By the end of this chapter, you will be able to:
Mastering these skills ensures you keep centrifuge equipment safe, reliable, and ready to support important laboratory work every day.
Centrifuges are fundamental diagnostic and laboratory equipment widely used in Kenyan biomedical engineering settings, including hospitals, research institutions, and clinics. Understanding the principles and functions of centrifuges is critical for biomedical engineers tasked with equipment maintenance and troubleshooting, ensuring accurate test results and patient safety. This chapter explores the scientific basis of centrifuge operation and its practical roles in laboratory diagnostics, guiding professionals in effective maintenance practices.
The operation of a centrifuge relies on fundamental physical principles that separate components of a mixture based on density differences using centrifugal force. Biomedical engineers working in hospital laboratories like Kenyatta National Hospital must grasp these principles to optimize centrifuge performance and prevent mechanical failures. This section dissects the core scientific concepts underpinning centrifuge function.
Centrifugal force is the apparent force exerted outward on a body moving around a center, arising from inertia. In a centrifuge, this force is generated by rapidly rotating the rotor holding sample tubes. The faster the rotation, the greater the centrifugal force, enabling the separation of substances based on density. For example, in a blood sample, denser components such as red blood cells move outward, while plasma remains closer to the center.
Sedimentation is the process by which particles settle out of a fluid under the influence of gravity or centrifugal force. A centrifuge accelerates sedimentation by applying a force many times stronger than gravity, causing components with different densities to separate into distinct layers. In diagnostic laboratories, this allows separation of blood components for tests like hematocrit or serum analysis.
The magnitude of centrifugal force depends on rotor speed (angular velocity) and the radius of rotation. The force increases with the square of the speed and linearly with radius, making both parameters critical for effective separation. Biomedical engineers must ensure the rotor speed matches the equipment specifications and that the radius is appropriate for the sample tubes used to avoid sample damage or equipment strain.
Relative Centrifugal Force (RCF) quantifies the force applied to samples relative to Earth's gravity and is a key parameter in centrifuge operation. RCF is calculated using the formula:
RCF = 1.118 × 10^-5 × r × (RPM)^2
Where:
r = radius in centimeters
RPM = revolutions per minute
This formula enables technicians to calibrate centrifuge settings accurately for specific laboratory protocols, ensuring consistent and reliable separation outcomes.
Explain how centrifugal force is generated in a centrifuge and its role in sample separation. (6 marks)
Calculate the RCF for a centrifuge rotor with a radius of 15 cm operating at 3000 RPM. Show all steps. (8 marks)
Create a free account to open more of this chapter.
Free: practical guides, quick cards, workplace scenarios and more.
Create a free accountThis chapter explored the principles underlying the operation of a centrifuge, explaining how centrifugal force separates substances based on density. The function of a centrifuge was described as a critical process in diagnostic and laboratory settings for separating components such as blood cells and plasma. The main parts of a centrifuge, including the rotor, motor, and control panel, were outlined to provide a clear understanding of its construction. Various types of centrifuges were examined, ranging from manual and electrical models to specialized versions like tabletop, haematocrit, ultracentrifuge, and refrigerated centrifuges, each designed for specific laboratory needs. The operational principles focused on balancing speed, time, and sample volume to achieve effective separation. Control devices such as timers, speed regulators, and safety locks were detailed to highlight their role in precise and safe usage. Maintenance procedures emphasized regular cleaning, inspection, and lubrication to ensure optimal performance and longevity. Finally, safety procedures were underscored to prevent accidents and protect both the operator and the equipment during centrifuge operation.
