Turbidity Meter Reading Unstable? QiWei WGZ-1B Troubleshooting Malaysia
Turbidity Meter Reading Unstable Malaysia
Does your turbidity meter show different NTU readings when measuring the same water sample?
An unstable result does not always mean that the instrument is faulty. Turbidity measurement is sensitive to sample preparation, air bubbles, sample-vial condition, particle settling, condensation and calibration practice.
This troubleshooting guide explains the common reasons for inconsistent readings when using the QiWei WGZ-1B Portable Turbidity Meter.
⭐ QiWei WGZ-1B Main Specifications
Measurement parameter: Turbidity
Measuring unit: NTU
Measuring range: 0–200 NTU
Minimum display: 0.1 NTU
Measurement principle: 90° scattered light
Repeatability: ≤1%
Zero drift: ±1%
Power supply: 5 × AA batteries or AC adapter
Portable design
LCD display
Automatic power-off
🔍 Common Causes of Unstable Turbidity Readings
The most common causes include:
Air bubbles inside the sample
Dirty sample vial
Fingerprints on the vial
Scratched or damaged vial
Incorrect vial orientation
Particles settling in the sample
Inconsistent sample mixing
Condensation on the vial
Expired or contaminated turbidity standards
Incorrect calibration procedure
Low battery power
Sample turbidity exceeding the instrument range
1️⃣ Air Bubbles Inside the Sample
Air bubbles scatter light and may be detected as suspended particles.
This can cause:
Higher-than-expected readings
Fluctuating values
Poor repeatability
Differences between two vials containing the same sample
Recommended Action
Avoid shaking the sample aggressively.
Pour the sample slowly into the vial.
Allow visible bubbles to disappear.
Gently tap the vial if necessary.
Measure all samples using the same preparation procedure.
Samples collected from pressurised outlets may require additional time for bubbles to escape.
2️⃣ Fingerprints or Water Droplets on the Vial
The WGZ-1B measures light passing through and scattering from the sample. Any contamination on the outside of the vial can interfere with this optical path.
Recommended Action
Hold the vial near the cap or upper section.
Clean the outside using a lint-free cloth.
Remove fingerprints, oil, dust and water droplets.
Do not insert a wet vial into the measuring chamber.
3️⃣ Scratched or Stained Sample Vial
Scratches and permanent stains can scatter light and produce inconsistent results.
Recommended Action
Inspect the vial under good lighting.
Replace badly scratched, cloudy or stained vials.
Do not clean optical vials using abrasive material.
Keep spare sample vials available.
Use consistent vials when comparing measurement trends.
4️⃣ Incorrect Vial Orientation
Minor differences in the glass surface may affect readings if the vial is inserted in different orientations.
Recommended Action
Follow the instrument’s alignment marking.
Insert the vial in the same orientation for repeated measurements.
Close the measuring compartment properly.
Avoid rotating the vial between repeat tests unless the procedure requires it.
5️⃣ Particles Settling Between Measurements
Larger or denser particles may settle quickly. The first reading may therefore differ from the second reading, even when the instrument is operating correctly.
Recommended Action
Mix the sample gently and consistently.
Avoid creating air bubbles.
Measure within a consistent time after mixing.
Record the sampling and preparation procedure.
Do not compare results measured after different settling periods.
6️⃣ Inconsistent Sample Mixing
Aggressive mixing creates bubbles, while insufficient mixing may leave particles unevenly distributed.
Recommended Action
Develop a repeatable procedure covering:
Mixing method
Mixing duration
Waiting time
Sample volume
Measurement timing
Consistency is especially important when comparing readings from wastewater or environmental water.
7️⃣ Condensation on a Cold Sample Vial
A cold sample taken from a refrigerator or cooled process line may cause moisture to form on the outside of the vial.
Condensation can interfere with the optical measurement.
Recommended Action
Allow the sample to reach a suitable measurement condition.
Wipe away all external moisture.
Check that condensation does not reappear before inserting the vial.
Avoid measuring a wet vial.
8️⃣ Contaminated Sample Vial
Residue from a previous sample can affect the next reading.
Recommended Action
Clean the vial properly after every measurement.
Rinse it with the next sample before filling.
Use separate vials for samples that are oily, coloured or difficult to clean.
