Weighting a Vaccine
- Thorsten A. Kern
You are requested to design a load-cell to automize the process of dosing vaccine into containers. The nominal/target weight of one dose is 5 gram and has a volume of 4.0 ml. The weight of the container is 10 gram +/- 1 gram. The fixture to hold the container while dosing has a weight of 120 gram with an uncertainty due to the automation process (cables dangling, pipes) of +/- 5 gram. The dosing-system is controlled by your sensor and induces by switching delays an error of +/- 0.1 %. You can dose any volume. The container is designed to carry a maximum safe volume of 20 ml.
Your design-target of the measurement is to ensure enough vaccine for five doses to be in the container. Overdosing (more vaccine) is acceptable. Too little dosing (less vaccine than required for five doses) is unacceptable.
a) You have three force-sensors to choose form as a load-cell. Which force-sensor do you choose if you want to achieve the lowest absolute dosing error? Explain your choice!
| Sensor 1 | Sensor 2 | Sensor 3 | |
|---|---|---|---|
| Force Nominal Value [N] | 1 | 3 | 5 |
| Force max specified value [N] | 5 | 5 | 5 |
| Measurement-Uncertainty in nominal range [% from nominal value] | 2% | 1% | 1% |
| Measurement Uncertainty above nominal range [% from max-value] | 50% | 10% | 5% |
b) Do an error-calculation considering all parameters of the setup and your choosen force-sensor. What is the maximum relative error your system has for five doses? Explain your calculation!
c) How much vaccine in milliliter do you need to dose to ensure considering all errors that at least five doses are available in the container? Explain your consideration!
d) An obvious improvement is a step of "tara"/ to calibrate the weight after the container is placed on the fixture. If you consider that a one-time tara happens before the dosing begins with just the vaccine on the fixture in a still position, how much vaccine do you need to dose then to ensure considering all errors that at least five doses are available in the container? Explain your consideration!
e) Become creative: What other type of measurement would you choose (maximum of two examples) to control the dosing process beside weighting/force-measurement. Make sketches of how such a setup could look like. Discuss Advantages and Disadvantages you can think of.
Point-Distribution:
- In an exam, 70% of the points would be on a) to d) and 30% of the points would be on e)
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