natus Grass S88X, Руководство пользователя и обслуживания

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4-22
Chapter 4
Description of Circuits
o
utPut
c
ircuit
The S88X is driven by a Digital Signal Processor (DSP). To create the output
waveforms the DSP writes 16-bit binary values to a Digital to Analog
Converter (DAC). The DAC puts out a voltage that corresponds to each
value. The DSP can write a new value to the DAC every 10 µs. By varying
the binary value written to the DAC the DSP can vary the output over time
to produce the desired waveform. The DAC output is then multiplied by a
factor of 10 and sent to the output of the S88X.
The output of each amplifier is monitored to detect an over-temperature
condition. The DSP monitors the output of this circuit to detect the over-
temperature condition.
At initialization, the output circuits are disconnected from the output of
the S88X. This prevents the output from generating outputs inadvertently.
When the DSP gets to a particular point in the code, it connects the output
circuits to the output of the S88X.
The output circuit also contains a low power section that takes as an input
the amplified signals and puts out a composite signal used to monitor the
output.
s1 & s2 o
utPut
a
mPlitude
The S88X S1 and S2 outputs are low impedance constant voltage outputs.
Both outputs are current limited and short circuit protected. The maximum
output current from each output is 1.1 amperes. The voltage can be varied
from 0.25 to 24 volts. Accuracy is 0.1% of reading ±1 mV.
Amplitude is set by the OUTPUT AMPLITUDE thumbwheel dial. The output
can swing b24 volts and –12 volts maximum. For monophasic and
twin pulses, the output is 24 volts maximum. When in the biphasic mode,
the output is between –12 volts and +12 volts.
The available high output current can be used for special applications.
Field stimulation of isolated tissue in tissue baths can be achieved. Vessel
rings, strips of muscle and other preparations can be stimulated using
field stimulation techniques. These setups typically utilize parallel plate
electrodes submersed in various solutions for various drug testing and
experimentation.