SOMATICS, LLC
REV: 3.1 09/15/2015
15
4.
THEORY OF OPERATION
General Description
The internal circuitry is contained on 4 PC boards and one printer module. These are:
4.1. Analog board
4.2. Control board
4.3. Power/ Output board
4.4. Display board
4.5. Printer module
See fig. 4.1 for Interconnection diagram.
4.1.
Analog board
The analog board consists of EEG channel 1 and 2 amplifiers, EEG/EMG channel 3
amplifier, EEG/ECG channel 4 amplifier. isolation power supply, sound circuitry,
impedance circuitry, output measurement circuitry, 13 bit serial A/D, optical isolators,
microcontroller to move data between the main CPU and A/D, and two output protection
monitor microcontrollers.
The analog channels consist of input overvoltage protection circuitry connected to an
instrumentation amps. The signal is then amplified with two stages of amplification for
total of x4000. The next stage is a three pole low pass filter set at 50 Hz as well as level
shifter for the A/D.
A/D is a 13 bit serial A/D with 8 channel input. Channels 1-4 are the biological signals
from the patient, channels 5-7 are impedance and output measurement channels. The
digital data from and to the A/D are isolated with a high speed optical isolators. An
isolated power supply provided ±5 V from the 5V power.
The impedance measurement is derived by injecting 6
µ
amp current into the treatment
electrodes and using an isolated differential amplifier to amplify the difference voltage
which is proportional to the impedance of the electrodes. A safety relay is added in the
ECT path. This relay is controlled by the treat switch and one of the two safety monitors
and is a backup safety system for patient disconnect in case of primary failure.
The output current and voltage measurements are achieved by using two isolating
transformers that isolate the signals from the output and which are then amplified and
coupled to the A/D.
The microcontroller is connected to the main bus via a slave port and is used to serially
control the A/D as well as to pass data from the A/D. It also generates the impedance
source signal and the EEG sound signal as well as the warning sounds.
The sound system consists of a 3" speaker and a volume potentiometer mounted on the
rear panel. The amplifier sums up the various sources of warning signals as well as the
EEG modulated sound. The EEG sound is the only one that can be controlled by the
