concentration varies with atmospheric pressure, should be pressure compensation. 7.5 Calibration 7.5.1 Zero point calibration. Depending on the instrument type, for zero calibration, immerse the probe in anaerobic water (7.4.5), set the indicated value Adjust to zero. 7.5.2 Saturated Dissolved Oxygen Calibration. Dip the probe into saturated DO (7.4.6) and gently swirl (no need for fluorescence instrument Move), or place the probe in water-saturated air (7.4.7) until the displayed value is stable. Measure the saturated DO (7.4.6) Or water-saturated air (7.4.7) (accurate to ± 0.1 ° C), adjust the displayed value according to the saturation dissolved oxygen concentration in Appendix A. Note. The membrane electrode dissolved oxygen meter shows the value generally varies with the sample flow rate changes, the probe should be in accordance with the manufacturer's method The surface liquid flow rate (usually not less than 0.3 m/s) remains constant. Measurement, if the actual atmospheric pressure deviates from the standard atmospheric pressure, should be corrected according to formula (1).

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