FUNDAMIX® Amplitude Monitoring

 

The FUNDAMIX® is a well established mixing technology for products which require mixing at low shear forces, which is typically the case in the biotech environment. While cGMP practices intend to control production processes to guarantee quality of products, it means that the mixing quality of an agitated vessel needs to be monitored to assure compliance.

Vibratory action on a mixing plate produces a vertical flow of the fluid. The displacement volume is basically a function of frequency x amplitude. When the drive unit is connected straight to the power supply the oscillating frequency is equal to twice the grid frequency, i.e. either 2x50Hz = 100Hz or 2x60Hz = 120Hz. In case a frequency converter is applied its frequency can be monitored on the device and is a fixed value.

For the amplitude, however, it is a different issue. It depends on many other influencing factors, such as weight of mixing device, fluid density and viscosity or size and shape of mixing plate. This leaves no other option but measure the actual physical displacement of the plate.

Visual measurement 

Traditionally, amplitude is visually measured with the help of a self-adhesive strip placed on the shaft of the mixer which oscillates along with the mixing plate. On the strip there are two lines forming an arrow. When the device oscillates the arrow appears as two arrows forming an intersection point at which the actual amplitude can be gauged. Although it is a quick and dirty means to measure amplitude it is not easy to get the reading right, as it leaves room for interpretation with each person seeing something else.

Electronic measurement (VM-021)

Later an electronic instrument was developed which consists of a piezo sensor fixed on the shaft of the mixer. The acceleration measured by the piezo is a linear function with respect to amplitude and with some conversion it gives an analog signal which can be used to monitor amplitude and control the drive unit. As the instrument interprets the amplitude based on acceleration data it needs to be calibrated for each FUNDAMIX® separately. Additionally, the sensor is mounted on the shaft and it cannot be easily transferred from one unit to the other. It is usually applied as a fixed installation.

Hand-held laser measurement

As an alternative to the above instruments we have developed an optical laser sensor. It measures the distance to an oscillating plate fixed on the shaft of the mixer every 1.5 ms. These values are algorithmically converted into an analog reading shown on an integrated display. As we are measuring an absolute distance there is no requirement for additional calibration. This allows the instrument to be applied to all FUNDAMIX® agitators equally, irrespective to other influencing factors such as frequency. As the sensor is not fixed to the vibratory part of the equipment it can be applied as a hand-held battery-operated device to be easily carried around. This marks a new generation of amplitude monitoring instruments and we are proud to offer this to our clients.