The ingestion of moisture on the car body and the sensor of the device during a downpour causes instant jumps in readings, which are often mistaken for a putty or a thick layer of paint. The magnetic field used in magnetic-thickness metersIt is distorted due to the dielectric properties of water, and vortex currents in vortex They are affected by a change in the electrical conductivity of the medium, which makes any measurements at the time of direct contact with the liquid incorrect. Experienced specialists in the diagnosis of LCP know that even the thinnest film of water between the probe and the metal can increase the final value by several tens of microns, creating the illusion of repainting where it is not.
The physics of the process dictates its own rigid conditions: water, having a dielectric permeability and electrical conductivity other than air, becomes the third participant in the measurement along with the sensor and coating. If you try to attach sensor To the wet surface, the device will fix the total thickness of paint, water and air microbubbles, which inevitably form under a drop. That is why professionals strongly recommend not to conduct measurements in the open air during precipitation without the use of special protective canopies or at least a simple umbrella that can create a dry pocket above the measured area.
Modern digital devices, such as popular models Coating Thickness GaugeThey are highly sensitive, and raindrops are a serious interference factor. Water can leak into the gaps between the plastic case and the screen, causing short circuits or false buttons, which is especially critical for budget Chinese counterparts without proper sealing. Full immersion or a jet of water under pressure can irrevocably disable the electronics, even if the sensor itself continues to show values.
The principle of operation of sensors and the influence of moisture
Understanding exactly how water affects the outcome requires addressing the physical underpinnings of the equipment. Most of the instruments used to inspect cars are divided into two main types: magnetic (for ferromagnetic metals) and vortex (for non-ferrous metals). In both cases, the presence of an external environment between the measuring platform and the base material makes significant adjustments to the final data.
Magnetic sensors work on the principle of changing the force of attraction of a permanent magnet or magnetic flux depending on the distance to the metal. Water, though weak, is diamagnetic, and its layer creates an additional distance, which the device interprets as an increase in the thickness of the paint coating. If the surface of the vehicle remains waterfilmThe readings can grow by 10-20 microns, which in some cases is a critical error.
- π§οΈ Water creates an additional gap between the sensor and the metal, artificially increasing the thickness.
- β‘ The vortex currents in aluminum bodies change their trajectory due to the conductivity of water, causing chaotic jumps in numbers.
- π Condensation inside the probe can lead to oxidation of contacts and long-term drift of readings.
Particular attention should be paid to vortex devices designed for work on aluminum, copper and brass. The principle of their operation is based on the generation of a high-frequency magnetic field, which leads vortex currents in the conductive base. Water, especially rainwater, which often contains dissolved salts and impurities, has a certain electrical conductivity. This leads to the fact that the device begins to react not only to metal, but also to liquid, giving out completely unreadable values that can change every second.
β οΈ Warning: Never attempt to compensate for the effects of water by software calibration. Attempting to reset the device on a wet surface will lead to the fact that all subsequent measurements will be incorrect, and the real defects of the LCP will remain hidden.
Types of measurement errors in wet weather
Working with a thickness gauge in high humidity or directly during rain is fraught with several types of errors. The first and most obvious is the mechanical obstacle. A drop of water physically does not allow the probe to press tightly to the surface, especially if we are talking about vertical planes where water drains, but leaves a trace. Even a microscopic gap of a few microns filled with water is recorded by electronics as part of the coating.
The second problem is related to the temperature. Rainwater is often colder than the body of a car, especially if the car has just left a warm garage or was in the sun. A sharp temperature drop at the point of contact can cause moisture from the air around the probe to condense, creating the effect of βfoggingβ the sensor from the inside. condensate inside the measuring head is a devious enemy that is difficult to see visually, but which is guaranteed to distort the data.
Technical details of errors
The effects of water and metal temperature can cause thermal EMF in cheap sensors, adding up to 5-10% of the measurement error. In addition, some aluminum alloys, when in contact with water, can oxidize more quickly, changing the surface resistance.
The third aspect is pollution. Rainwater in urban areas is rarely clean. It washes away dust, dirt, oils and chemical agents from the atmosphere. When such a mixture falls under the sensor, it forms an abrasive or sticky substance. Mud porridge can scratch the sensitive surface of the probe, and oily film, washed off the road by rain, will create a stable layer that will interfere with contact for a long time even after the bulk of the water has dried out.
| Type of exposure | Effect on the magnetic sensor | Effect on the vortex sensor | Nature of error |
|---|---|---|---|
| Thin film of water | Overstatement by 5-15 ΞΌm | Unstable value jumps | Systematic |
| Large drop/meadow | The impossibility of tight fit | Total signal distortion | A gross mistake. |
| Dirty rainwater | Risk of scratching and pollution | Change in conductivity of the medium | Chaotic. |
| Condensate on the probe | Corrosion and contact oxidation | Short circuit in the chain | Instrument failure |
Can the device be protected from moisture?