Type: Individual
| Tools & Equipment | Materials |
|---|---|
| Laboratory centrifuge model Hettich EBA 20 | PPE: Lab coat, gloves, safety boots |
| Marker pen | |
| Sticky notes | |
| Instruction manual for Hettich EBA 20 centrifuge |
| S/N | Item | Quantity |
|---|---|---|
| 1 | Laboratory centrifuge model Hettich EBA 20 | 1 Pc per Candidate |
| 2 | Sticky notes | 10 Pcs per Candidate |
| 3 | Marker pen | 1 Pc per Candidate |
| 4 | Instruction manual for Hettich EBA 20 centrifuge | 1 Pc per Candidate |
| 5 | Power supply (220V) | 1 Pc per Candidate |
| 6 | PPE: Lab coat, gloves, safety boots | 1 set per Candidate |
| Items to be Evaluated | Marks Available | Marks Obtained | Comments |
|---|---|---|---|
| TASK 1: Demonstrate knowledge of centrifuge principles | |||
| Wore the required PPE: lab coat, gloves, safety boots (Award 1 mark for each PPE worn = 3 marks) | 3 | ||
| Identified and labeled the major parts of the centrifuge using sticky notes: chamber, rotor, lid, latch, controls, tube holder (Award 1 mark for each correctly identified part = 4 marks) | 4 | ||
| Explained the principle of centrifugation: separation by density using centrifugal force (Award 3 marks for a clear and accurate explanation) | 3 | ||
| Described the operation steps: placing tubes in rotor, balancing, closing lid, setting speed/time, starting the machine (Award 3 marks for correct sequence and explanation) | 3 | ||
| Discussed safety precautions during operation (Award 2 marks for mentioning at least two safety measures) | 2 | ||
| Answered questions on how centrifuge separates substances based on density and sedimentation (Award 3 marks for clear and accurate answers) | 3 | ||
| Sub-Total | 18 | ||
| PRODUCT CHECKLIST | |||
| Clear and accurate labeling of centrifuge parts with sticky notes (Award 5 marks for all parts correctly labeled and positioned) | 5 | ||
| Comprehensive explanation covering principles, operation steps, and safety (Award 7 marks for completeness and clarity of explanation) | 7 | ||
| Sub-Total | 12 | ||
| GRAND TOTAL | 30 | ||
Type: Individual
| Tools & Equipment | Materials |
|---|---|
| Centrifuge machine | Distilled water |
| Microcentrifuge tubes | Lens cleaning solution |
| Set of screwdrivers | Clean microfiber cloth |
| Marker pen | 70% isopropyl alcohol |
| Medical lint-free wipes | |
| Sticky notes | |
| PPE (Lab coat, gloves, safety boots, surgical mask, surgical cap) |
| S/N | Item | Quantity |
|---|---|---|
| 1 | Centrifuge machine | 1 Pc per Candidate |
| 2 | Microcentrifuge tubes | 10 Pcs per Candidate |
| 3 | Distilled water | 50 ml per Candidate |
| 4 | Lens cleaning solution | 10 ml per Candidate |
| 5 | Clean microfiber cloth | 1 Cloth per Candidate |
| 6 | 70% isopropyl alcohol | 50 ml per Candidate |
| 7 | Medical lint-free wipes | 10 Pcs per Candidate |
| 8 | Sticky notes | 10 Pcs per Candidate |
| 9 | Marker pen | 1 Pc per Candidate |
| 10 | Set of screwdrivers | 1 Set per 3 Candidates |
| 11 | PPE (Lab coat, gloves, safety boots, surgical mask, surgical cap) | 1 Set per Candidate |
| 12 | Electric power supply | 1 Pc per Candidate |
| Items to be Evaluated | Marks Available | Marks Obtained | Comments |
|---|---|---|---|
| TASK 1: PPE and Preparation | |||
| Wore all required PPE: Lab coat, gloves, safety boots, surgical mask, surgical cap (Award 1 mark for each PPE worn = 5 marks) | 5 | ||
| Maintained a clean and organized working area (Award 1 mark for a clear working area) | 1 | ||
| Sub-Total | 6 | ||
| TASK 2: Identification and Cleaning | |||
| Identified centrifuge parts: Chamber, Lid, Latch, Controls, Rotor, Tube holders (Award 1 mark for each correctly identified part = 5 marks) | 5 | ||
| Cleaned centrifuge surfaces using lens cleaning solution and lint-free wipes (Award 1 mark for correct cleaning procedure) | 1 | ||
| Disinfected the rotor and tube holders using 70% isopropyl alcohol (Award 1 mark for proper disinfection) | 1 | ||
| Covered open ports before cleaning (Award 1 mark for covering open ports) | 1 | ||
| Sub-Total | 8 | ||
| TASK 3: Functionality Test and Fault Diagnosis | |||
| Connected the centrifuge to power supply and switched on the mains (Award 1 mark for correct connection and power on) | 1 | ||
| Loaded balanced tubes with distilled water into rotor correctly (Award 1 mark for proper tube loading and balancing) | 1 | ||
| Started centrifuge and observed rotor rotation (Award 1 mark for starting centrifuge properly) | 1 | ||
| Diagnosed fault by disconnecting power and checking fuse integrity when centrifuge failed to start (Award 2 marks for correct fault diagnosis procedure) | 2 | ||
| Replaced faulty fuse using appropriate tools (Award 1 mark for correct fault repair) | 1 | ||
| Reconnected power and retested centrifuge functionality with successful rotation (Award 5 marks if centrifuge rotates successfully after repair, else zero) | 5 | ||
| Sub-Total | 11 | ||
| TASK 4: Documentation | |||
| Prepared a service report including date, machine name, observations before and after troubleshooting, and maintenance actions (Award 1 mark for complete and accurate service report) | 1 | ||
| Correctly filled a preventive maintenance sticker and affixed it on the centrifuge (Award 1 mark for proper PPM sticker completion) | 1 | ||
| Sub-Total | 2 | ||
| PRODUCT CHECKLIST | |||
| Centrifuge operates smoothly with balanced load and no unusual noise or vibration (Award 5 marks for proper machine operation) | 5 | ||
| Sub-Total | 5 | ||
| GRAND TOTAL | 32 | ||
At the start of this chapter we promised you would be able to:
Tick each one you can genuinely do.
So, are you there yet?
You're competent when you can confidently do 50% or more of what this chapter promised.
Sign in to record how you're doing.