44
Single Channel ECG Test System | User Manual
•
Open switch S2 (input impedance test)
•
Measure the resistance between RA and LL
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
(100kΩ:100Ω)
1000:1 ±0.2%
Resistance values are specified as 100kΩ 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 10mVpp 0.1Hz square wave to
output RA
•
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 10Vpp).
•
Repeat this measurement at the output
between RA and LL (nominally 10mV)
•
Calculate the ratio and confirm it is 1000:1
±0.2%
Output
voltage
Setting ±1%
Method:
•
Set up 0.5mVpp 0.1Hz square wave,
output to RA
•
Measure the peak to peak output between
RA and LL, using the Fluke 8845A or
equivalent, record this as output mVpp
•
Repeat for 1, 2, 5, and 10mVpp
•
Confirm all values are within 1% or 5µV of
the set value
Note: the Fluke 8845A has suitable accuracy at
10mVpp but has borderline accuracy at 1mVpp
and lower. An alternate method is to measure
the output at BNC2 and then use the divider
ratio above.
DC offset
(fixed
±300mV)
300mV ±1%
Method:
•
Set the equipment to “Off”
•
300mV
