FAQ

Between series of measurements (or overnight or over the weekend) you can place a beaker of water under the instrument instead of the sample In this way, the Capillary and temperature probe remain submerged. This ensures that no contamination or sample residue dries out and the plastic of the capillary remains moist and easily wettable.

If the device is not used for a longer period of time (longer than a weekend), clean the capillary and place it in the device case.

Before use, we recommend placing new capillaries or capillary not used for a long period of time in a beaker of deionised water, so that the plastic becomes moist again.

After a measurement, clean the capillaries externally with water only, for example using a spray bottle. It is not necessary to remove the capillary from the device for cleaning. Please do not immerse the capillary completely. Water inside the capillary can lead to incorrect measurements and takes time to dry. Avoid touching the capillary tip as it is sensitive to mechanical damage.

The measured Surface tension is temperature-dependent. As the temperature increases, the surface tension decreases (exception: cloud point in non-ionic Surfactants). 

Additionally, the solubility of some sample components, such as boric acid, is also temperature-dependent. This must be considered to avoid crystallization at the capillary tip.

Some contaminants, such as cooling lubricants, contain surfactants themselves, which can affect the measured surface tension.

The viscosity of the liquid acts as an additional force against the formation of air bubbles and increases the measured pressure signals. The impact is greatest at high flow rates (short bubble lifetimes) and decreases with increasing Bubble lifetime. Measurement of dynamic surface tension is generally possible up to approximately 2000 mPa*s (with a limited dynamic range).

The surface tension is temperature-dependent. The sample temperature for subsequent product or process control should match the temperature at which the reference values were recorded. A tolerance of ±3 K is often acceptable, but it is best to check the dependence. We recommend conducting measurements at room temperature.

For non-ionic surfactants, it is important to measure the samples below the cloud point temperature.

A measurement always takes slightly longer than the specified bubble lifetime. Initially, the Tensiometer automatically adjusts the flow rate until the bubble lifetime is reached. Then, if set, measurement values are discarded, and individual values are collected for the averaged result (the individual values are displayed but not saved).

A quick single measurement with the SITA DynoTester+ takes only a few seconds to several minutes, depending on the maximum bubble lifetime and the averaging settings.

Auto-scans with the SITA pro line t15+ or the SITA science line t100 can take several minutes to up to an hour, depending on the parameters settings.

The duration of continuous online measurements with the SITA pro line t15+ or the SITA science line t100 can be freely chosen.

SITA bubble pressure tensiometer don't depend on the immersion depth. Therefore, the handeling is very uncomplicated. Also, the density of the liquid being measured (often unknown) does not have to be determined and entered prior to measuring.

No, free-hand measurements lead to inaccurate readings due to inevitable movements, especially at higher bubble lifetimes. Always use the stand for measurements.

The capillaries used are permanent capillaries made of PEEK (polyetheretherketone) and glass, the disposable capillaries made of PTFE (polytetrafluoroethylene, 'Teflon').

The PEEK type I capillary is used as a laboratory standard for relatively homogeneous surfactant solutions, dyes and inks without particulate contamination. 

The PEEK type II capillary is used as a process standard, particularly for solutions contaminated with particles or emulsions. This capillary is designed for continuous use.

PEEK has high thermal resistance and good resistance to the effects of highly concentrated alkalis, non-oxidising acids and many solvents, as well as excellent hydrolysis resistance to boiling water. However, the capillaries have low resistance to concentrated sulphuric acid and oxidising media such as concentrated nitric acid or wet chlorine gas. Although PEEK is a very dimensionally stable plastic, mechanical stress on the capillary tip should be avoided.

For special applications, glass capillaries (e.g. sulphuric acid or chromosulphuric acid solutions) and disposable PTFE capillaries (e.g. adhesives, coatings) are used.

Ensure that the samples are representative by mixing them or taking samples from a well-mixed area. In some cases, (e.g. galvanic applications) the liquid volume should first be brought to application temperature to bring all components into solution.

Surface tension is temperature dependent. Bring and maintain the samples at the desired temperature (tempering or insulation).

