Level Measurement of Silica Gel in Raw Material Storage Drums

Responsible for manufacturing the intelligent inner ‘brains’ of each of VEGA’s products, VEGA’s electronics manufacturing department is situated in Schiltach. Over a million printed circuit boards are produced there each year, for sensors and signal conditioning instruments.

They are potted and sealed with a special 2-component silicone gel, in order to ensure a long service life in the face of inhospitable operating conditions.

VEGAPULS 64 Radar Sensor

However, which level measurement technology is used to ensure the continuous operation of the potting machine in the raw material storage drums? This is the ideal application for the VEGAPULS 64 radar sensor equipped with 80 GHz technology.

Silicone gel storage drums with VEGAPULS 64 radar sensors.

Silicone gel storage drums with VEGAPULS 64 radar sensors.

The head of VEGA’s electronics manufacturing department, Marcel Schrempp, is particularly happy with these compact radar sensors. After all, they are extraordinarily reliable at measuring the level inside two 200 liter storage drums. Inside these drums are the liquid components of the potting compound which is illustriously named 'Sylgard® 527', made by Dow Corning.

Sylgard 527 belongs to a group of products which are extremely difficult to measure using radar technology as they are electrically non-conductive and have a low dielectric constant measuring 2.85.

However, these are precisely the properties which are needed in order to guarantee that the hardened potting compound which is injected into the electronics module can protect the highly integrated electronics from voltage flashovers, moisture, and leakage currents.

Sensors with Smartphone Apps and Bluetooth Capabilities

The sensors, which have a small ¾" threaded fitting, measure through a narrow adapter which fits down into the barrel in daily operation. At present, VEGAPULS 64 is the only product on the market which offers this special focusing and size, courtesy of its high transmission frequency of 80 GHz. At the potting machine’s control panel, the measured value is visualized. This informs the operator when they ought to schedule a drum change.

It goes without saying that this is also possible using smartphone apps and the new Bluetooth capabilities of the sensors.

The current filling levels of the intermediate containers and storage drums are shown by the machine’s screen.

The current filling levels of the intermediate containers and storage drums are shown by the machine’s screen.

It is very straightforward to exchange the drum. Simply lift the sensor out of the adapter, unscrew the adapter from the drum, and then use plugs to close the empty drums. Following this, place two new, full drums at the dispensing point, before refitting the adapter and sensor.

The days when capacitive probes were used to measure the level are long gone. While this was an effective solution in terms measurement technology, it required the probes to be initially disconnected electrically every time the drum was exchanged, before being unscrewed and pulled out of the drum in their complete length.

Comparatively, this was a significant amount of potentially messy work, as the silicone compound would drip from the probe during the change-over.

Intermediate tank with two capacitive measuring points with VEGACAL 63.

Intermediate tank with two capacitive measuring points with VEGACAL 63.

In terms of the process, a key concern is how the silicone gel gets from the drums to the electronics cups. This is achieved with the use of a vacuum pump, which sucks exactly the amount needed from the storage drums in order to fill two smaller intermediate containers on the potting machine. Each of these containers has an approximate capacity of 36 liters.

Filling station with the two static mixers in the middle of the picture. The pressure is measured by four VEGABAR 17 sensors.

Filling station with the two static mixers in the middle of the picture. The pressure is measured by four VEGABAR 17 sensors.

VEGACAL 63 Capacitive Measuring Probes

Built-in VEGACAL 63 capacitive measuring probes are also used for the level monitoring of these containers. The extraction from these containers is facilitated by two eccentric screw pumps, which build up the required pressure of approximately 3.5 bar which is needed for filling.

The material travels through a static mixer before going into the electronics cup via the filling nozzles. The static mixer is just a piece of pipe with a fixed spiral. Both components are pressed and mixed together through this. The quantity required flows into the respective electronics in between 30 and 60 seconds.

Approximately 100 liters of silicone run through this system on a typical working day. Consequently, drums must be exchanged roughly once every four days, and approximately 250,000 electronics modules are filled by the machine each year. The gel hardens just a few hours after mixing, achieving the level of firmness desired. This is precisely the property which protects the sensor electronics against vibration in rough daily use.

Conclusion

As this example indicates, even level measuring operations at this factory have been solved and optimized satisfactorily. There are also a number of other new possibilities opening up, such as those offered by over 10,000 customer applications from those using VEGAPULS 64.

This information has been sourced, reviewed and adapted from materials provided by VEGA Grieshaber KG.

For more information on this source, please visit VEGA Grieshaber KG.

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