Study on the measuring device of medical centrifuges

This paper designs a measuring and detecting device for medical centrifuges. The device integrates the measurement of rotational speed, temperature, and time. The photoelectric tachometer was transformed into a laser speed detection module to adapt to the rotational speed measurement of the closed centrifuge and a wireless temperature detection module could be inserted into the slot of the centrifuge tube to measure the temperature of the tube position when the centrifuge rotates at a high speed. This method achieved reliable and accurate measurement of the speed, temperature, and time of various centrifuges with low costs.


Introduction
Medical centrifuges are commonly used in medical laboratories or biochemical experiments.Medical centrifuges use rapid rotation to rapidly precipitate suspended particles in mixtures to separate various substances and components with different values of specific gravity.To separate samples, it is necessary to maintain the corresponding centrifugal rotational speed and set the centrifugation time when the medical centrifuge is used for the pre-treatment of a medical laboratory or a biochemical experiment.To prevent some of the high-temperature resistant substances from deteriorating due to friction heat, temperature control may also be used.Therefore, the accuracy of rotational speed, temperature, and time directly affects the centrifugal effect and thus test results.It is very important to conduct quantitative detection and control the accuracy of these three parameters for medical centrifuges.
At present, there are a variety of measurement methods for the rotational speed of medical centrifuges, mainly including photoelectric, magnetoelectric, and vibrating types.In Zhao et al.'s work [1] , a photoelectric tachometer was proposed to measure the speed of medical centrifuges.A reflection mark is pasted on any rotating arm of the centrifuge and the photoelectric tachometer is used to measure the observation hole of the centrifuge.This method is accurate and reliable, and the detecting equipment has multiple models and low costs, but it is only applicable to centrifuges with observation holes.More than 30% of medical centrifuges without observation holes are closed in the market, so rotational speed measurement cannot be done by this method.An electromagnetic sensor is used to measure the rotational speed of the medical centrifuge at Hunan University.In this method, a magnet is attached to the inner wall of the medical centrifuge, and a Hall sensor is placed in the test tube of the rotating shaft of the medical centrifuge.The Hall sensor is used to detect the number and time of pulses, and the rotational speed of the medical centrifuge is calculated [2] .This method can be used to measure medical centrifuges with or without observation holes, but the installation is difficult, and because of the shielding effect of the metal rotor, the anti-interference ability and the accuracy of speed measurement are poor.Li et al. [3] from Shenyang University of Technology proposed a principle of vibration measurement.A vibration sensor is fixed on the outer shell of a medical centrifuge to measure rotational speed.It can effectively measure both types of medical centrifuges (with and without observation holes).However, this method has high equipment costs and low economic efficiency Moreover, it requires unbalanced objects placed in the medical centrifuge to achieve vibration, and the rotor of the medical centrifuge can be easily damaged by a slightly improper operation.
At present, the commonly used method for temperature measurement of medical centrifuges is to place the wired temperature sensor into the centrifuge chamber for measurement [4] .In order to avoid touching the temperature sensor during the high-speed rotation of the centrifuge, this method is generally used when the equipment is in a static state.However, in a non-centrifugal state, there is no internal airflow, and the temperature distribution is extremely uneven.In addition, the rotor of the centrifuge generates heat due to friction during rotation, so the actual temperatures in a static state and a centrifugal state differ enormously.In addition, the method for temperature measurement is to firmly paste the temperature sensor on the inside of the cavity wall of the medical centrifuge, so that the temperature is measured after the rotor of the medical centrifuge rotates.However, because the refrigeration system of the medical centrifuge is generally used for cavity wall refrigeration, the temperature of the inner wall of the medical centrifuge is significantly lower than that of the tube, and the measured temperature is not accurate [5] .

Overall scheme design of medical centrifuge measuring device
In order to solve the difficulties and problems in the measurement and detection of centrifuges, this paper designs a measuring and detecting device for medical centrifuges.The device integrates the measurement of rotational speed, temperature, and time.The photoelectric tachometer was transformed into a laser speed detection module to adapt to the rotational speed measurement of the closed centrifuge and a wireless temperature detection module could be inserted into the slot of the centrifuge tube to measure the temperature of the tube position when the centrifuge rotates at a high speed.This method achieved reliable and accurate measurement of the speed, temperature, and time of various centrifuges with low costs.
This detecting device mainly includes a main control unit, a laser speed detection module, a wireless temperature detection module, etc., as shown in Figure 1.In addition, the temperature acquisition unit is equipped with a weight unit (Number 6), which is consistent with the wireless temperature collector to ensure smooth rotation of the medical centrifuge.The main control unit (Number 3) is also connected to a clock module to display and calculate centrifuge running time; the collected speed, temperature, and time values are all displayed on the display screen simultaneously through the main control unit.

