An unstable dissolved oxygen reading does not always mean that the meter is faulty. Movement, temperature changes, bubbles, probe contamination, calibration errors and worn sensing components can all cause the displayed value to fluctuate.

 

When an Azovtes dissolved oxygen meter produces slow, drifting or inconsistent readings, troubleshoot the sampling conditions and sensor systematically before deciding that the instrument requires repair.

 

What Does an Unstable DO Reading Look Like?

 

Common symptoms include:

 

The reading continuously moves up and down

 

The displayed value drifts slowly

 

The result takes unusually long to stabilise

 

Repeated measurements give different results

 

The reading changes after the probe is moved

 

The meter shows an unexpected high or low value

 

The instrument cannot complete calibration

 

The reading does not match known water conditions

 

Small changes may reflect actual variation in the water. Large or continuous fluctuations usually require further investigation.

 

1. The Reading Has Not Had Time to Stabilise

 

A dissolved oxygen probe requires time to adjust to the sample.

 

Stabilisation may take longer when:

 

The probe moves from air into water

 

Sample temperature differs from probe temperature

 

The meter was recently switched on

 

The water has low circulation

 

The sensor is dirty

 

The sensing component is ageing

 

Keep the probe at the required depth and wait for the displayed result to become steady before recording it.

 

Do not record the first number that appears on the screen.

 

2. Water Temperature Is Changing

 

Dissolved oxygen solubility is affected by temperature. If the probe and sample are at different temperatures, both the oxygen response and temperature compensation may continue changing.

 

For better consistency:

 

Place the probe in the sample.

 

Allow the temperature reading to stabilise.

 

Avoid holding the sample container with warm hands.

 

Keep the sample away from direct sunlight.

 

Record the result only after both readings become stable.

 

Rapid temperature changes are especially common when moving between indoor and outdoor sampling locations.

 

3. Air Bubbles Are Attached to the Sensor

 

Air bubbles on the sensing area can produce an incorrect or unstable result.

 

Bubbles may form when:

 

The probe is inserted too quickly

 

The sensor is tilted incorrectly

 

Aerated water is being measured

 

The membrane or sensing surface traps air

 

The probe is placed directly beside an aerator

 

Gently reposition the probe to release bubbles. Do not strike the sensor against the container or tank wall.

 

A bubble attached to the sensor may cause the meter to measure the bubble rather than the surrounding water.

 

4. The Sample Does Not Have Sufficient Movement

 

Some membrane-based dissolved oxygen sensors require water movement across the membrane during measurement.

 

In a stagnant sample, oxygen close to the sensor may be consumed faster than it is replaced, causing the reading to decrease or drift.

 

Depending on the meter and procedure, users may need to:

 

Move the probe gently through the water

 

Stir the sample at a consistent speed

 

Use a laboratory stirrer

 

Measure in naturally flowing water

 

Avoid vigorous movement that introduces new air bubbles into the sample.

 

Fluorescence-based DO meters are generally less dependent on sample movement, but the probe must still be positioned correctly.

 

5. The Probe Is Dirty

 

Wastewater, pond water and industrial samples can leave deposits on the sensor.

 

Common contaminants include:

 

Algae

 

Biofilm

 

Sludge

 

Oil

 

Grease

 

Minerals

 

Chemical residue

 

Fine suspended particles

 

A coated sensor may respond slowly or produce inconsistent readings.

 

Clean the probe according to the manufacturer’s instructions. Do not scrape a membrane or optical sensing surface with sharp tools.

 

6. The Membrane Is Damaged

 

For membrane-type meters such as the Azovtes JE8803, inspect the membrane for:

 

Tears

 

Wrinkles

 

Punctures

 

Looseness

 

Discolouration

 

Deposits

 

Trapped air bubbles

 

Incorrect installation

 

A damaged or poorly installed membrane should be replaced. After replacement, the sensor may require preparation, polarisation and recalibration before use.

 

7. The Electrolyte Requires Attention

 

Electrochemical DO probes commonly use electrolyte. Reading problems may occur when:

 

Electrolyte is insufficient

 

Electrolyte is contaminated

 

The electrolyte has deteriorated

 

Air bubbles are trapped inside

 

The wrong electrolyte is used

 

The probe was assembled incorrectly

 

Use only the correct consumable specified for the sensor.

