Eeg machine working principle and eliminate interference:
Human body tissue cells in spontaneously emerge with a weak electrical activity, the use of electrical activity in the scalp electrodes will be installed on the cell derivation and enlarged by electroencephalograph recorded a waveform, amplitude, frequency and phase of the graphics, curve, is the electroencephalogram (eeg).When brain tissue pathology or functional change, the curve will also corresponding change, thus for clinical diagnosis and treatment of the brain and nervous system diseases, such as the deformity of the central nervous system infection, intracranial tumor and chronic disease, cerebrovascular disease, brain damage and epilepsy, etc.When a neuron by genetic,
Pathology, electrochemical or drugs to stimulate, the balance of the cell membrane is destroyed, produce highly depolarization, action potential can be produced at this moment, the local action potential and will destroy the balance of the next leg of the cell membrane, this a series of repeated recovery and destruction of the cell membrane and biochemical processes, constitute the action potential in the yuan and god on the nerve cell membrane of one-way transmission, creates a eeg signals, the amplitude range of 10-100 mu V, eeg machine is to pick up this is extremely weak brain electrical signal amplification processing, tracing record of apparatus, instruments used to diagnose diseases of the nervous system, its basic principle is as follows:
Input box for metallic shielding box, scalp electrode wire through input box and eeg machine input at the connection,
When the eeg machine on the market today in general in order to reduce the noise in the input box buffer amplifier.Lead selector of different lead and signal channel choice.As weak brain electric signal, amplitude is extremely low, require that eeg machine has high gain, so the eeg machine used more multipolar amplification techniques to achieve its high gain.Also requires a high common-mode rejection ratio.Also has strict requirements for the stability of the power supply, generally in the power supply voltage fluctuation plus or minus 10%, the output voltage change to less than 0.01%, especially supply preamplifier level should be less than 0.5 u V supply voltage fluctuations.The size of the electrode and the skin contact resistance, and electrical record is directly related to the quality, the general contact resistance Should be less than 20 k Ω, if greater than this value, must clean the skin, processing or use better electrode paste electrode, so as to ensure the accuracy of the measurement, so the eeg machine is equipped with electrodes - skin contact impedance measurement device.Telecom amplitude change is bigger, because brain gain control can have more regulation.2 eeg machine interference ruled out because of eeg signals is a very small degree of biological electrical signals, in the signal acquisition, amplification, processing is easy to occur in the process of interference phenomenon, when the brain electrical interference, how to describe the waveform is not smooth, jitter is big, can affect the clinical diagnosis.The interference of eeg machine can be divided into outside and inside the machine.Interference is the main performance calibration waveform is normal, when there is interference in electrical trace.The reason for bad earth, input circuit, the skin, the influence of the electrode contact resistance is too large and the surrounding environment.Machine failure caused by interference more performance for both calibration and brain electrical trace all interference exists, detection can gain switch is placed in a "0", make the preamplifier input to a short road, to see if there is interference, the main reason is bad components ageing, difference amplifier tube symmetry and power filter electric barrier, etc., to eliminate the interference, we should use from outside to inside, from simple to complex method to go on.Around first to see if there are other appliances in the work, as far as possible away from these generates electromagnetic wave devices, and view the box and lead wire electrode and whether patient encounter metallic bedstead or instrument shell, etc., to check whether the grounding of the whole machine is good, but also pay attention to the internal earthing of each module.There was an interference in the test record electroencephalogram (eeg), pay attention to check the signal acquisition amplification processing pathway, check whether the electrodes and scalp is properly connected, electrode box of each socket contact with the lead wire plugs are in good condition.Also check the parts on the circuit board, because there are a lot of the same channel to enlarge, so can use to find the component replacement method, pay attention to check the machine within the power supply filter, voltage regulator circuits, especially to note Filter capacitor, voltage regulator tube, three-terminal voltage regulator block, etc.Heart eeg machine is in use and interference in the process of verification and eliminate heart eeg machine is widely used for hospital diagnosis inspection equipment.But in the use of the diagnosis and verification process, cardio-cerebral electric figure machine communication interference is one of the most common and most pressing problem.The generation of interference phenomenon directly affect the accuracy of the eeg machine wave heart, make the recorder described in the graphic mutation amplitude of waveform, which directly affect the doctor's diagnosis.
1. The leakage current interference.
Heart of eeg in the diagnosis of indoor ac power possible leakage current, the alternating current through the verification instrument, ground, the body and other adverse insulators and instrument grounding line form a loop, which is formed on the waveform in eeg recorder described modulation interference.
2. Space interference.
Beware of eeg machine near has a large power transformer, motor, and using high power device, alternating current electromagnetic field in lines, radiation absorption is formed on the shell and the modulation and so on.Is due to the magnetic flux leakage exists, its surrounding will produce larger interference, magnetic field effect on mind electroencephalographic lead wire, will produce induced current, affect the accuracy of heart record sheet value of the eeg machine.
