CENTRIFUGAL MACHINE

A centered function is a machine that rotates a sample to centrifugally separate its components or phases (in general, a solid and a liquid), depending on its density [1]. There are different types of centrifuges, such as low speed centrifuges, centrifuges for micro hematocrits, and ultracentrifuges, the latter type is generally used for the separation of proteins. But each of them has different speeds [2]:

• Centrifugal macro that goes from 2,000 and 6,000 R.P.M.

• Micro centrifuges between 10,000 and 18,000 R.P.M.

• Ultracentrifuges ranging from 20,000 and 75,000 R.P.M

COMPONENTS

Cabinet. It is the space in which the centrifugation process is carried out. Inside it rotates the rotor or spider.

Rotor. Also known as a spider, it is the section in which the sample holders are placed and the one that will move when the equipment is put into operation.

Sample holder. The sample holders are those containers where the samples are placed for centrifugation. The size of the sample holders is variable and depends on the design and function of the centrifuge.

Base. The base is the part that supports the rest of the equipment and usually contains the controls to operate the centrifuge. Generally, the base is built with heavy materials and has a fixing system to the surfaces on which the equipment is placed, this with the purpose of providing greater stability.

Front. The lid is a component that prevents access to the samples while the equipment is in operation. Most centrifuge models incorporate a padlock on their cover that is activated automatically so that the equipment can not be opened when it is in operation.

Ignition switch. With this switch, the energy supply to the centrifuge is controlled. It integrates tools so that the user can configure the operation mode of the equipment.

Time control. With this controller, the centrifugation time of the samples is determined. In addition, it allows to visualize the elapsed or pending time for the selected process.

Tachometer. The tachometer shows the speed at which the spin is being performed by measuring it in revolutions per minute.

Brake. This element is not present in all the equipment, but those that present it allow the user to accelerate the process of stopping the operation of the centrifuge. It is particularly useful in emergency situations and the way it works depends on the manufacturer, which is why it is recommended to verify that the centrifuge integrates it and follow the instructions of use provided by the manufacturer when using this function [3].

Pulse width modulation (PWM)

Width or pulse modulation (or in English pulse width modulation PWM) is a type of voltage signal for sending information. This type of signals is very similar in digital circuits that need an analog signal [4].

Encoder

Encoders for most used DC electric motors used in the mining industry, transport (trains) and wind turbine generators. Its function is to convert the mechanical movement (turns of the axis) into digital pulses or similar that can be interpreted by a motion controller [5].

Functioning

As the axis rotates, the infrared emitter emits light that is received by the optical sensor (or photo-transistor) generating the digital pulses as the light crosses through the disc or is blocked in different sections of the disc [5].

Materials:

Now we show you how to build a Centrigual machine, but first, you must have this materials to do it.

What are you waiting for?

SCHEMATIC DRAWING

Here you can find the shematic circuit to build the external prototype. these selected pins are the same that we used with the code.

Careful to confuse them! :)

Now, once the circuit was built, we will proceed to explain the code

its a little bit longer, but we'll explain it to you below

First of all, we have to call the pins that we want to use for Keypad and LCD, for that reason, we call two libraries of Arduino that help us to use these external elements, These libraries are Keipad.h and LiquidCrystal.h. After we can then we can assign the pins.

Now we created some variables that help us to keep the time,and frecuency of PWM, then in the Void setup function We attach to each pin as input or output.

Now, as you can see, we create a function to put a PWM by user with the leypad and detect the RPMs with a characterization of the sensor of a horseshoe.

here, we have another function to set the time for centrifugate the sample. like last function, we use the kaeypad to set the time by the user, then we keep it in variable tt.

this is the last part of code in Arduino, is the main code to aplly all variable and activate the centrifughal machine. We detect the RPM detected by sensor and show it in LCD, also we put a Buzzer like visual alarm when the door of centrifugal machine is open during centrifugation.

