Development of a capacitance sensing system for monitoring moisture content of spray dried gelatin powders

• A capacitive sensor was built to measure moisture content (MC) of spray dried gelatin powders.
• A mass-based off-line mode was built to validate the capability of the sensor.
• An on-line non-contact mode was built to measure MC of dynamic samples.
• The capacitive sensor also showed the capability to reflect spatial distribution of deposition during spray drying.

For on-line, non-contact measurement of moisture content (MC) of spray dried products, a capacitance sensing system was developed using pairs of copper plates attached to the perimeter of the spray dryer measuring cylinder. The plates formed capacitors which were sensitive to changes in dielectric properties, which in turn were related to MC. The self-built system was tested on spray dried gelatin powders in three modes: a) an off-line mode to test the capabilities of the sensor at different MC levels (4%–44% (d.b.)); and b) an on-line mode to measure MC of samples passing through the sensor enclosure. Results indicated this system was feasible to measure MC both statically and dynamically, but it had better performance for off-line samples (R2 = 0.98, RMSE = 1.9%); c) this system was also used in an ECT mode and showed the capability to reflect spatial distribution of deposition during spray drying.