 

Adding more electrolyte without inspecting the membrane and electrode may not solve the problem.

 

8. The Fluorescence Sensor Cap Is Dirty or Ageing

 

For fluorescence-based meters such as the Azovtes JE8803A, examine the optical sensing area.

 

Potential problems include:

 

Biofilm on the sensor cap

 

Oil or chemical deposits

 

Scratched sensing material

 

Ageing fluorescent coating

 

Incorrectly installed sensor cap

 

Moisture or contamination inside the assembly

 

Clean the sensing surface gently using the recommended method. Replace the sensor cap when it reaches the manufacturer’s replacement condition.

 

9. Calibration Was Not Performed Correctly

 

Incorrect calibration can cause the meter to drift or display unrealistic results.

 

Check whether:

 

The correct calibration mode was selected

 

The calibration environment was suitable

 

The probe was stable during calibration

 

The sensor was clean

 

Temperature had stabilised

 

Required compensation settings were correct

 

Calibration was completed successfully

 

If the calibration repeatedly fails, inspect the probe and consumables before attempting it again.

 

10. Salinity or Atmospheric Pressure Was Ignored

 

Dissolved oxygen calculations may be affected by salt content and atmospheric pressure.

 

This is particularly relevant for:

 

Seawater

 

Brackish water

 

Shrimp farms

 

Coastal monitoring

 

High-altitude locations

 

Pressurised systems

 

If the instrument provides compensation settings, enter the correct values according to the testing procedure.

 

11. The Sampling Method Is Inconsistent

 

Two results may differ because the samples were not taken under the same conditions.

 

Check whether measurements were made at the same:

 

Location

 

Depth

 

Time of day

 

Distance from the aerator

 

Water temperature

 

Flow condition

 

Weather condition

 

Probe movement rate

 

In aquaculture and wastewater tanks, different readings may represent genuine variation across the water body.

 

Quick Troubleshooting Sequence

 

When the DO reading is unstable, follow this order:

 

Allow more stabilisation time.

 

Check temperature stability.

 

Remove attached air bubbles.

 

Confirm the required sample movement.

 

Clean the sensor.

 

Inspect the membrane or optical cap.

 

Check the electrolyte where applicable.

 

Recalibrate the meter.

 

Verify salinity and pressure settings.

 

Test the instrument in a controlled sample.

 

Compare with another maintained DO meter if available.

 

This sequence helps separate operating problems from sensor or instrument faults.

 

When Should the Probe Be Replaced?

 

Probe servicing or replacement may be necessary when:

 

Calibration repeatedly fails

 

Readings remain unstable after cleaning

 

The membrane is frequently damaged

 

The electrode is deteriorated

 

The fluorescence cap has reached its service life

 

The sensor response remains extremely slow

 

Results remain unreasonable in controlled conditions

 

Replacement consumables do not solve the problem

 

Before replacing the complete instrument, determine whether the issue is limited to the sensing component.

 

How to Prevent Unstable Readings

 

Good preventive practices include:

 

Rinse the probe after every test

 

Clean it according to the sample condition

 

Inspect consumables regularly

 

Store the probe correctly

 

Calibrate before important measurements

 

Avoid impact on the sensing area

 

Keep a maintenance record

 

Train operators to use the same sampling method

 

Record measurement time, depth and temperature

 

Keep replacement consumables available

 

Consistent maintenance and sampling procedures are the most effective ways to improve dissolved oxygen measurement reliability.

 

Azovtes Dissolved Oxygen Meter Support Malaysia

 

MTM Precision supplies Azovtes dissolved oxygen and water-quality meters for aquaculture, wastewater, environmental and industrial applications across Malaysia.

 

Coverage includes Selangor, Kuala Lumpur, Johor, Penang, Perak, Melaka, Negeri Sembilan, Pahang, Kedah, Perlis, Terengganu, Kelantan, Sabah and Sarawak.

 

Contact MTM Precision

 

MTM Precision Sdn Bhd

Website: www.mtmpre.com.my

Email: mtmpre@yahoo.com

WhatsApp: 016-660 7346

 

Showroom & Service Centre

 

No. 29-1 & 29-2, Jalan Bandar 18,

Pusat Bandar Puchong,

47160 Puchong, Selangor, Malaysia

 

Contact MTM Precision for help selecting or troubleshooting an Azovtes dissolved oxygen meter in Malaysia.