The issue of equipment protection is especially acute when the inspection of the car is necessary urgently, and the weather is not favorable. Tool manufacturers often specify the degree of protection of the housing in the characteristics, denoted by the code. IP (Ingress Protection). For work in the rain, the minimum standard is IP54The first digit means protection from dust and the second digit means protection from water splashes falling in any direction.
However, even having an IP54 or IP65 certificate does not give a carte blanche to work in a rainstorm. These standards imply short-term exposure or mist work, but not direct flow of water under pressure. Moreover, protection primarily concerns the electronics inside the housing, but does not isolate the measuring platform of the sensor, which by definition must be in contact with the object.
Use a silicone case for the case of the appliance if you work in wet weather. It wonβt protect the sensor, but it will save the buttons and connectors from getting moisture, and prevent the wet device from slipping in the hands.
There are specialized long-cabled remote probes that allow you to keep the main unit of the device in a dry place, for example, in a raincoat pocket or under the car canopy. This reduces the risk of water hitting the screen and control buttons. However, the probe itself remains vulnerable. Some craftsmen use homemade solutions, such as transparent film membranes pulled over the sensor, but this method introduces its own, often unpredictable error, requiring recalibration.
- π§ Choose devices with a class of water protection not lower than IP54 for work on the street.
- 𧀠Use rubber gloves so that wet hands do not slip off the body and transfer water to the buttons.
- π§Ό Always have a microfiber on hand to quickly dry the measurement area before each contact.
Practical tips for measuring during rain
If the situation requires the diagnosis of LCD in rainy weather, it is necessary to strictly adhere to the algorithm of actions that minimize risks. First of all, you need to organize at least a temporary shelter. The large diameter umbrella cane is the best friend of the diagnostician in this weather. One person may hold an umbrella, covering a specific area of the body (hood, door, roof) while the second conducts measurements.
It is very important to prepare the surface. Just brushing the water with your hand is not enough, since the thinnest layer of moisture remains. It is necessary to use lilaless napkins or special rags, carefully wiping the place of dryness measurement. After each measurement, the procedure should be repeated, as new rain or condensation can come on instantly. The speed of work at the same time drops by several times, which should be taken into account when planning the inspection time.
βοΈ Checklist for work in the rain
Do not forget about personal safety and comfort, which directly affect the quality of work. Trembling with cold or wet hands are not able to provide a stable pressing of the sensor. Uneven pressing force is another common cause of errors. Therefore, working in the rain requires more frequent breaks for warming and drying hands, as well as the use of quality waterproof clothing.
β οΈ Warning: If water gets inside the housing through a cable connector or battery compartment, immediately remove the power cells and place the appliance in a container of silica gel or rice. Do not try to turn on the device until it is completely dry!
Comparison of readings: dry and wet surface
To understand the scale of the problem, consider a hypothetical experiment. Take a car with a factory paint thickness of 110 microns. When measured on a dry, clean surface, the instrument will show a value in the range of 105-115 ΞΌm, which is the norm. If moisture remains on the surface after rain, the readings can jump to 130-140 microns. For an inexperienced buyer, this can be a signal that the part has been repainted, when in fact it is just a water effect.
With aluminum parts, the situation is even more dramatic. The vortex method is more sensitive to changes in the dielectric permeability of the gap. Wet aluminum can show a range of values from 80 to 200 microns on the same patch of several millimeters, simply because the surface microrelief holds water unevenly. Such βjumpingβ numbers are often interpreted as the presence of a putty, which is an erroneous conclusion.
The difference in indications between dry and wet surfaces can reach 30-50% of the actual thickness of the coating, which makes diagnosis in the rain without drying meaningless.
It is also important to note the effect of temperature. Wet metal cools faster due to evaporation of moisture. Cold metal can have slightly different magnetic properties (although for steel this effect is minimal in the household range), but the main thing is that a cold sensor in a warm hand or vice versa creates conditions for condensation. Therefore, comparing the readings βbeforeβ and βafterβ the rain on the same machine without intermediate drying in a warm box will not give an objective picture.
FAQ: Frequently Asked Questions
Can a full waterproof thickness gauge measure the thickness under water?
No, even if the device has a high degree of protection of the housing (for example, IP67 or IP68), this means only its ability to survive the dive, but not work. The measurement principle requires solid-body contact (LCP) of the sensor, and water is the medium that distorts the signal. Measurement of the water is not physically correct.
How much does rain understate or overstate the reading?
In the vast majority of cases, the presence of water overstate indications, since the device summarizes the thickness of the paint and the thickness of the water film. Understatement is almost impossible unless water causes a short circuit in the sensor circuit, resulting in zero or erroneous values (Error).
What to do if the thickness of the wet?
It is necessary to immediately turn off the device, remove the batteries and thoroughly wipe the body with dry rags. Do not use a hot air dryer to avoid melting the plastic or screen. Leave the device to dry in a warm dry place for at least 24 hours before the next turn on.
Does air humidity affect the operation of the device?
High humidity in the air does not affect the magnetic properties of steel or aluminum. However, it contributes to the formation of condensation on the cold parts of the body and on the device itself, if it was introduced from the cold into the heat. Condensation, not humidity, is the enemy of precision.