Why Does My Wintact WT-100A Ultrasonic Thickness Gauge Reading Fluctuate? Malaysia
Why Does My Wintact WT-100A Ultrasonic Thickness Gauge Reading Fluctuate? Malaysia
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A common question when using an ultrasonic thickness gauge is:
“Why does the thickness reading keep changing even when I measure the same location?”
If your Wintact WT-100A Ultrasonic Thickness Gauge gives unstable or fluctuating readings, it does not necessarily mean the instrument is faulty.
Ultrasonic measurement depends on several factors, including surface condition, ultrasonic coupling, probe contact, material properties, sound velocity and operator technique.
Understanding these factors can help maintenance technicians, engineers and QA/QC personnel obtain more consistent thickness measurements.
1. Insufficient Ultrasonic Couplant
One of the first things to check is the couplant.
The probe needs good acoustic contact with the test material. Air gaps between the probe and surface can interfere with ultrasonic transmission.
If the reading is unstable:
Apply suitable couplant
Make sure the probe face has good contact
Reposition the probe
Repeat the measurement
Do not assume that pressing the probe harder will always solve the problem.
2. Rough or Corroded Surface
Heavy corrosion can make ultrasonic thickness measurement more difficult.
A surface may contain:
Rust
Scale
Pitting
Dirt
Uneven areas
Loose material
These conditions can reduce probe contact and cause readings to vary.
Where appropriate, prepare the measurement area according to the inspection procedure before taking the final reading.
3. Wrong Material Sound Velocity
This is another important source of measurement error.
Ultrasonic thickness is calculated using the sound velocity of the material.
If the instrument is configured for the wrong material, the displayed thickness may be incorrect.
For example:
Steel ≠ Aluminium ≠ Copper ≠ Plastic
Different materials require appropriate sound-velocity settings.
A stable reading can still be wrong if the material setting is incorrect.
4. Probe Position Is Changing
Probe movement can affect the ultrasonic signal.
Try to keep the probe:
Stable
Properly coupled
Correctly positioned
Consistently oriented
This becomes particularly important when measuring small components or curved surfaces.
5. Measuring Small-Diameter Pipes
Curved surfaces can be more difficult than flat steel plates because the probe may not sit evenly on the surface.
When checking pipes:
Ensure good probe contact
Use sufficient couplant
Take several readings
Follow the appropriate probe orientation and procedure
Do not rely on one unstable reading.
6. Paint or Coating on the Surface
A painted surface can influence ultrasonic thickness measurements.
The ultrasonic signal may travel through both the coating and base material depending on the instrument and measurement method.
If accurate remaining metal thickness is required, confirm whether the instrument and procedure are suitable for measurement over the coating.
Do not automatically assume that a conventional reading excludes the paint thickness.
7. Heavy Pitting
Corrosion is not always uniform.
Consider a pipe with a generally acceptable wall but one localised deep pit.
Moving the probe only a short distance may produce different readings because the actual remaining material thickness changes across the surface.
For example:
Point A: 7.62 mm
Point B: 7.55 mm
Point C: 6.81 mm
Point D: 7.59 mm
Point C should not simply be dismissed as a bad reading.
Repeat the measurement and investigate the surrounding area.
8. Material Is Difficult for Ultrasonic Measurement
Not every solid material transmits ultrasonic energy equally well.
Factors such as:
Coarse material structure
Internal porosity
Laminations
Composite construction
Irregular geometry
can affect ultrasonic signals.
If the application involves an unusual material, confirm suitability before relying on the measurement.
What Should You Do When the Reading Is Unstable?
Use this simple troubleshooting sequence:
Check Surface → Check Couplant → Check Material Setting → Check Probe Contact → Repeat Measurement
Then take several readings around the same location.
For example:
7.51 mm → 7.50 mm → 7.52 mm
is much more convincing than:
7.51 mm → 8.63 mm → 6.72 mm
Large variations should be investigated before recording a final value.
Don't Record Only the Lowest Number
Another common mistake is automatically recording the lowest reading displayed.
Instead, determine whether the reading is:
Repeatable
Obtained with proper coupling
Taken at the intended location
Consistent with the measurement procedure
If a genuinely repeatable low-thickness area is found, document the exact location and investigate further.
Create Better Thickness Inspection Records
For corrosion monitoring, record more than just the thickness.
A useful record might include:
Equipment: Pipe P-203
Location: Elbow
TML: 04
Reading: 6.82 mm
Surface Condition: Corroded
Date: Inspection Date
Remarks: Repeated measurement confirmed
This allows the same location to be checked during the next inspection.
Is the WT-100A Faulty If Readings Keep Changing?
Not necessarily.
Before concluding that an ultrasonic thickness gauge has a problem, check:
Probe condition
Couplant
Test surface
Material setting
Measurement technique
Reference material of known thickness
If the instrument cannot produce repeatable results on a suitable reference sample under correct conditions, further checking may then be appropriate.
Looking for an Ultrasonic Thickness Gauge in Malaysia?
MTM Precision supplies ultrasonic thickness gauges and industrial testing instruments for Malaysian engineering, manufacturing, maintenance and inspection applications.
If you are experiencing difficulty selecting or using a thickness gauge, provide us with:
Material → Approximate Thickness → Component → Surface Condition → Application
This information can help determine which ultrasonic thickness measurement solution is suitable.
Contact MTM Precision
MTM Precision Sdn. Bhd.
Showroom & Service Centre
No. 29-1 & 29-2, Jalan Bandar 18,
Pusat Bandar Puchong,
47160 Puchong, Selangor, Malaysia
🌐 Website: www.mtmpre.com.my
📧 Email: mtmpre@yahoo.com
📱 WhatsApp: +6016-660 7346
10 Aug 2026
