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Technical Note

High Precision Mass Inspection with Accuracy of ±0.5 mg* Achieved

Anritsu's capsule checkweighers have achieved the industry's highest weighing precision* of ±0.5 mg. Here, we will describe the background as to why there is a demand for high precision mass inspections and also provide an explanation of the newly developed balance used in our capsule checkweigher.

* The highest weighing precision of ±0.5 mg is based on our survey results.

Capsule Checkweigher

Background showing the need for high precision mass inspections

●Appearance of next generation capsules

The most widely used general purpose capsules are currently "animal-derived capsules" that use gelatin as their raw material. However, for health and religious reasons, "plant-derived capsules" have come into use.

Appearance of next generation capsules

There are likely to be variations in the mass of plant-derived capsules during production; therefore, highly precise mass control is required.

●Increase in highly active pharmaceutical preparations (such as anticancer drugs and immunosuppressants)

The number of highly active pharmaceutical preparations is increasing. Even a slight variance in the fill content can change their efficacy, and variability in the mass of the capsules themselves cannot be ignored.

Increase in highly active pharmaceutical preparations (such as anticancer drugs and immunosuppressants)

Because variability in the pre-filled (prelock) capsules results in variability in the elution time and amount of active ingredient, in addition to mass control of filled capsules, the mass of capsules prior to filling needs to be strictly controlled for highly active pharmaceutical preparations.

Anritsu's balance has achieved the industry's highest weighing precision

●From the differential transformer method to the force balance method

Our proprietary balance that employs the differential transformer method was used in conventional devices utilizing silicone oil as a damper and the displacement in the structural body using a spring is converted into an electric signal by the differential transformer to obtain the mass. Although it was highly precise (±2 mg) in 1997, due to degradation of oil and distortion of the balance (the mechanism) from prolonged use, regular maintenance was required.

●Principle of the force balance method that enabled high precision of ±0.5 mg to be achieved

In the force balance method, the load is balanced with a mechanical balance mechanism using a positioning sensor and an electromagnetic force. The mass is obtained from the size of the force coil current required for balancing. This enabled high precision of ±0.5 mg to be achieved, and because the mechanism does not require oil or use of a spring, this means negligible deterioration of mechanical parts, and no need for maintenance.

the force balance method
Principle of the force balance method that enabled high precision of ±0.5 mg to be achieved

●Resistant to extraneous vibration, provides consistent high precision

This method is more responsive than the differential transformer method, enabling highly precise mass measurements. Additionally, with a mechanism that makes fine adjustments to the balance state under a no-load condition, the impact of extraneous vibration was able to be reduced successfully.

Resistant to extraneous vibration, provides consistent high precision

●Summary

Industry's highest weighing precision of ±0.5 mg enhances both the production and mass check of pharmaceutical products.
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