Measurement Key Points

Turbidity measurement is an important indicator in water quality testing. Accurate turbidity measurement is crucial for drinking water safety, environmental monitoring, and water treatment process control. This article details the operation steps and precautions for various measurement methods.

1. Overview of Turbidity Measurement Methods

Turbidity measurement is mainly based on optical principles, determining water turbidity by measuring the degree of light scattering or absorption by suspended particles in water. Common measurement methods include:

Laboratory Turbidimeter Method


1. Laboratory Turbidimeter Method

The most accurate method, based on 90° light scattering principle, complies with international standard ISO 7027. Measurement range: 0-1000 NTU, accuracy up to ±0.1 NTU.

2. Portable Turbidimeter Method

Suitable for field testing, simple operation, fast measurement speed. Measurement range: 0-1000 NTU, accuracy generally ±0.5 NTU.

3. Visual Comparison Method

Traditional method, estimating turbidity by comparing visual clarity of water sample with standard turbidity tubes. Lower accuracy, suitable for rapid estimation.

2. Laboratory Turbidimeter Measurement Steps

Standard operation procedure for measuring water turbidity using a laboratory turbidimeter:

Sample Preparation


1

Sample Preparation

Collect representative water sample, mix thoroughly (avoid vigorous shaking creating bubbles). If water sample contains large particles, let stand or filter first.

2

Equipment Warm-up and Inspection

Turn on turbidimeter power, warm up for 15-30 minutes. Check if sample cell is clean without scratches, ensure instrument is working normally.

3

Instrument Calibration

Calibrate using standard turbidity solutions:

  • Zero calibration: Use zero turbidity water (distilled water or deionized water)
  • Range calibration: Use standard turbidity solutions (such as 20 NTU, 100 NTU)

Calibration frequency: Before daily use or after continuous measurement exceeding 4 hours, recalibrate.

4

Sample Measurement

Pour water sample into clean sample cell to marked line, wipe outer wall clean with lint-free cloth, place into measurement chamber, close lid, read and record turbidity value.

5

Result Recording and Equipment Maintenance

Record measurement value, unit, measurement time, sample information, etc. Clean sample cell immediately after measurement, maintain instrument regularly.

3. Measurement Equipment Selection Guide

Different application scenarios require different types of turbidity measurement equipment:

Equipment Type Measurement Range Accuracy Application Scenarios Reference Price
Laboratory Turbidimeter 0-1000 NTU ±0.1 NTU Laboratory, Quality Control Center $700-4,200
Portable Turbidimeter 0-1000 NTU ±0.5 NTU Field Testing, Inspection $300-1,200
Online Turbidity Meter 0-100 NTU ±1% FS Water Treatment Process Monitoring $1,200-3,000
Turbidity Colorimeter 1-100 NTU ±5% Teaching, Rapid Screening $70-300

4. Common Problems and Solutions

Problem 1: Unstable measurement results, values fluctuating greatly

Possible causes: Bubbles in sample; Dirty sample cell; Insufficient instrument warm-up; Environmental light interference.

Solutions: Let sample stand to eliminate bubbles; Clean sample cell; Warm up for over 30 minutes; Avoid strong light environment for measurement.

Problem 2: Measurement values always high or low

Possible causes: Incorrect instrument calibration; Expired standard solution; Scratched sample cell.

Solutions: Recalibrate instrument; Use standard solutions within validity period; Replace unscratched sample cell.

Problem 3: Large differences in results from different instruments measuring same sample

Possible causes: Different instrument principles; Inconsistent calibration standards; Operator differences.

Solutions: Unify to use scattered light method instruments; Use same batch standard solutions for calibration; Unified operation training.

5. Measurement Quality Control Requirements

To ensure accuracy and reliability of measurement results, establish a comprehensive quality control system:

  1. Regular calibration: Perform zero calibration before daily use, range calibration weekly
  2. Parallel sample testing: Perform at least 10% parallel samples per batch, relative deviation should be less than 5%
  3. Reference material verification: Regularly verify instrument accuracy using certified reference materials
  4. Personnel training: Operators need professional training and pass assessments
  5. Equipment maintenance: Establish equipment maintenance records, regular cleaning and maintenance

Measurement Precautions

  • Ensure sample temperature matches ambient temperature before measurement
  • Avoid measuring near strong magnetic or electric fields
  • Regularly replace light sources and detectors (according to instrument requirements)
  • Establish complete measurement record archives
  • Participate in inter-laboratory comparisons and proficiency testing