Combined with the characteristics of EEG clinical examination, some special requirements for the whole machine are also put forward. Due to the EEG signal generally consists of a plurality of electrode tip site from the unified leads, leading out electrode line is if the trunk and root, so often used the middle junction box, also known as the input box. The lead outlet is directly connected with the input box, and the brain electrical signal is sent to the EEG machine by the input of the input box. Because lead is more, and to observe the symmetry of the electric field distribution and instantaneous changes, the general requirements for synchronous recording, so there must be a multi-channel amplifier and recorder at the same time, the common general 8, 16, 32 lead, etc.. Some machines also attach a heart and a sign lead. Therefore, the EEG machine to record the paper to be much wider, which puts forward higher requirements on the paper motor, general motor output power should be more than 1.5W, many amplifiers and recorders in a fault will make the whole record is affected. In order to facilitate the analysis of the mutual relations between the signal waveforms of the lead EEG signals, the clock signal and the calibration signal are set up in the machine.
The EEG machine should also be equipped with an electrode skin contact resistance measurement device to measure the contact resistance, suggesting that the improvement measures to ensure good contact. General contact resistance should be less than 20K, if more than this value, it is necessary to clean the skin, the treatment of the electrode and the use of better electrode paste. In order to ensure the personal safety and measurement accuracy, the measurement of power supply should be used to exchange constant current source.
Because of the large variation of the amplitude of EEG signal, it is required that the gain control can be used in many kinds of large scale and fine adjustment. Because of the difference of the frequency of EEG signal, in order to adapt to the needs of different frequency waveform recording, the amplifier should have a variety of different frequency of low cut and high cut filter, at any time can be converted. Similarly, the time constant, the speed of the paper should be more than the choice of multi file. More advanced EEG machine, the use of microprocessor control operation of the state, along with the signal of the record, in each of the guide wave can automatically print out their work parameters, and some can directly print out the value, and some can print out their encoding tag, this tag to skilled operator, as long as a little thinking can be directly decoded by the brain.
EEG is electrode to collect evacuation to the input box, then after the lead selector and amplifier sends to the recorder for recording. The modern EEG machine is used to control the operation of CPU, the operation process is accomplished by the monitoring program stored in ROM.
1 input box
Scalp electrode wire generally do not directly and electroencephalograph input terminal connection, but through the input box and the host computer is connected, the input box is a metal shielding box, an electrode jack, including more than 20 brain electrode jacks, and connected to Jack, socket etc., external jack can be used for recording EEG, EMG, EOG, induced respiratory wave and power generation. In the case of a buffer amplifier, some are also equipped with an electrode impedance measuring device.
2 lead selector
Usually a node switch array, a set of nodes from the CPU instruction can be connected to the corresponding signal from the electrode to the amplifier input. EEG machine can provide fixed lead and free lead programming.
3 amplifier
The amplifier is composed of a multi-stage amplifier, and the other is the time constant, high frequency filter, sensitivity control, AC interference suppression and other circuits.
4 recorder
The EEG machine of pen type recorder, the ink pen.
5 control section
The keyboard scan circuit is mainly used to generate the corresponding key code, so that the CPU for the corresponding operation, these operations include the selection of lead and programming, calibration, optical stimulation, reference electrode selection, and so on.
6.CPU part
Modern EEG machine has a lot of microcomputer control, such as Japan's 7300 series of photoelectric, the use of Z80 chip, plus 48KROM, 8KRAM and 8255 chip, etc..