I. Overview

　　Automatic water quality samplerIt is used forAutomatically collect, save, and transmit water samplesThe instrument equipment is widely used in environmental monitoring stations, sewage treatment plants, industrial sewage outlets, water source protection and other fields, and is a key tool for water quality monitoring and pollution tracing. Its core function is to automatically collect representative water samples according to preset programs (such as time intervals, flow ratios, event triggers, etc.), and maintain water sample stability through refrigeration, adding preservatives, etc., providing reliable samples for subsequent laboratory analysis (such as heavy metal, organic matter, nutrient and other indicator detection).

With the improvement of environmental regulatory requirements (such as China's Water Pollution Prevention and Control Law and Ecological Environment Monitoring Network Construction Plan) and the development of online monitoring technology, automatic water quality samplers need to meet the requirements ofHigh precision, high reliability, intelligence, and complianceRequirement. This article is based on relevant domestic and foreign standards (such as HJ/T 372-2007 "Technical Requirements and Testing Methods for Water Quality Automatic Samplers", HJ 353-2019 "Technical Specifications for Installation of Online Monitoring Systems for Water Pollution Sources", etc.), systematically elaborating on their technical requirements and testing methods.

2、 Technical requirements

The technical requirements for automatic water quality samplers coverBasic functions, performance indicators, environmental adaptability, safety and reliabilityThe four dimensions are as follows:

Indicator Category	Specific requirements (refer to HJ/T 372-2007 and industry practices)
​Sampling accuracy​	Single sampling error ≤ ± 5% (or absolute error ≤ ± 2 mL, take the stricter value); Flow measurement error during proportional sampling is ≤± 2% (matched with the matching flowmeter)
​Time accuracy​	Timing sampling time error ≤± 1% (or absolute error ≤± 1 minute/day)
​Temperature control​	The temperature of the water sample is maintained at 2-5 ℃ (fluctuation ≤± 2 ℃) in refrigeration mode, and the fluctuation of the -20 ℃ model is ≤± 3 ℃
​Pipeline system​	Using inert materials (such as PTFE, silicone, stainless steel), resistant to pH 1-14 acid-base solutions and organic solvents; Inner diameter of pipeline ≤ 2 mm (to reduce residue and adsorption)
​Repeatability​	When conducting equal sampling multiple times (≥ 5 times) in a row, the relative standard deviation of a single sampling amount is ≤ 2%
​Response time​	The delay of event triggered sampling from signal input to start sampling is ≤ 10 seconds (faster in emergency situations)

（1） Basic functional requirements

​Diversity of sampling modes​

​Timed samplingCollect fixed volume water samples at preset time intervals (such as hourly or daily) (with a single sampling volume typically ranging from 5 to 500 mL and adjustable);

​Traffic ratio samplingCollect water samples proportionally based on flow meter signals (such as electromagnetic flow meters, ultrasonic flow meters) (e.g. collect 10 mL for every 10 m ³ increase in flow rate), suitable for dynamic monitoring of sewage outlets;

​Equal time mixed samplingCollect multiple water samples within a set time period (such as 24 hours) and mix them (such as taking one sample every hour, and finally mixing into one 24-hour comprehensive sample);

​Event triggered samplingImmediately collect water samples in response to external signals (such as over limit alarms, water quality sudden change sensor signals) for emergency monitoring of pollution accidents;

​Remote control samplingSupport receiving remote commands through wireless communication (such as 4G/5G, NB IoT) or wired networks (such as sampling commands issued by environmental protection department platforms).

​Water sample preservation and pretreatment​

​Refrigeration functionEquipped with a built-in compressor or semiconductor refrigeration module, the water sample storage temperature is controlled at 2-5 ℃ (some models can reach -20 ℃) to delay microbial activity and chemical reactions;

​Add preservativeSupport automatic addition of fixatives (such as hydrochloric acid, nitric acid, sodium hydroxide, etc., used to adjust pH or stabilize heavy metals/organic compounds), and the type and dosage of preservatives can be programmed;

​Anti pollution designSampling bottles (usually made of polyethylene, glass, or stainless steel) are sealed with sealed caps or inert materials to prevent external impurities from entering; Some models are equipped with automatic cleaning function (rinse the pipeline with pure water before and after sampling).

​Intelligent Control and Data Management​

​Programmed settingsSet sampling parameters (time, volume, mode, etc.) through touch screen or upper computer software, and support switching between multiple preset programs;

​Data storage and transmissionRecord sampling time, volume, mode, fault information and other logs (storage capacity ≥ 10000), which can be uploaded to the monitoring platform through RS-232/485, Ethernet or wireless communication;

​Fault alarmWhen there is a shortage of water, pipeline blockage, refrigeration failure, abnormal power supply, etc., sound and light alarms or remote message prompts will be used.

（2） Performance indicator requirements

（3） Environmental adaptability requirements

​Temperature rangeWorking environment temperature -10~40 ℃ (some outdoor models can tolerate -20~50 ℃);

​Humidity rangeRelative humidity ≤ 90% (no condensation);

​Protection levelOutdoor installation models must reach IP65 or above (dustproof and waterproof, preventing rainwater and dust from entering);

​Anti-interference abilityCapable of withstanding electric field interference of 50 Hz/100 V/m, magnetic field interference of 10 V/m, and mechanical vibration (compliant with GB/T 17626 series electromagnetic compatibility standards).

