1. Necessity of Detection: The Key to Ensuring Accurate Experimental Results

Laboratory centrifuges are widely used in laboratories of hospitals, scientific research institutions, food and drug inspection institutions, etc., with a maximum rotational speed usually not exceeding 30000 r/min. As a core technical parameter of centrifuges, rotational speed directly determines the magnitude of centrifugal force. If the rotational speed fails to meet the standard, suspensions or emulsions cannot be completely separated, which may lead to inconsistent experimental conclusions for the same substance separated by different centrifuges—seriously affecting the accuracy of tests. At present, due to the lack of dedicated verification procedures and calibration specifications, the verification/calibration of centrifuges is difficult to carry out. Therefore, it is highly necessary to explore their metrological detection methods.

In terms of function, centrifuges can achieve solid-liquid and liquid-liquid separation, remove liquid from wet solids, and special types can even separate gas mixtures or classify solid particles. They are core equipment for sample pretreatment in fields such as biology, clinical medicine, and laboratory medicine. Regular metrological detection is an important prerequisite for ensuring their centrifugal accuracy.

2. Basic Detection Methods: Specifications for Rotational Speed and Temperature Measurement

2.1 Basic Operation for Rotational Speed Measurement

When using a fixed frequency meter to measure rotational speed, it must be firmly fixed on the metal shell of the centrifuge or a tripod to ensure measurement safety. After the centrifuge operates stably at the calibration point, measure the rotational speed 10 consecutive times to calculate the average value and indication error. At the same time, use a stopwatch to measure the actual operation time; if a mechanical timer is used, its accuracy must be verified to meet the requirements.

2.2 Temperature Calibration for Low-Temperature Refrigerated Centrifuges

Low-temperature refrigerated centrifuges require additional temperature calibration: after turning on the machine for pre-cooling, use deionized water to simulate samples, operate according to the set centrifugation conditions, and immediately measure the temperature of deionized water with an electronic thermometer after centrifugation. The measurement can be repeated several times or conducted under different centrifugation conditions, and temperature calibration is completed by calculating the average value and error.

3. Targeted Rotational Speed Measurement: Operation by Centrifuge Type

3.1 Open-Top and Covered Types with Acrylic Observation Windows

Before measuring these types of centrifuges, attach reflective paper to an appropriate position on the rotating arm or shaft, and align the photoelectric sensor with the reflective mark—either directly or through the acrylic observation window. Set the rotational speed as required, start the centrifuge, and after it operates stably, the value displayed on the tachometer is the actual rotational speed.

3.2 Covered Types Without Observation Windows

For measurement, a dedicated speed sensor with strong magnets and a flexible spiral support rod is required. Relying on the magnetic attraction of the magnets to the centrifuge cover and cabinet, fix the sensor on the inner side of the upper cover, aligning it with the reflective mark on the rotating arm or shaft. Use the flexible spiral support rod to lead out signals from the light source, photoelectric receiving, and conversion devices. After connecting to the speed measurement device, complete the measurement following the same startup and reading procedures.

4. Rotational Speed Correction and Calibration: Improving Equipment Operation Accuracy

For rotational speed correction, a correction factor should be introduced based on the indication error to adjust the centrifuge’s set value. If the corrected rotational speed or temperature still fails to meet the standard, repeated correction and measurement are required until the error meets the requirements. Data shows that after correction, the rotational speed error of most centrifuges can be controlled within ±25 r/min (accounting for 90%) or even ±15 r/min (accounting for 70%), the maximum relative error is reduced from 16.435% to 0.761%, and the temperature error is reduced from -3.33°C to -0.43°C.

There are two ways to select calibration points:

Linear selection starting from the maximum rotational speed, covering common rotational speeds and selecting as many points as possible—suitable for newly installed equipment or comprehensive detection;

Setting calibration points based on the actual common rotational speeds of the centrifuge to ensure accurate operation of the equipment under daily used rotational speed conditions.

5. Positioning Test Technology: Accurately Obtaining Key Parameters

Positioning tests utilize the characteristic of capacitive micrometers that output a fixed voltage when over-range. A positioning test area is designed on the precision centrifuge. When the test area reaches or leaves the capacitive micrometer, the instrument enters the saturation zone and outputs a full-range fixed voltage. By using software to identify the effective test data between the two full-range voltage segments, the original measurement value of the dynamic pitch misalignment angle can be obtained. This technology can effectively separate test signals, has high measurement accuracy, and is feasible for practical application.

In the context where relevant national verification procedures and calibration specifications have not yet been issued, the above detection methods can provide effective support for centrifuge acceptance testing and daily metrology, ensuring the accuracy and reliability of experimental test results.