Previous Thread. Next Thread. Print Thread. Copy Link to Clipboard. Share Post on Facebook. Share Post on Twitter. Share Post on Reddit. If you don't inspect Joined: Feb Posts: 9 London, U. Kind regards, Joseph Pickett Henderson Biomedical Ltd, Specialists in the service and repair of centrifuges, heat sealers and other laboratory equipment since www. Kind regards, Joseph Pickett bogia.
Joined: Jan Posts: 6 amman jordan nido Newbie. Ozark Biomedical. Peak Medical Solutions. Wisconsin Biomedical Services, Inc. This site uses cookies. By continuing to browse the site you are agreeing to our use of cookies. Please review our Privacy Policy for more details. I Agree. Site Links. This is the hall sensor. The shaft with the magnet is removed.
Speed control The speed control process happens in the control unit. The control unit does two things. First, it converts the square wave signal from the sensor and compares this with the set speed from the control panel and adjusts the voltage for the motor until the actual speed reaches the set value. The speed signal is also needed for activating the safety lock. As long as the sensor delivers a signal the control unit knows that the centrifuge is spinning and it keeps the lid locked.
Brake When the centrifugation time is over the rotor slows down and comes to a complete stop after a few seconds. This is only possible if the motor is decelerated actively by a brake. The brake is nothing else but a resistor that bypasses the rotating motor.
The rotating motor then acts as a generator and produces energy which is absorbed by the resistor. The 'generator' then runs under heavy load and slows down.
The electrical energy is transformed in the resistor into heat. Because the generated power is quite big, the resistor also has to be big. Indeed it is the biggest resistor inside the centrifuge and it is easy to find. Sometimes it is mounted with some distance on the control board and sometimes somewhere else away from the board where it is better cooled by the surrounding air. A control board with an external brake resistor Timer In the simplest case the timer is just a mechanical clock like an egg timer with an additional switch.
In all other cases the timer is an integral part of the electronic control unit, which might make use of a microprocessor in the most modern centrifuges. Imbalance detector An imbalance sensor detects an unbalanced rotor and lets the motor stop immediately. The sensor is nothing more than a micro switch which is attached close to the shaft. If the load is not balanced the shaft starts to wobble and finally touches the micro switch.
The activated switch gives a signal to the control board which stops the motor. Lid sensor For safety reasons it should not be possible to start the centrifuge when the lid is open.
A micro switch mounted at the lock mechanism detects an open lid and passes this information to the control board. The Solenoid of the safety interlock and the lid switch blue Safety interlock For safety reasons it is also important that the lid is locked during centrifugation. For this purpose a solenoid pushes a metal pin through the latch of the lid.
The solenoid is activated by the control unit. The control unit gets the needed information from the speed sensor. Only when the speed sensor detects a standstill the solenoid gets activated and releases the lid. Please note that in practice this does not happen immediately but after a little delay time. Emergency lid lock release In case of a malfunction or a total failure, all centrifuges have an emergency release for the lid.
How that works is explained in the user manual. But in principle it is a similar procedure as opening a CD or DVD drive of a computer: In a little hole in the housing a pin or screwdriver has to be inserted which pushes back the lock mechanism. Make sure the centrifuge has stopped spinning and the power supply is disconnected before attempting to release the lid lock. Some centrifuges keep the lid locked in case of a power outage. Then the user should know how the lid can be opened manually.
Refrigerator When a centrifuge spins at extremely high speeds, the friction with the surrounding air creates heat. The samples would get warm and that would have negative influences on the samples.
To avoid this, ultra-high speed centrifuges are refrigerated. The cooling unit is similar to the one from a refrigerator and is will not be further discussed here. Maintenance The maintenance procedures described here and in service manuals of the manufacturers are just recommendations and have to be adapted to the situation on site.
The maintenance could be done on a half-year basis. The technician can do a function check, a thorough cleaning and a calibration when it is necessary and when the needed test equipment are available. Preparations Before you start with the maintenance read the user and the service manual of your centrifuge. Document all checks and measurement results in a maintenance report. Check the working place of the centrifuge in the laboratory.
Is it solid, stable and clean? Is the power supply stable? If not, is at least the wall socket protected against spikes and surges? An over voltage protection would be even better. Cleaning during maintenance Clean and disinfect before starting to work on a centrifuge. Spilled samples might be contaminated. Check from the outside Make a visual check of the housing for cracks and for broken-off and missing parts.
Are the rubber feet OK? Check all switches and controls if they function properly. Check the power cord and plug for damages.
Look for burned contacts and loose cables. Is the plug suitable? Replace or shorten the power cord when it is damaged. Pull the cable to check the strain relief. Replace the AC plug when it is of the wrong type and does not match the existing wall socket.
The lid has to close and lock easily. If problems occur, readjust the lid hinges or lock assembly. Check the lid gasket if there is one. Check the sample buckets, their carrier or the rotor for cracks and corrosion. Check the rubber cushions in the buckets if they all are in place.
Check that the rotor is not loose. The centre nut has to be tightened firmly. Test run Make a test run without samples. Listen for any unusual noises. Check the speed adjustment, the timer and the brake function. When stopping the centrifugation, the centrifuge should decelerate. Try to open the lid while the centrifuge is still spinning - it should be not possible. Check the lid security switch.
Try to switch on when the lid is open. This should also not be possible. Check from the inside Make sure you have disconnected the power cable. Take off the unit housing. Look for spilled liquids and corrosion of the metal parts. Take a close look at the circuit board. Examine the electronic components for burns, breaks and leakages. Search the solder side of the board for cold soldering points and disconnections. Check relay contacts for burns. Clean the contacts with a fibre glass brush when the contacts got black.
Motor Check the motor attachment. All screws have to be tight. Usually the motor is mounted in rubber buffers. Check the buffers for ruptures. Rubber buffers also become hard or crumbly after some years. Check the brushes and the commutator for wear. Take out the brushes and check the wear. The surface of the carbon brushes must be smooth and even and should shine silvery.
Replace them if they are less than half of their original length. A motor with new brushes should run for a while without load and at low speed so that the brushes can get shaped. This should be done later after reassembly of the centrifuge. Check the bearings for clearance. Exchange them if necessary. The bearings are in principle always sealed so that they are permanently lubricated.
Lubrication is not needed, they are maintenance free. Lubrication In general lubrication means the use of grease. Apply a small amount of grease and move the joints or bearings. Wipe off unnecessary grease with a cloth afterwards. Use a cloth that you only use for greasy works or better use paper tissues.
Avoid using oil. Oil washes out the grease. Use oil only in exceptional cases or when it is demanded in the service manual. Lubrication areas include lid, hinges, lock mechanism, bucket carrier and sometimes bearings, if they are not sealed. Hand Centrifuges. Small Bench Centrifuges. Mid Bench Centrifuges. Large Bench Centrifuges. Floor Centrifuges. Oil Test and Heated. Continuous Flow. Robotic Centrifuges. Cyto Centrifuges. Centrifugal Evaporators. Cold Traps. PRP Centrifuges. Veterinary Centrifuges.
Chef Centrifuges.
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