Combining with the characteristics of eeg clinical examination, for the machine also put forward some special requirements.Because eeg signals by several commonly electrode from the unified position, head of electrode wire has a number of root, so often use intermediate junction box, also known as the input box.Electrode lead wire connected to the input box directly, through the input box again lead to brain electrical signal to the eeg machine.Because more lead, and to observe the cerebral electric field distribution is symmetrical and instantaneous change, general requirements synchronized record, so there must be a multichannel amplifier and recorder work at the same time, the common general has 8, 16, 32, guidance, etc.Some machines have attached a lead ecg and a token.Therefore eeg machine has a much wider recording paper, it puts forward higher requirements on paper feed motor, general motor output power should be above 1.5 W, a pilot in many amplifier and recorder down will make the whole record.In addition to facilitate the analysis of the lead eeg waveform is contact with each other, the machine set up within the clock signal and calibration signals.
Eeg machine should also be equipped with electrodes - skin contact resistance measurement device, to measure contact resistance, prompt improvement measures are taken to ensure good contact.Contact resistance should be less than 20 k Ω commonly, if more than this value, you must clean the skin, electrode and electrode paste using better.In order to ensure the personal safety and measuring accurately, measuring power ac constant current source should be adopted.
By changes in brain electrical signal amplitude is large, so the gain control can have more coarse and fine adjustment, also set a variety of calibration voltage amplitude.Because the eeg changes the frequency difference is significant, in order to adapt to the needs of the various frequency waveform recording, amplifier should have different frequency of low cut and high cut filter, can convert any time.Also, the time constant and the feeding speed should have more choice.More advanced eeg machine, using microprocessor control system operation state, as the signal recording, next to the waveform guide can automatically print out the working parameters of each amplifier and recorder, some can directly print out the values, some can print out their coding standard, this kind of tag for skilled operators, with a little thought can be decoded directly through the brain.
Brain electrical signals sent to the input box, after being electrode pick up then after lead selector and amplifier to eeg recorder.Modern CPU eeg machine commonly used control the operations, the operation process done by stored in ROM the
monitoring program.
1. The input box
Head skin electrode wire is generally not directly connected to the eeg machine input facies, but through the input box connected to the host, the input box for metallic shielding box, electrode on the jack, including more than 20 brain electrode insert, and grounding plug hole, external socket, external socket can be used in eeg, eeg, emg, eye induced electricity, electricity, respiratory wave and so on.Box inside the buffer amplifier, sometimes with the electrode impedance measurement device.
2. Lead selector
Switch array, is usually a node from the CPU instructions through a set of nodes can send corresponding biological electrical signals from the electrode to the amplifier input.Eeg machine can provide fixed lead selection and lead free programming.
3. The amplifier
Consists of multistage amplifier amplifying circuit, and also including time constant transformation, high frequency filter, sensitivity control, communication interference suppression circuit, etc.
4. The recorder
At present, a lot of eeg machine pen recorder, most of them adopt ink pen.
5. The control part
Mainly the keyboard scanning circuit, used to generate the corresponding key code, the CPU to make corresponding operation, these operations including the selection of lead and programming, calibration or eeg, light stimulus, the selection of reference electrode and so on.
6. The CPU part
There are a lot of modern electroencephalograph is microcomputer control, such as Japan photoelectric 7300 series, use Z80 chip, plus 48 krom, 8 kram and 8255 chip, etc.
