VapoMeter FAQ

What is the operating principle of the VapoMeter?
How do I know that the VapoMeter is ready for next measurement?
How long is the measurement time with the VapoMeter?
How does the VapoMeter differ from other TEWL meters?
What is the accuracy of the VapoMeter?
What is the possible measuring range?
How is the VapoMeter calibrated?
How does the angle of the VapoMeter with respect to the measurement site affect the measurement?
What is the difference between the standard and the small (nail) adapter?
How do I clean and sterilize the VapoMeter?

What is the operating principle of the VapoMeter?

The VapoMeter is equipped with a closed cylindrical chamber that contains sensors for relative humidity and temperature. When the VapoMeter is in contact with the skin or other measured surface,the relative humidity (RH%) in the chamber begins to increase. The TEWL value is calculated from the information the instrument acquires based on this increase.

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How do I know that the VapoMeter is ready for next measurement?

The ventilation time of the chamber between measurements is automatically controlled. Relative humidity in the chamber has to decrease back to ambient RH level, before the VapoMeter is ready for next measurement. The ventilation period is longer after high values (after 10 g/m²h about 10 seconds and after 100 g/m²h about 60 seconds). The message "Press to measure" appears on the display after the ventilation period indicating that the VapoMeter is ready for the start of the next measurement.

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How long is the measurement time with the VapoMeter?

A measurement with the VapoMeter takes 5 to 16 seconds with the standard adapter and 9 to 32 seconds with the nail adapter. The measurement time is automatically controlled and the progress bar is shown on the display; the higher the TEWL, the shorter the measurement time. At the level of 10 g/m²h the measurement time is 10 seconds with the standard adapter and 20 seconds with the nail adapter. Under the level 1 g/m²h with the standard adapter and 2 g/m²h with the nail adapter the measurement time is 16 and 32 seconds respectively.

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How does the VapoMeter differ from other TEWL meters?

The measurement principle of the VapoMeter differs completely from the conventional devices in the market. It is a closed chamber system that calculates the evaporation rate from the increase of relative humidity in the measurement chamber. Compared with the open chamber technique, the measurement time is shorter, the device is smaller and portable and ambient air flows do not disturb the measurement. Continuous measurements are not possible, but since a single measurement period is short, up to 2 measurements per minute at low evaporation rates are possible.

The VapoMeter also differs significantly from the Aquaflux closed chamber device. The VapoMeter does not create any artificial micro-climate in the chamber and thus it does not change the skin's normal evaporation rate. The VapoMeter does not need daily set-up or calibration procedures nor any de-icing process as do the other devices.

The VapoMeter is the only TEWL instrument in the market that is fully portable and that can be used in field conditions. Also, the VapoMeter is the only one with wireless data transfer.

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What is the accuracy of the VapoMeter?

Accuracy in measuring evaporation rate through a semipermeable membrane is ± 4 %. This is tested against gravimetric evaporation rate (mass change of water samples covered with vapour permeable membrane). The coefficient variation (CV) measured on the skin is typically less than 5%.

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What is the possible measuring range?

The recommended measurement range is from 3 to 200 g/m²h, but the VapoMeter can measure evaporation rates beyond these values. With the nail adapter values up to 300 g/m²h can be measured. As the VapoMeter is based on the closed chamber principle, it is accurate in these high values. Conventional open chamber devices begin to underestimate TEWL values already at 50 g/m²h.

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How is the VapoMeter calibrated?

The VapoMeter is factory calibrated. Each calibration holds for up to 2 years unless the VapoMeter is used in very variable conditions or on a daily basis continuously. We recommend recalibration every other year or once a year for units in heavy use. Please contact your local representative if you need to recalibrate your VapoMeter.

The calibration service is performed in specific conditions at the manufacturing plant. Evaporation rates through semipermeable membranes are measured at 3 different levels and at different RH conditions. The water loss is calculated from the mass change of the water sample and your VapoMeter is programmed accordingly.

This ASTM based calibration method has been in use for many years and the achieved evaporation rates represent skin evaporation rates very well. This is not the case with so-called droplet calibration methods where water drop evaporation is speeded up during the calibration. These methods do not reflect the skin barrier's natural evaporation speed.

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How does the angle of the VapoMeter with respect to the measurement site affect the measurement?

During the measurement the measured skin area has to be sealed by the adapter. Apart from this the VapoMeter is orientation independent and the angle of use does not affect the measurement values. This is due to the closed chamber and the measurement principle.

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What is the difference between the standard and the small (nail) adapter?

The standard adapter has on opening diameter of 11 mm and it is designed for use on normal skin sites. The standard adapter can be used for values up to 200 g/m²h. The small adapter's opening diameter is 4,5 mm and it is fitted with a silicone ring. It can be used for hard surfaces like the nail or for other small difficult areas like the lip, eyelid, armpit, etc. It is also recommended to use the nail adapter when measuring very high evaporation rates, up to 300 g/m²h.

It is necessary to change the measurement mode of the VapoMeter when changing between the standard and the small adapters. When using a small adapter the VapoMeter display must show "Small" on the top of the display during the measurement.

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How do I clean and sterilize the VapoMeter?

The VapoMeter may be wiped clean with a soft and moist cloth, if necessary. Care should be taken not to touch the sensors in the chamber. The adapters that are in contact with skin can be sterilized separately by autoclave or ethanol.

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