Why Two Temtop PM2.5 Monitors Show Different Readings Malaysia
Why Two Temtop PM2.5 Monitors Show Different Readings Malaysia
Two Temtop PM2.5 monitors placed in the same room may not always display exactly the same number.
A small difference does not automatically mean that one instrument is faulty.
PM2.5 changes continuously, and two monitors may sample the surrounding air at slightly different times, positions, or operating modes.
Before requesting repair or replacement, perform a controlled comparison.
Why PM2.5 Readings Change Quickly
Indoor air is not perfectly mixed.
Particle concentration may be different near:
- An open window.
- A doorway.
- An air conditioner outlet.
- An air purifier.
- A cooking area.
- A smoking area.
- A loading bay.
- A busy road.
- A person walking through the room.
- A recently cleaned surface.
Even when two monitors are only a short distance apart, they may be sampling different air movement.
1. The Monitors Are in Different Positions
Position is one of the most common reasons for different readings.
For example, one monitor may be:
- Closer to the air purifier.
- Nearer to an open window.
- Directly under an air conditioner.
- Beside a wall.
- Near a door that opens frequently.
- Close to a particle source.
Move both instruments to the same stable table and place them beside each other without blocking either air inlet.
Do not stack one monitor on top of the other.
2. The Air Inlet Is Blocked
A PM2.5 monitor needs unrestricted airflow around its sensor inlet.
Readings may be affected when the monitor is:
- Placed against a wall.
- Covered by paper or fabric.
- Inside a closed cabinet.
- Held with a hand over the inlet.
- Positioned too close to another instrument.
- Surrounded by dust.
Check that the inlet and outlet areas are not blocked.
Do not insert objects into the sensor opening or use compressed air unless the manufacturer specifically permits it.
3. The Instruments Update at Different Times
Different Temtop models may not refresh their displays at exactly the same time.
For example, the S1 Up, P600, M10+, M2000 2nd, and LKC-1000S 2nd are designed for different monitoring applications.
One model may update rapidly for spot checking, while another may use averaging or a power saving cycle.
During a sudden PM2.5 change, one unit may respond before the other. The readings may become closer after the room condition stabilises.
4. One Monitor Is in a Power Saving Mode
Some monitors use different operating modes to reduce battery consumption.
A power saving mode may sample less frequently than an active measurement mode.
Before comparing two units:
- Check the operating mode.
- Confirm that both units are actively measuring.
- Charge or replace the battery if necessary.
- Allow both instruments to operate for a suitable period.
- Avoid comparing an active mode with an energy saving mode.
5. The Monitors Were Just Moved
A monitor carried from outdoors into an air-conditioned room may need time to respond to the new environment.
The same applies when moving between:
- A hazy outdoor area and a cleaner room.
- A warm warehouse and a cool office.
- A humid area and an air-conditioned space.
- A kitchen and a bedroom.
- A guardhouse and a factory office.
Allow both instruments to stabilise in the same location before comparing them.
6. Particle Levels Are Changing During the Test
Cooking, sweeping, smoking, spraying, and opening doors can cause particle readings to change quickly.
Walking close to the monitor may also disturb settled dust.
For a better comparison:
- Stop cooking.
- Avoid smoking.
- Do not sweep or vacuum.
- Keep doors and windows in the same condition.
- Keep the air purifier at one fixed setting.
- Limit unnecessary movement.
- Wait for the room condition to become more stable.
Do not compare two monitors while one is being carried around the room.
7. The Air Purifier Affects One Monitor More Than the Other
A monitor placed directly beside the purifier outlet may show a lower reading than another monitor positioned farther away.
This does not necessarily represent the average condition of the room.
For purifier testing:
- Place both monitors beside each other.
- Keep them away from the direct outlet airflow.
- Record the starting readings.
- Start the purifier.
- Keep doors and windows unchanged.
- Observe the trend over time.
- Compare whether both readings generally move in the same direction.
The two numbers may not be identical, but both should normally show the same general trend when conditions are controlled.
8. Sensor Tolerance and Unit Variation
Two electronic sensors may have a reasonable difference even when they are operating correctly.
Consumer and portable indoor air quality monitors should not be expected to produce perfectly identical readings at every moment.