Design of rotational speed measurement module
This rotational speed measurement module uses infrared laser feedback technology, as shown in Figures 1 and 2. Number 22 represents the laser transmitting and receiving unit, which is connected to the main control unit (Number 3) through an optical fiber.Number 21 represents the reflection unit, which is pasted and fixed on the rotating platform of the medical centrifuge rotor.Number 22 emits infrared light, and with every turn of the rotor, the reflection unit (Number 21) reflects an infrared light signal to Number 22.The reflected light is transmitted back to the main control unit (Number 3) through the optical fiber, and the main control unit (Number 3) calculates the speed of the medical centrifuge by calculating the frequency of the reflected light.Every time a laser signal is received, the rotating platform inside the medical centrifuge rotates for one round.

Design of temperature measurement module
As shown in Figures 1 and 2, the wireless temperature collector (Number 1) is inserted into the centrifuge tube slot of a medical centrifuge to measure the temperature in the centrifuge tube slot.The collector, which is shaped like a centrifuge tube, contains a high-precision temperature sensor, a battery, a signal transmitter, and a flexible circuit board.All the above components are integrated into a small unit with a diameter of 22 mm.In order to avoid the Doppler effect of signals and ensure the stable and continuous transmission of temperature signals during rapid rotation, this module adopts wireless transmission to output temperature data, and the wireless receiving unit (Number 5) is fixed on the internal top cover of the medical centrifuge, transmitting the data it obtains to the main control unit (Number 3) through the signal line and then displaying the temperature data in real time through the display screen.
Because the items placed in the rotor of the medical centrifuge need to be balanced, we designed a counterweight unit (Number 6).Its weight is equivalent to that of the wireless temperature detection unit (Number 1) and its centrifuge tube corresponds to the centrifuge tube slot of the wireless temperature detection unit (Number 1) during use to ensure balanced and stable high-speed rotation of the medical centrifuge rotor.

Design of the main control unit
The main control unit is the overall control platform and data summary platform of the whole medical centrifuge measuring and detecting device, and its structure is shown in Figure 3.
The outer shell of the main control unit is arranged with a display screen, operation keys, and a USB Type-C interface.The microprocessor is located in the shell, and the built-in clock module is used to display and calculate the running time of the centrifuge.The microprocessor is connected to the display screen, operation keys, wireless receiving module, laser sensor, and the outer end of the transmitting fiber and receiving fiber connection.The power module is powered by lithium batteries and charged through a Type-C interface.

Test and analysis of the device
4.1 Scheme of device test [7[8][9] In order to verify the measurement accuracy of the device, the device, the photoelectric tachometer, and the vibrating type measuring instrument for centrifuge rotational speed was used to measure the rotational speed of the same centrifuge (with the same rotor installed) (for the convenience of comparison, a medical centrifuge with observation holes was selected for measurement); the device and the wired temperature inspecting instrument were used to measure the temperature of the same centrifuge (a low-temperature centrifuge was selected).Timing measurements were performed on the same centrifuge using this device and a stopwatch, respectively.
1) The device was used for the quantitative detection of medical centrifuges [10][11] .
The medical centrifuge was placed on a stable horizontal table, the wireless temperature recording module and its counterweight were placed symmetrically in the rotor of the centrifuge, and a test tube filled with water was placed in one of the other free positions to load the medical centrifuge to a full load.
The centrifuge top cover was opened, and the reflection unit was pasted on the rotating platform of the rotor of the medical centrifuge.The laser transmitting and receiving module of the device was pasted and fixed on the bottom of the medical centrifuge top cover.After the top cover of the medical centrifuge was closed, the transmitting optical fiber, the receiving optical fiber, and the wire of the wireless receiving unit were extended through the opening gap of the medical centrifuge, and then connected to the main control unit.
Then the pre-cooling of the medical centrifuge started, and the temperature measurement value of the medical centrifuge in a static state was read on the device after the set temperature was reached.
After that, the medical centrifuge started to cool and rotate, and the set temperature and speed were reached.After the medical centrifuge reached stability, the measurement values of rotational speed, temperature, and timer time of the medical centrifuge were read on the display screen of the device.
2) The rotational speed was measured by the photoelectric tachometer and vibration speed measuring instrument.
The top cover of the medical centrifuge was opened, and then the tube was installed, fill with water, and placed in the tube position.After that, the medical centrifuge was loaded to a full load, the reflective strip was attached on the rotating platform of the rotor to the position of the observation hole, and the vibration probe of the vibration meter was stuck on the outer wall of the medical centrifuge side.After the top cover of the medical centrifuge was closed and the centrifuge was started to reach the set rotational speed, the rotational speed of the medical centrifuge was measured by pointing the observation hole with the photoelectric tachometer, and the value of the measured rotational speed was read at the terminal of the vibrating type speed measuring instrument.
3) The temperature was measured with a wired temperature inspecting instrument.The temperature probes 1 and 2 of the wired temperature inspecting instrument were inserted through the bottom of the medical centrifuge and pasted on the inner and middle inner walls of the bottom of the medical centrifuge, respectively.Probe 3 was inserted through the gap of the upper cover and placed in the placement position of the centrifuge test tube.Then the power supply of the centrifuge was turned on, the temperature was set, and the centrifuge was pre-cooled.After the temperature of the medical centrifuge reached stability, the temperature measurement values of Probes 1, 2, and 3 were read.Then Probe 3 was removed, the centrifuge rotor was started to reach the set speed and stabilized, and the temperature measurement values of Probes 1 and 2 were read [6] .
4) The timer time was measured with a stopwatch.The centrifuge timer time was set, and the stopwatch measurement was started when the speed reached the set value.