Results and analysis of resulFor the characterization of the engine were taken frequency values displayed on the oscilloscope which was connected to the output of the horseshoe sensor that was also connected to the pin 2 of the Arduino. By code and using the matrix keyboard, the PWM value corresponding to each frequency obtained is digitized. Of these values a graph was obtained, the respective regression was carried out and its equation was obtained to use it in the proposed code.

To obtain RPM was multiplied each of the values of frequency by 60, this value corresponds to the seconds in one minute. After doing this calculation, it generated a graph of relation RPM vs PWM, to which the respective regression was applied, its equation was obtained and this one was used in the code. All this to associate the value of RPM with PWM and that, when typing with matrix keyboard rpm, put in operation and motor and start the spin process.

The results show that in the system designed for the implementation of a centrifuge, the power stage for the engine, the horseshoe sensor and its conditioning, and also, the program developed and executed in Arduino, worked properly, and When the RPM and the spin time have been digitized by keyboard, the motor was activated and the spin stage began, and each typed value was visualized in LCD. Additionally, the program triggered an alarm when the spin process was interrupted and the engine stopped working.

Experimental Analysis

This practice of centrifuge was made based on the horseshoe sensor and a DC motor in which a black sheet was placed at a point of the motor, this sheet, when passing through the sensor counted a pulse after its passage. With this system was able to obtain the frequency displayed in oscilloscope and from this calculate the value of RPM. This system was characterized by the use of PWM which allowed us to activate the engine for the start of the spin stage.

A code was developed in Arduino in which the matrix keyboard was programmed which allowed us to enter both RPM and spin time. Also, a power stage was implemented for the engine which, by typing the RPM related to the PWM value, activated the engine, while these values were not digitized, the engine did not enter the spin stage. The alarm implemented, warning the suspension of the spin process, this happens when the door opens.

GLOSARY

Coil: It is the winding of a conductor wire around a solid or hollow cylinder, this and due to the special geometry obtains important magnetic characteristics.

Blocking: It is the means that prevents the partial or total change of the operation.

Sample holder: Support device that allows and facilitates the analysis of a sample.

Axis: An axis is a constructive element designed to guide the rotation movement of a part of a set of parts, such as a wheel or a gear.

Buzzer: Electric bell that emits a continuous and deaf buzz.

Horseshoe.: Which is U-shaped, like this piece of iron.

REFERENCES

[1] "THAT IS A CENTRIFUGE", Equiposylaboratorio.com, 2018. [Online]. Available: https://www.equiposylaboratorio.com/sitio/contenidos_mo.php?it=2251.

[2] Q. General, L. Materia, T. Atomic, Q. Organic, Á. Bases, C. Chemistry, C. Chemists, E. Chemist, Periodic L., Environmental Q., Living Q., Nuclear Q., R. Chemicals, L. Chemical, M. Chemical, P. Laboratory, Q. Function, S. Auxilios, M. sitio and T. Químico, "Centrifuge of Laboratory» TP - Chemical Laboratory ", TP - Chemical Laboratory, 2018. [Online]. Available: https://www.tplaboratorioquimico.com/laboratorio-quimico/materiales-e-instrumentos-de-un-laboratorio-quimico/centrifuga-de-laboratorio.html.

[3] E. marketing, "Components of centrifuges for laboratory | El Crisol", El Crisol, 2018. [Online]. Available: http://elcrisol.com.mx/componentes-las-centrifugas-para-laboratorio/.

[4] "Modulación por ancho de pulso (PWM)", Arduino UTFSM, 2018. [Online]. Available: http://www.arduino.utfsm.cl/modulacion-por-ancho-de-pulso-pwm/.

[5] "¿Qué es un encoder? ¿Cómo funciona? Y tipos de encoder que existen", My Blog, 2018. [Online]. Available: http://www.abm-industrial.com/2013/02/07/que-es-un-encoder/.