Why NOYAFA JMS11 or JMS12 HCHO and TVOC Readings Keep Changing Malaysia
Why Do HCHO and TVOC Readings Keep Changing?
The readings displayed by a NOYAFA JMS11 or JMS12 may rise, fall or fluctuate when the detector is moved between rooms or exposed to different indoor conditions.
This does not automatically mean that the instrument is defective.
HCHO and TVOC readings may be influenced by:
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Ventilation
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Room temperature
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Relative humidity
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Perfume
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Alcohol and sanitiser
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Cleaning chemicals
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Paint and adhesive
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New furniture
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Air-conditioner operation
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The position of the detector
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Insufficient stabilisation time
Understanding these factors helps users obtain more consistent and meaningful results.
Reason 1: The Detector Has Not Stabilised
The sensor requires time to respond to the surrounding air.
A reading taken immediately after:
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Switching on the instrument
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Moving it from outdoors to indoors
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Entering another room
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Removing it from a bag
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Taking it out of a cabinet
may not represent the final condition at that location.
What to do
Place the tester in one position and allow the displayed values to stabilise before recording the result.
Avoid continuously carrying the instrument around while trying to obtain a fixed reading.
Reason 2: The Room Ventilation Has Changed
Opening or closing doors and windows can quickly change the concentration of volatile compounds in a room.
When a room remains closed:
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Indoor pollutants may accumulate.
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Temperature may rise.
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Air exchange may decrease.
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Emissions from materials may become more noticeable.
After opening the windows, outdoor air may dilute the indoor pollutants and cause the displayed reading to decrease.
What to do
When comparing results, record whether:
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Windows were open or closed
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Doors were open or closed
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An exhaust fan was operating
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Mechanical ventilation was running
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The room had remained closed overnight
Compare readings only when the room conditions are clearly documented.
Reason 3: Perfume or Air Freshener Is Nearby
Perfume, deodoriser and air freshener release volatile compounds.
A semiconductor gas sensor may respond to these vapours, causing the TVOC or HCHO-related reading to increase temporarily.
What to do
Avoid applying perfume or spraying fragrance near the tester. Remove the product, ventilate the area and repeat the test after the room has stabilised.
Do not use an air freshener to cover a chemical smell immediately before conducting an air quality test.
Reason 4: Alcohol or Hand Sanitiser Affects the Sensor
Alcohol-based sanitiser is a common source of sudden high readings.
If a user applies sanitiser and then handles the instrument, alcohol vapour may reach the sensor directly.
This may cause:
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A sudden increase
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An alarm
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A reading that takes time to decrease
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A different result from another instrument located farther away
What to do
Keep alcohol, sanitiser and disinfectant away from the detector during testing.
If exposure occurs:
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Move the detector to clean, ventilated air.
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Allow the sensor to recover.
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Avoid breathing or blowing directly into the air inlet.
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Repeat the measurement after the reading stabilises.
Reason 5: Cleaning Chemicals Were Recently Used
Floor cleaner, glass cleaner, furniture polish, detergent, solvent and aerosol products may release volatile compounds.
Testing immediately after cleaning may produce a higher reading than usual.
What to do
Record that cleaning was performed. Ventilate the room and repeat the measurement later.
If the purpose is to evaluate normal room conditions, do not test during or immediately after chemical cleaning.
Reason 6: Temperature Has Increased
Some building and furniture materials may release volatile compounds more rapidly at higher temperatures.
A closed room measured during a hot afternoon may therefore show a higher reading than the same room measured during a cooler morning.
This is one reason why readings should be compared at similar times and under similar conditions.
JMS12 advantage
The NOYAFA JMS12 displays temperature and humidity together with HCHO and TVOC. This makes it easier to identify whether changing environmental conditions may be associated with a changing gas reading.
Reason 7: Humidity Has Changed
High humidity, condensation or a sudden environmental change may affect sensor response and the behaviour of pollutants in the room.
For example, a detector moved from an air-conditioned office to a warm, humid outdoor area may require time to adjust.
What to do
Avoid recording the result immediately after a large temperature or humidity transition.
Allow the detector and the surrounding environment to stabilise before taking the next measurement.
Reason 8: The Detector Is Too Close to the Source
A detector positioned directly beside:
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Wet paint
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Adhesive
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Solvent
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A new cabinet panel
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Cleaning liquid
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An open chemical container
may display a much higher reading than when it is placed in the centre of the room.
Both readings may be useful, but they answer different questions.
General room test
Place the detector in an open position that represents the occupied area.
Source-investigation test
Place the detector closer to the suspected material to compare relative changes.
Do not present a source-level reading as though it represents the entire room.
Reason 9: The Air Inlet Is Blocked
The ventilation openings allow surrounding air to reach the sensor.
The result may respond slowly or inconsistently if the instrument is:
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Held tightly in the hand
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Covered by a cloth
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Placed inside a closed bag
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Pressed directly against a wall
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Positioned on a soft surface that blocks the opening
What to do
Place the tester on a stable surface and keep all ventilation openings unobstructed.
