Single Channel EEG Test System | User Manual
18
2.7.1 Calibration procedure
Parameter
Nominal
value,
tolerance
Method
Input
impedance
resistor
620kΩ±1%
This can be measured as follows:
•
Set Main function to “Off”
•
Set output to ch1
•
Uncheck “620KΩ/4.7nF”
Measure the resistance between ch1 and ch2
Input
impedance
capacitance
4.7nF±5%
Measure as for the 620kΩ above, using a
capacitance meter at 1kHz. Note: there is
about 100pF stray capacitance in the circuit
which is included in the measurement.
However, even with this the measured result
is within the limit.
Precision
divider ratio
(50
kΩ:100Ω)
500:1 ±0.1%
Resistance values are specified as 5
0kΩ and
100Ω ± 0.1%, but these cannot be verified
once in circuit. An alternate method is used to
verify the accurate ratio:
•
Set up a 2mVpp 0.1Hz square wave to
output ch1
•
Using the Fluke 8845A or equivalent
precision meter, measure and record
the peak to peak voltage at BNC2 by
zeroing during the negative cycle, and
measuring at the positive cycle
(nominally 1Vpp).
•
Repeat this measurement at the
output between ch1 and ch2
(nominally 2mV)
Calculate the ratio and confirm it is 500:1
±0.2%
Output
voltage
Setting ±1%
Method:
•
Set up 0.2mVpp 0.1Hz square wave,
output to ch1
•
Measure the peak to peak output
between ch1 and ch2, using the Fluke
8845A or equivalent, record this as
output mVpp
•
Repeat for 0.4, 0.5, 0.8, 1, 1.5 and
2mVpp