Do not return used sample liquid to its original container.
9️⃣ Calibration-Standard Problems
Turbidity standards may change because of contamination, incorrect storage or expiry.
Possible warning signs include:
Calibration cannot be completed
Standard reading is unexpectedly high or low
Readings drift after calibration
Different standards produce illogical results
Recommended Action
Check the standard’s expiry date.
Follow the stated storage requirements.
Avoid contaminating the standard container.
Use clean vials.
Do not mix used standard back into the original bottle.
Confirm whether the standard is ready to use or requires preparation.
🔟 Incorrect Calibration Procedure
Incorrect calibration may affect the entire measuring range.
Recommended Action
Follow the QiWei operating manual.
Use the correct standard concentration.
Clean the vial before calibration.
Remove air bubbles.
Insert the vial consistently.
Allow the instrument and standard to stabilise.
Recheck the standard after calibration.
Do not assume that a successful button sequence guarantees a valid calibration if the standard or vial is contaminated.
🔋 1️⃣1️⃣ Low Battery Power
Weak batteries may contribute to unreliable instrument operation.
Recommended Action
Replace all batteries as a complete set.
Use batteries of the same type and condition.
Check battery contacts for contamination or corrosion.
Compare operation using the AC adapter, where appropriate.
Remove batteries before long-term storage.
📈 1️⃣2️⃣ Sample Exceeds 200 NTU
The WGZ-1B has a stated range of 0–200 NTU.
A sample outside this range may produce an over-range indication or an unreliable result.
Recommended Action
Check whether the sample is visibly very turbid.
Confirm the expected measurement range.
Consider a higher-range turbidity meter.
Use dilution only when supported by a validated procedure.
Consider a suspended-solids meter when the required result is in mg/L.
🧪 Quick Repeatability Check
Use the following procedure to determine whether the problem comes from the instrument, vial or sample:
Prepare one clean vial with a stable sample or suitable standard.
Remove all bubbles and clean the vial exterior.
Mark the vial orientation.
Insert it into the instrument.
Record the result.
Remove and reinsert it in the same orientation.
Repeat the measurement several times.
Compare the results.
If repeatability is acceptable with a stable standard but poor with the actual water sample, the sample preparation or settling behaviour is likely affecting the measurement.
🛠️ When Should the Instrument Be Inspected?
Request technical inspection when:
The instrument cannot power on with new batteries or the correct adapter
The display is incomplete or abnormal
Calibration repeatedly fails with valid standards
Stable standards produce highly inconsistent readings
The measuring chamber is contaminated or damaged
Readings remain abnormal after changing the vial
The instrument was dropped, flooded or exposed to chemicals
Results differ significantly from a trusted reference instrument
Do not dismantle the optical system without suitable technical knowledge.
✅ Preventive-Care Checklist
Before every measurement:
Check the vial for scratches
Rinse the vial with the sample
Remove air bubbles
Wipe the vial exterior
Check the vial orientation
Confirm the sample is within range
After measurement:
Dispose of the sample correctly
Clean and dry the vial
Keep the chamber clean and dry
Store standards correctly
Return the instrument to its carrying case
Record unusual readings or operating conditions
📍 QiWei WGZ-1B Support Malaysia
MTM Precision supplies water-quality testing instruments and provides product-selection assistance for customers in Selangor, Kuala Lumpur, Johor, Penang, Perak, Melaka, Negeri Sembilan, Pahang, Kedah, Perlis, Terengganu, Kelantan, Sabah and Sarawak.
When requesting troubleshooting assistance, provide:
Instrument model
Sample type
Expected turbidity
Actual displayed result
Calibration-standard concentration
Photos or video of the issue
Steps already attempted
📞 Contact MTM Precision
MTM Precision Sdn Bhd
Tel / WhatsApp: +6016-660 7346
Office: +603-8080 7172
Email: mtmpre@yahoo.com
Website: www.mtmpre.com.my
Showroom & Service Centre:
No. 29-1 & 29-2, Jalan Bandar 18,
Pusat Bandar Puchong,
47160 Puchong, Selangor, Malaysia.
Contact MTM Precision for the QiWei WGZ-1B price, availability, spare-vial enquiries, turbidity-standard enquiries and technical support in Malaysia.
15 Sep 2026