Reason 10: The User Is Breathing Directly onto the Sensor
Human breath contains moisture, carbon dioxide and other compounds. Breathing or speaking directly into the sensor inlet may temporarily influence the displayed values.
What to do
Place the detector on a table rather than holding it directly in front of the face.
Avoid blowing into the ventilation opening to test whether the sensor is responding.
Why Do Two Rooms Produce Different Readings?
Two rooms in the same house may contain different:
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Furniture materials
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Flooring
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Paint
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Adhesives
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Cleaning products
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Ventilation rates
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Temperatures
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Humidity levels
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Air-conditioning conditions
A bedroom with a new built-in wardrobe may produce a different reading from a living room containing older furniture.
This difference can help identify where further investigation is needed.
For a useful comparison:
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Use the same detector.
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Use a similar measuring position.
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Allow the same stabilisation time.
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Record the temperature and ventilation condition.
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Repeat the measurement.
Why Do JMS11 and JMS12 Show Different Numbers?
Two portable detectors may not display exactly the same value because of:
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Different sensor characteristics
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Individual sensor tolerance
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Different sensor age
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Different warm-up or stabilisation time
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Different placement
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Different exposure history
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Air movement across each detector
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Environmental interference
Do not expect two entry-level semiconductor detectors to produce perfectly identical readings at every moment.
Instead, use them consistently to observe general patterns and changes.
For formal verification, use the appropriate professional reference method or calibrated equipment.
Why Does the Reading Rise Inside a Cabinet?
A closed cabinet has a smaller volume and limited air exchange. Volatile compounds released by its panels, adhesive or finishing materials may accumulate inside.
A reading inside a cabinet may therefore be significantly higher than the general room reading.
This does not mean that the cabinet reading represents the concentration throughout the bedroom.
Record the two measurements separately:
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General room reading
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Inside-cabinet reading
Ventilate the cabinet and room before repeating the comparison.
Why Does the Reading Fall and Then Rise Again?
This pattern may occur when:
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The room is ventilated and the reading decreases.
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The doors and windows are closed.
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Volatile compounds continue to be released from indoor materials.
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The concentration gradually increases again.
Repeat the test over several days to determine whether the pattern is consistent.
If readings remain elevated or occupants experience discomfort, consider obtaining a professional assessment.
Is a Changing Reading Evidence of a Faulty Sensor?
Not necessarily.
A changing reading is expected when the surrounding air changes. Before concluding that the sensor is faulty, check whether:
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Perfume was used
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Sanitiser was nearby
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Cleaning had just been completed
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Doors or windows were opened
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The air conditioner was switched on or off
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The detector was moved
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Temperature or humidity changed
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The sensor had enough time to stabilise
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The air inlet was obstructed
A possible instrument problem should be considered if the detector:
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Does not power on
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Cannot charge correctly
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Shows an error continuously
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Does not respond to any environmental change
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Remains at an abnormal value after extended recovery in clean air
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Has been exposed directly to liquid or concentrated chemicals
How to Obtain More Repeatable Results
Use the following method whenever you want to compare readings:
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Use the same instrument.
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Test at the same location.
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Place it at approximately the same height.
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Use the same stabilisation period.
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Record whether the room is open or closed.
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Avoid perfume, alcohol and cleaning spray.
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Record temperature and humidity when available.
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Repeat the measurement at the same time on another day.
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Compare the trend rather than only one number.
Consistency is more important than taking many unrelated readings under different conditions.
When Should You Seek Professional Testing?
Professional testing should be considered when:
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A formal indoor air quality report is required
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Employee exposure must be assessed
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The reading remains elevated over several tests
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Occupants experience persistent irritation or discomfort
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A property dispute involves alleged contamination
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A specific chemical must be identified
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Compliance with a standard or regulation must be demonstrated
The NOYAFA JMS11 and JMS12 are intended for initial screening and comparative checks, not laboratory identification of individual chemicals.
Need Help with NOYAFA JMS11 or JMS12?
MTM Precision supplies the NOYAFA JMS11 and JMS12 air quality testers in Malaysia.
Customers may contact us for:
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Model selection
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Updated specifications
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Basic operating guidance
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JMS11 versus JMS12 comparison
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Alternative PM2.5 or CO2 monitors
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Troubleshooting assistance
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Delivery throughout Malaysia
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Collection from our Puchong showroom
Contact MTM Precision
MTM Precision Sdn. Bhd. (744811-A)
Telephone: +603-8080 7172
WhatsApp: +6016-660 7346
Email: mtmpre@yahoo.com / enquiry@mtmpre.com.my
Website: www.mtmpre.com.my
Showroom & Service Centre:
No. 29-1 & 29-2, Jalan Bandar 18,
Pusat Bandar Puchong,
47160 Puchong, Selangor, Malaysia.
18 Sep 2026