Results of device test
According to the test method, the speed, temperature, and time of H2050R, LC-LX-H185C, Microfuge 20, Legend Micro 17, and TGL16M were measured (the five devices numbered 1, 2, 3, 4, and 5 respectively).To cover the measurement range of the five types of equipment, three measurement points-1000 r/min, 5000 r/min, and 15000 r/min-were selected for speed, 5℃ for temperature, and 5 min for time.The data obtained are as follows.

Statistical analysis
By comparing with other methods of centrifuge measurement, we obtained the following results from a statistical analysis: 1) From the Figure 4-6, we can see that the results of the rotational speed measurement experiment for this device, photoelectric tachometer, and rotational speed measuring instrument are basically the same, which proves that the rotational speed measurement of this device is accurate and reliable.
2) From the Figure 7, we can see the result of temperature measurement.In this experiment, when the medical centrifuge was not rotating, the temperature at the test tube position was also measured.The temperatures measured by this device are consistent with those measured by the wired temperature inspecting instrument, which proves that the temperature measurement of this device is accurate and reliable.The wired temperature inspecting instrument detected different temperatures at the bottom, side wall, and tube position of the centrifuge, and the device detected different temperatures when the centrifuge rotor was rotating and not rotating, which proves the necessity of the design and use of the device.Because the use of a low-temperature centrifuge is to ensure that the temperature of the material to be centrifuged is within the control range, it is more practical to measure the temperature of the tube position during the rotation of the rotor when testing the medical centrifuge.
3) From the Figure 8, we can see that in the time measurement experiment, the time measured by the device and the stopwatch are basically the same, which proves that the time measurement of the device is accurate and reliable.This device can automatically measure time and speed synchronously, which is more convenient for practical use.

Conclusion
This paper takes the measurement and detection of medical centrifuges as the research object.Starting from the detection requirements of medical centrifuges, this paper uses a laser reflection tachometer, a wireless temperature sensor, a timing counter, and other common, low-cost equipment to achieve accurate measurement of rotational speed, low-temperature centrifuge temperature and centrifugation time for medical centrifuges.Moreover, the proposed device has good portability, practicability, and operability with low costs and high safety standards.

Figure 1 .
Figure 1.Three-dimensional diagram of the detecting device for a medical centrifuge.In the three-dimensional diagram of the detecting device, Part 1 is the host screen; Part 2 is the photoelectric circuit and photovoltaic system; Part 3 is the temperature signal reception system; Part 4 is the battery; Part 5 is the optical fiber; Part 6 is the main control unit, containing Parts 2-4; Part 7 is the laser speed measurement module; Part 8 is the wireless temperature detection module, whose probe is small and can be put in the test tube.

Figure 2 .
Figure 2. Graphical representation of the use of the calibrating device for medical centrifuge metrology.The device is placed in a medical centrifuge for use, as shown in Figure 2, where Number 41 represents the tube position of the medical centrifuge, Number 42 represents the top cover of the medical centrifuge, and Numbers 43 and 44 represent the rotating shaft and the rotor of the medical centrifuge.Numbers 1, 2, 3, 5, and 6 represent the parts of the device.Number 3 represents the main control unit, which is placed outside the medical centrifuge, and Number 2 represents the laser speed measurement module.Numbers 2 and 3 are connected by the optical fiber.Number 1 represents a wireless temperature collector.Number 6 represents the temperature collect or weight unit, whose weight is consistent with Number 1. Number 5 represents the temperature signal connector, and the signal is transmitted to the main control unit (Number 3) through the signal line.The device can detect medical centrifuges with a rotating speed of 0~30000 r/min, a temperature control range of 0~40℃, and a rotation time of 0~24 h.It is suitable for various types of centrifuges with or without observation holes, operating at low temperatures or normal temperatures.The laser reflection unit (Number 21) is attached to the rotation axis of the centrifuge, Number 22 represents the laser transmitting and receiving end of the device.One end of Number 22 is connected to the main control unit (Number 3), which is extended into the interior of the medical centrifuge through the optical fiber opening gap and attached to the upper edge of the centrifuge top cover (Number 42), thus constituting the laser speed measurement module.Number 1 represents a wireless temperature collector, and the data it collects is transmitted to the inside of the centrifuge through a wireless signal.In addition, the temperature acquisition unit is equipped with a weight unit (Number 6), which is consistent with the wireless temperature collector to ensure smooth rotation of the medical centrifuge.The main control unit (Number 3) is also connected to a clock module to display and calculate centrifuge running time; the collected speed, temperature, and time values are all displayed on the display screen simultaneously through the main control unit.

Figure 3 .
Figure 3. Diagram of main control unit structure.

Figure 6 .
Figure 6.Rotational speed measured at the 15000 r/min measurement point.