（4） Safety and reliability requirements

​Electrical safetyGrounding resistance ≤ 4 Ω, insulation resistance ≥ 100 M Ω (to prevent leakage risk);

​​材料安全性​Components that come into contact with water samples, such as pipelines and sampling bottles, must comply with food grade or analytical grade standards (to avoid releasing toxic substances that contaminate water samples);

​Service lifeKey components (such as pumps, valves, refrigeration modules) are designed to have a lifespan of ≥ 3 years and an average time between failures (MTBF) of ≥ 5000 hours;

​Power outage protectionSupport UPS uninterruptible power supply or built-in battery (maintain refrigeration and data storage for ≥ 72 hours), automatically save current parameters and sampling records after power failure.

3、 Testing method

The detection of water quality automatic sampler needs to be carried out inStandard environmental conditionsThe testing is conducted at a temperature of 20 ± 2 ℃ and a relative humidity of 45%~55%. The testing items cover functional verification, performance index testing, environmental adaptability assessment, and safety and reliability evaluation. The specific methods are as follows:

（1） Basic function testing

​Sampling mode validation​

​Timed samplingSet a fixed time interval (e.g. every 30 minutes), start the sampler and record the deviation between the actual sampling time point and the preset value (timed with a high-precision stopwatch);

​Traffic ratio samplingConnect a standard flow meter (accuracy ≤± 0.5%), simulate different flow rates (such as 5 m ³/h, 20 m ³/h), and verify whether the proportional relationship between sampling volume and flow rate meets the set value;

​Event triggered samplingTrigger sampling through an external signal generator (such as a relay simulating an over limit signal) to detect the delay time from signal input to the start of sampling (recorded with an oscilloscope or data acquisition instrument).

​Water sample preservation function testing​

​Refrigeration effectPlace the sampler in a room temperature environment, start cooling, and measure the temperature of the water sample every 10 minutes (using a precision thermometer) until the temperature stabilizes at 2-5 ℃ (fluctuation of ≤± 2 ℃ is considered qualified);

​Preservation agent additionVerify the added amount through weighing or titration method (e.g. set to add 5 mL hydrochloric acid, actual measurement of added volume error ≤± 2%).

（2） Performance indicator testing

​Sampling accuracy test​

Measure the volume of a single sample directly using a standard measuring cylinder (accuracy ± 0.1 mL) or an electronic balance (accuracy ± 0.01 g, water density 1 g/mL), take 10 consecutive samples, calculate the average value and single error (error=| single value - average value |/average value × 100%), with a requirement of ≤± 5%;

When performing proportional sampling, synchronously record the flow meter signal and sampling volume, calculate the linear correlation coefficient (R ² ≥ 0.999) and proportional error (≤± 2%) between flow rate and sampling volume.

​Time accuracy testing​

Set up a timed sampling program (such as hourly sampling), run continuously for 24 hours, and record the deviation between the actual sampling time and the theoretical time (error=| actual time - theoretical time |/theoretical time × 100%), with a requirement of ≤± 1%.

​Temperature control test​

In refrigeration mode, place the temperature sensor (with an accuracy of ± 0.1 ℃) near the sampling bottle, record the water temperature every 5 minutes, monitor continuously for 2 hours, and calculate the temperature fluctuation range (maximum minimum), with a requirement of ≤± 2 ℃.

​Repetitive testing​

Perform 10 consecutive equal samplings (e.g. 50 mL each time), weigh the mass of each sampled water sample using a precision balance, and calculate the relative standard deviation (RSD=standard deviation/mean x 100%), with a requirement of ≤ 2%.

（3） Environmental adaptability testing (optional, for special scenarios)

​High/low temperature testingPlace the sampler in a high and low temperature test chamber (such as -10 ℃ or 40 ℃), stabilize for 2 hours, and test whether the basic functions (such as sampling, cooling, and data transmission) are normal;

​Humidity testPlace in an environment with a humidity of 95% ± 3% for 48 hours and check for condensation in the pipeline and short circuits in the circuit;

​Vibration testingSimulate transportation vibrations (frequency 10-50 Hz, acceleration 1-5 g) to detect the structural integrity and parameter stability of the sampler.

（4） Safety and reliability testing

​Electrical safetyMeasure the insulation resistance (≥ 100 M Ω) between the power cord and the casing using an insulation resistance tester, and measure the grounding resistance (≤ 4 Ω) using a grounding resistance tester;

​Power outage protectionManually cut off the main power supply and observe whether the refrigeration module maintains operation (≥ 72 hours) and whether the sampling records are lost (verified through stored data);

​​材料安全性​Soak the sampling bottle in pure water for 24 hours, and detect the content of heavy metals (such as lead and cadmium) and organic compounds (such as VOCs) in the soaking solution (which should be lower than the limit values of GB/T 14848-2017 "Groundwater Quality Standards").

4、 Summary and Prospect

The automatic water quality sampler is the core equipment of the water quality monitoring system, and its technical requirements revolve aroundAccurate sampling, reliable storage, intelligent control, and environmental adaptationThe testing method must strictly follow the standards to ensure that the equipment meets compliance and scientific requirements in practical applications.

In the future, with the development of online monitoring technology, automatic water quality samplers will move towardsMulti functional integration (such as multi parameter online analysis linkage), miniaturization (portable emergency sampling), intelligence (AI adaptive sampling strategy)The direction of evolution requires further optimization of material anti pollution performance (reducing water sample residue and adsorption interference) and low-power design (adapting to power supply limitations in remote areas), providing stronger technical support for precise water environment management.

​Note:When conducting actual testing and acceptance, it is necessary to combine specific standard versions (such as the latest version of HJ/T 372 or local environmental protection department requirements) and equipment manual parameters.