Mix the samples prior to measurement, e.g. with a magnetic stirrer or manually, to ensure ho-mogeneous distribution of all components. The liquid has to rest before measurement, as the movement of the liquid affects the small air bubble at the tip of the capillary.

A measuring system analysis must always take into account the photo bleaching effect as well as the uneven distribution of contamination on a surface. 

In a first step, we therefore recommend conducting the measurement system analysis with the SITA Calibration Standards; where these effects do not occur. 

Further measuring system analyses that also examine the influences of the tester and the test specimen, should consider the influence of uneven distribution of the contamination as well as the photo bleaching effect.

Processing aids such as oils, greases, cooling lubricants and release agents are technical liquids that also contain numerous additives, which can likewise contribute to Fluorescence. 

Whether a contamination fluoresces sufficiently depends on the particular application and can be assessed by a simple fluorescence test. Whether a contamination can be detected in the quantities that are disruptive for your process, can easily be determined based on parts from your process. This should be checked with uncleaned as well as with well cleaned and poorly cleaned parts.

The SITA CleanoSpector is designed as a hand-held measuring device. The fluorescence measurement technology SITA clean line CI is used for inline measurements or for scanning surfaces. Due to the adjustment with the SITA Calibration Standards, the measuring results (RFU value) of all hand-held measuring devices SITA CleanoSpector are comparable to each other as well as to the inline sensors SITA clean line CI (if the same optic version is used).

We recommend a regular inspection with the included Calibration Standards. In the default setting, the SITA CleanoSpector issues the warning “Check required” 40 days after the last check. In addition, as part of your regular monitoring of measuring equipment, we recommend servicing and adjustment of the SITA CleanoSpector and the corresponding Calibration Standards by SITA every 1-2 years.

The base material can influence the measurement. One influencing factor is the basic fluorescence of the part material. Metal and ceramic surfaces do not fluoresce. In the case of glass surfaces, fluorescence is possible due to contamination in the amorphous structure. Other materials such as paper, textiles and plastics tend to fluoresce more strongly due to their complex structure of organic molecules. In the case of fluorescent base materials, it must be determined whether a reliable Cleanliness inspection of these parts with a fluorescence measurement is possible.

Another influencing factor is the property of the basic material to absorb or reflect light in different Wavelength ranges. The same coating thickness of a particular material can provide different RFU values on copper and on stainless steel. In practice, however, this is of secondary importance, since limit values for sufficient cleanliness of parts should always be defined for the specific process. In addition to the quantity of contamination, the limit value is affected by the type of contamination, the follow-up process, and the influence of the basic material on the follow-up process

The surface Roughness has only a secondary influence on the measurement, because the meas-urement does not detect the reflected UV radiation, but rather the emitted fluorescence of the contamination. As a point light source the fluorescent light radiates in all directions. However, the surface roughness does influence the cleanliness of the part itself, because rough surfaces are generally harder to clean.

No, the sensor head does not necessarily have to be perpendicular to the surface. Deviations of ±15° around the perpendicular will not cause significant changes of the measured Fluorescence intensity. Depending on the application, higher angles are also permissible. If the angle of the measurement is always the same, such as 45°, the measured values are comparable with each other (45° with 45°), not however with measured values of 0°.

Filmic contaminations are generally distributed unevenly on the surface. They are dependent on the geometry of the part, as well as the machining and cleaning process. Typically, heavier contamination is distributed more unevenly. The cleaner the surface, the lower the RFU values and also the divergence of the measuring values.

This is due to the photo bleaching effect. Photo bleaching is a dynamic process in which the contamination is photo-chemically destroyed by the UV excitation, which reduces its ability to fluoresce. The intensity of the photo bleaching effect depends on the material. 

In practice, the photo bleaching effect is of secondary importance in the cleanliness inspection of parts. A multiple measurement of the same spot is not practical. Instead, one should measure on several different spots in order to obtain an average, which then makes it possible to assess the cleanliness of the part. 

We recommend conducting a measuring system analysis with multiple measurements using the SITA Calibration Standards to eliminate adverse effects from photo bleaching and positioning.

