Centrifuge · Calibration procedure
Speed verification
Measures the actual rotor speed with a calibrated optical tachometer and compares it with the set speed.
PURPOSE
Why this is checked
Separation depends on RCF, which rises with the square of the speed. A centrifuge that runs slow may leave sample extracts cloudy; one that runs fast can exceed tube or rotor ratings.
Frequency
Typically every 6 or 12 months and after motor or controller repair, as defined in your calibration SOP.
Learn how the Centrifuge worksYOU WILL NEED
Standards & tools
- Calibrated non-contact (optical) tachometer with reflective tape, traceable to national standards
BEFORE YOU START
Prerequisites
- Reflective tape fixed to the rotor or hub
- Rotor balanced (empty or with balanced tubes)
- Access port or transparent lid window available; never bypass the lid interlock
PROCEDURE
Step by step
- 1Select speeds across the working range, e.g. 1000, 2000 and 4000 rpm.
- 2Run at the first speed and wait until it is stable.
- 3Aim the tachometer through the viewing port at the reflective tape and take three readings.
- 4Repeat for each speed and calculate the mean and % error.
- 5Optionally convert the measured speed to RCF for the rotor radius used in methods.
RECORD
Example observation table
| Set speed (rpm) | Reading 1 | Reading 2 | Reading 3 | Mean (rpm) | % error |
|---|---|---|---|---|---|
| 1000 | 998 | 1003 | 1001 | 1000.7 | +0.07 |
| 2000 | 1994 | 2004 | 1998 | 1998.7 | −0.07 |
| 4000 | 3992 | 4006 | 3998 | 3998.7 | −0.03 |
CALCULATION
How to calculate the result
% error = (Mean measured rpm − Set rpm) ÷ Set rpm × 100; RCF = 1.118 × 10⁻⁵ × r (cm) × rpm²
- At 4000 rpm: mean = (3992 + 4006 + 3998) ÷ 3 = 3998.7 rpm
- % error = (3998.7 − 4000) ÷ 4000 × 100 = −0.03%
- RCF for a 10 cm radius at 4000 rpm = 1.118 × 10⁻⁵ × 10 × 4000² = 1788.8 × g (about 1789 × g)
- Reverse use: for 3000 × g at r = 15 cm, rpm = √(3000 ÷ (1.118 × 10⁻⁵ × 15)) ≈ 4230 rpm
ACCEPTANCE CRITERIA
Pass if
- Measured speed typically within ±2% of the set speed (or ±50 rpm, whichever your SOP specifies).
IF IT FAILS
What to do
- Label the centrifuge 'Out of calibration' and stop using it.
- Arrange service of the motor or speed controller.
- Assess methods that depend on a minimum RCF for impact since the last passing check.
MORE
Other Centrifuge calibrations
In LimsPulse · Calibration Management
LimsPulse schedules this calibration, records the result against limits, and blocks the instrument everywhere if it fails or goes overdue.