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Monitoring the Process Parameter Surface Tension

Reliable Process Tensiometer:

- Continuous measurement of the surface tension of process liquids
- Monitoring and controlling the surfactant/wetting agent concentration
- Automatically working plant unit


- Quality assurance and documentation of the process development
- automatic dosing of surface active agents according to the consumption
- highest product quality through controlled process management
- process solution for high process reliability
- less cleaning agent consumption, environmental protection, cost reduction through process optimization


SITA clean line ST brochure

Product description

The Process Tensiometer SITA clean line ST continually and automatically measures the surface tension of process fluids used in the parts cleaning industry, surface technology, semiconductor and photovoltaic industry, as well as the chemical industry.


The process parameter surface tension, and thus the concentration of surface-active agents like surfactants, wetting agents and solvents, are measured and documented inline. Connected to the plant control, the SITA clean line ST measuring system carries out an automatic dosing of active agents according to the consumption.


The Process Tensiometer SITA clean line ST works fully automated, including:
- handling of process liquid,
- self cleaning function,
- calibration of surface tension senor and
- self diagnostic including error indication and logging.

The process liquid sample is either lead back into the process again or rejected. No further equipment is necessary except of a tap water supply.


Used with an industrial PC or an SPS with touch panel, the central control unit of the SITA clean line CC allows process-specific system solutions to be realized.


SITA application engineers develop an optimal and customized SITA clean line system solution based on an analysis of your process and plant.

Measuring principle

Like all SITA Tensiometers, the SITA clean line ST process measuring device is based on the bubble pressure method to measure the dynamic surface tension in liquids. Therefore, as it can be seen on the picture, an air stream is lead into the sample liquid through a robust capillary and the pressure development necessary for the bubble generation is measured. (more information …)


Continual monitoring and dosage according to the consumption:

- Cleaning agent component surfactant in baths of industrial parts cleaning of companies operating in the field of mechanical engineering, automobile industry, electrical engineering and microelectronics
- IPA-Concentration in texturing baths for silicon-wafers of photovoltaic industry

Wetting agent concentration of developer solutions for lithography processes of the semiconductor industry

Practical example: automatic cleaning agent dosing before coating automotive pistons

High cleanliness standards of automotive piston surfaces before coating with an anti-friction-layer require a management of the cleaning agent concentration within pre-determined limit values.


The system solution SITA clean line ST continually monitors the cleaning agent components and ensures their dosage according to the consumption. Thus, a depletion or an overdose of cleaning agent can be avoided guaranteeing an optimal cleaning quality. The process reliability can be sustainably increased as well as the efficiency through to a reduction of cleaning agent.

Here you can find further application examples [..]

Technical data

Surface tension
Measuring Range 10...100 mN/m (dyn/cm)
Resolution 0,1 mN/m (dyn/cm)
Bubble lifetime
Control Range 15...15.000 ms
Resolution 1 ms
Sample temperature
Measuring Range 0...80 °C
Resolution 0,1 K
General data
Dimensions (W x H x D) and Housing 480 mm x 480 mm x 170 mm (HxBxT), Stainless steel (1,430l)
Weight ca. 23 kg
Acceptable Surrounding Temperature 10...40 °C
Liquid tangent materials
Metal vessel type Stainless steel (V2A & V4A), PTFE, FKM (viton), PEEK, PU, PA
Glass vessel type Stainless steel (1,4401, 1,4408, 1,457l), borosilicate glass, PTFE, FKM (viton), PEEK

Operational Voltage 110 … 240 V, 50 … 60 Hz, maximum 350 W
Serial Interface (Service) RS323, 9 pin SUB-D
Remote Maintenance Modem, analogue
Signals Error / Interruption, exceeding
Measurement request Access for isolated contact

Current Interfaces

Surface tension 0...100 mN/m: 4...20 mA
Temperature 0...100 °C: 4...20 mA
Fluidic connections
Water supply 2 … 6 bar, G ¼” inner span (10… 80° C)
Sample supply 1 … 6 bar, G ¼” inner span (10 … 80° C)
Water & Sample drain

Tube fitting


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A business unit of SITA Messtechnik GmbH.

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