The optimal measuring distance is decisive for a correct measurement. You can easily set the measuring distance by placing the sensor with a spacer on the part or by measuring with a stand and target pointer. Deviations from the optimal measuring distance result in lower measured RFU values. The influence of the distance depends on the optic version of the sensor.

The SITA CleanoSpector automatically compensates for the ambient light by measuring both the ambient light and the radiation emitted by the fluorescence. Excessive ambient light can result in an overload of the detector diode (Warning on device "Ambient light!"). Fast changes in the light conditions, for example by switching on ceiling lights or fluctuating shade during a measurement can cause measurement deviations. Fast changes in light during a measurement should therefore be avoided.

If the SITA CleanoSpector detects a change in the ambient light it will output the warning “Ambient light fluctuation”. In this case, it is recommended that you improve the measuring conditions or ambient light conditions (steady light conditions or shading) and repeat the measurement.

When performing a measurement system analysis, the Photobleaching effect and the uneven distribution of contamination or sample separation must be taken into account. 

It is therefore recommended to carry out the measurement system analysis in the first step on the SITA fluorescence standards, as these effects do not occur there. 

For further measurement system analyses, in which the influences of the tester and test specimen, should consider the influence of uneven distribution of the contamination as well as the photo bleaching effect.

In production aids, fluorescence is largely due to the aromatic ring systems contained as additives and the unsaturated structures of the oils and fats. Carboxylic acids and their esters as well as aliphatic ketones also fluoresce. With fluorescence measurement, the smallest amounts of fluores-cent substances can be detected. 

Processing aids such as oils, greases, cooling lubricants and separating agents are technical liquids which, in addition to the basic substances, also have a large number of additives which can also contribute to fluorescence. 

The SITA ConSpector is designed as a hand-held measuring device. The SITA clean line BC is used for fully automatic bath control.

Regular testing as a blank measurement is recommended. In addition, a reminder after a maximum time interval between two checks can be set in the device. 

In the default setting, the SITA ConSpector issues a warning "Test required" 40 days after the last test. This is not a generally valid recommendation, but should be shortened or extended depending on the frequency of use, the operating environment and the requirements of the measuring task. 

In addition, it is recommended to have the SITA ConSpector and the optionally associated standards serviced and adjusted by SITA every 1 - 2 years as part of the monitoring of the measuring equipment.

The SITA ConSpector automatically compensates for the ambient light by measuring both the ambient light and the radiation emitted by the fluorescence. Excessive ambient light can result in an overload of the detector diode:Warning on device “Ambient light!”. Fast changes in the light conditions, for example by switching on ceiling lights or fluctuating shade during a measurement can cause measurement deviations. 

Fast changes in light during a measurement should therefore be avoided. Therefore, it is recommended to measure in a stainless steel beaker with a closed lid. If the SITA ConSpector detects changes in ambient light, it issues the warning "Ambient light fluctuates". In this case it is recommended to improve the measuring conditions/ambient light conditions (measurement in a stainless steel beaker with closed lid) and to repeat the measurement.

Using the rinse function, rinse the water-carrying hose system to remove any trapped air bubbles (Be careful, a continuous stream of water is produced!). If no water comes out even after repeated rinsing, check whether the rubber seal under the sensor cover closes tightly. Otherwise, please contact our SITA support.

Pay attention to the correct sequence of steps in the Checking or Adjustment procedure. When starting the procedure, the sensor starts to initialize, then use the zero standard (without bead) and the bead standard. If the standards are not used according to the on-screen text, the test will fail or the unit will be incorrectly adjusted. You can reset the unit to the factory calibration at any time.

After extended periods of disuse, even with ultrapure water, residues of water droplets may become visible on the material surface after drying. These residues form when the ultrapure water remains in contact with the storage container for a long time. In this case, emptying the storage container (using the flushing function) can help. Afterwards, refill the system with degassed ultrapure water.

Dyne inks are used to check the Wettability of a surface. As result, the spreading liquid’s surface tension is noted as wettability value. Due to different ink formulations or residues on the surface, surface tension (of the liquid) typically tends not to be equal to surface free energy (of the solid). Correlations between the dyne ink’s surface tension value and the measured Contact angle only apply to those application cases the correlations were made for.