A useful comparison should consider:
- The size of the difference.
- Whether the difference remains consistent.
- Whether both readings rise and fall together.
- Whether the same unit is always unusually high or low.
- Whether the difference continues under stable conditions.
A one-second comparison is not enough to judge sensor performance.
9. Dust or Contamination May Affect the Sensor
Long-term exposure to dusty environments may affect airflow through the sensor.
Possible signs include:
- A reading that remains unusually high in clean air.
- A reading that does not respond when moved.
- Very slow response.
- Repeated abnormal spikes.
- A large difference from another unit under controlled conditions.
Do not open the instrument or clean the internal sensor without proper instructions. Incorrect cleaning may damage the fan, optics, or sensor chamber.
10. High Humidity or Condensation
High humidity and condensation may affect some particle measurements.
Avoid:
- Testing immediately after moving a cold instrument into warm humid air.
- Placing the monitor beside a humidifier.
- Exposing the unit to mist.
- Using it in rain.
- Testing directly above boiling water.
- Storing it in a damp location.
If condensation is suspected, switch off the instrument and allow it to return to a suitable dry indoor condition before using it again.
How to Compare Two PM2.5 Monitors Correctly
Use this controlled procedure:
Step 1: Confirm the Models
Record the complete model names.
Different Temtop models may use different settings, display behaviour, and measurement cycles.
Step 2: Check the Air Inlets
Make sure both instruments are clean, uncovered, and undamaged.
Step 3: Check the Operating Modes
Use active measurement modes where available.
Step 4: Place Them Side by Side
Use the same table, measurement height, and room location.
Leave enough space so that one unit does not block the airflow of the other.
Step 5: Control the Room
Keep doors, windows, air conditioner settings, and purifier settings unchanged.
Avoid cooking, cleaning, smoking, and spraying.
Step 6: Allow the Readings to Stabilise
Do not judge the instruments immediately after moving or switching them on.
Step 7: Record Several Readings
Record both displays at regular intervals.
Step 8: Compare the Trend
Check whether both readings increase and decrease together.
The trend may be more informative than expecting both displays to show the same number.
When Should the Monitor Be Checked?
Further inspection may be appropriate when:
- One unit does not respond to changing air conditions.
- One reading remains extremely high in a clean room.
- One reading remains at zero in visibly smoky or dusty conditions.
- The fan produces an unusual sound.
- The display shows an error.
- The unit switches off unexpectedly.
- The battery does not charge.
- A large difference remains after a controlled comparison.
- The monitor has been exposed to water, impact, or heavy dust.
Before sending the instrument for assessment, take a clear photo or short video showing:
- The model label.
- Both monitors in the same position.
- The displayed readings.
- The operating mode.
- The visible error or symptom.
- The time allowed for comparison.
Checking Is Not the Same as Calibration
Placing two monitors together is a comparison check.
It can show whether the instruments respond similarly, but it does not establish measurement accuracy against a traceable reference.
Calibration requires comparison against an appropriate reference using a defined method and controlled conditions.
A difference between two portable monitors does not automatically prove which unit is correct.
Avoid These Comparison Mistakes
Do not:
- Compare one monitor indoors and another outdoors.
- Place one beside a purifier outlet.
- Hold one monitor while the other remains on a table.
- Compare different operating modes.
- Judge the result immediately after switching on.
- Test during cooking or cleaning.
- Block the sensor inlet.
- Expect both displays to change at the same second.
- Open the instrument without proper instructions.
- Treat a comparison as formal calibration.
Temtop Air Quality Monitor Support in Malaysia
A controlled side-by-side comparison can solve many apparent PM2.5 reading problems.
If a large difference remains, contact MTM Precision for an initial assessment. WhatsApp a clear instrument photo, model label, comparison setup, displayed readings, and visible error or symptom.
MTM Precision Sdn Bhd
Showroom and Service Centre: No. 29-1 and 29-2, Jalan Bandar 18, Pusat Bandar Puchong, 47160 Puchong, Selangor, Malaysia
Tel: 03-8080 7172
WhatsApp: +6016-660 7346
Email: mtmpre@yahoo.com
Website: www.mtmpre.com.my
07 Oct 2026
