Gas detectors help with drug tablet coating thickness

Sensitive detectors, from Minneapolis-based Sensor Electronics, monitor ethanol gas concentrations in the exhaust streaming from the coating machine.


Gas detector (white) looks for leaks inside the cabinet holding the mechanical system operating the sprayer and tumbler. Besides showing actual ethanol levels in LEL percentage, the detector has LEDs that glow green/amber/red, reflecting any increase in ethanol intensity. Courtesy: Sensor ElectronicsSophisticated gas detectors help a pharmaceutical manufacturer, Paddock Laboratories, measure coating thicknesses on drug tablets. The sensitive detectors, from Minneapolis-based Sensor Electronics, monitor ethanol gas concentrations in the exhaust streaming from the coating machine.

While the detectors protect plant personnel, said John Levasseaur, production engineer, Paddock Laboratories, using them to monitor coating thickness is especially intriguing.

Technical engineer John Levasseur inspects mounting for spray head feeding ethanol-based tablet coatings. Duct opening (lower left) carries exhaust gases. Courtesy: Sensor ElectronicsTablet bases are fed into a twirling tumbler where a small-bore feeder sprays a bonding mist of the ethanol carrier, plus a color tint, a lubricant (for easier swallowing), or the drug itself. Depending on the coating, the tablets are tumbled from 30 minutes up to 4 hours, with close monitoring of the ethanol feed, temperature, and humidity.

The ethanol concentration in the exhaust is directly proportional to the coating thickness on the tablets. A too-high ethanol level means a too-thick coating, so the spray mist ratio is decreased. The ethanol proportion in the exhaust then verifies the feeder setting.

Tablet-filled basket tumbles inside stainless-steel housing; ethanol gas carries tin/lubricant/drug coating feeding through arm extending into basket. Depending on coating, tumbling times range from 30 minutes to 4 hours. Courtesy: Sensor ElectronicsThe gas detectors do double duty. Ethanol is explosive, so if ethanol levels in the exhaust duct reach a preset LEL (lower explosion limit), then the detector triggers alarms to warn workers. If the ethanol concentration continues to rise, the gas detection system turns on fans to flood the area with outside air.

Paddock Laboratories concentrates on niche markets for generic drugs. “But with any generic drug—or any drug, for that matter—reliability is the key. Closely monitoring ethanol levels in our coating process helps us maintain that reliability,” Levasseaur said.

- Tom Probst, corporate communications, Sensor Electronics Corp.

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