The measurement on inclined surfaces and even overhead is possible. Due to the small microliter-sized drop, the effect of gravitation force on the drop is minimised. For optimal comparability, retain the measuring arrangement during the measurements.

The surface roughness intensifies the measured contact angle in both hydrophilic and hydrophobic direction by strengthening the Wetting behaviour. 

On wettable hydrophilic surfaces with contact angles <90°, the increasing roughness enhances the hydrophilicity, measurable in lower contact angles. In the other direction, on hydrophobic surfaces with contact angles >90° a higher roughness increases the contact angle by enhancing the hydrophobicity. 

The camera views the shadow of the droplet on the inclined projection surface from the top. The position and inclination of the projection surface is fixed, the edge of the surface corresponds to the baseline. After changing the projection surface, the adjustment procedure sets the base line values.

The device uses intense red light for the droplet illumination which provides a high-contrast image. In general, common ambient light can be neglected. Nevertheless, it can occur in individual cases (e.g. spotlight) that shadowing is necessary.

The SITA FoamTester can be used to make liquids Foam and test them, e.g. liquid cleaning chemicals, cosmetics, or cooling lubricants. Liquid paints, colours, and inks are also typical test objects.

Hard foams such as foam concrete or metal foams cannot be measured.

The automatable measuring system allows for reproducible repeat measurements from a larger overall volume without user intervention. To do this, prepare an appropriate volume of the test solution and place it in the sample reservoir of the SITA FoamTester.

Alternatively, connect the SITA FoamTester via software to a dosing unit to increase the concentration or add additional liquids during the automated experiment.

The amount of filled volume should be adjusted to the foamability to prevent overfoaming. Typical volumes are 100-300 ml.

The duration of an experiment is largely determined by the number of stirring cycles and the foam stability. Unstable foams decompose quickly, while stable foams take several hours to decompose. Therefore, a time limit is often set for observing the Foam decay.

The SITA FoamTester is connected to a fresh water supply and has an automatic cleaning function with water. Additionally, the measuring vessel can be removed and cleaned by hand or in a laboratory dishwasher. For this purpose, the stirring disc can be removed from the glass vessel.

However, any scratches and damages must be avoided by all means, as they can have a significant impact on the optical measurement and make the glass fragile at these points.

The foam formation of a liquid is influenced by the temperature during the experiment as well as the hardness of the used water. For comparable experiments, temperature, water hardness and sample volume should therefore be defined and consistent. Contaminants such as defoamers from a previous experiment affect foam formation as well.

Furthermore, the optical measurement system can be influenced by contamination of the vessel wall.

The measured result can also be affected by the timing of the experiment. A large Foam volume needs time to settle, while for weakly foaming products, the interval between foam generation and volume determination should be as short as possible.

An optional, external thermostat regulates the temperature of the sample volume in the sample reservoir of the SITA FoamTester. The temperature during the measurement may range between 0 and 60°C.

The measurement with the SITA FoamTester is not standardised. Although there are standardised procedures such as the Ross-Miles test (ASTM D1173), but its quantitative statement is limited to the maximum foam volume and the observation of foam decay. Additionally, it differs in the method of foam generation and is restricted to highly foaming solutions.

Other quasi-standardised tests, such as the plate test for determining the performance of a dishwashing detergent, specifically address the needs of a particular industry.

For comparability with the SITA FoamTester, Triton X100 is used as a surfactant standard, but SDS or SLES are also suitable surfactants.

While the SITA FoamTester determines all foam properties optically, the R-2000 used a conductivity needle sensor. As a result, the R-2000 worked significantly slower and had disadvantages in measuring quickly decaying foams. In addition, the measuring principle was only suitable for conductive liquids.

With its fast optical measurement methods, the SITA FoamTester determines additional foam properties such as different volume types, Drainage behaviour, and Foam structure.

The principle of mechanical foam generation with the proven stirring disc remains the same. This ensures that the generated foams are comparable.