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Document number 291945 V5
Place the two sensors on the seat back approximately to the left and right of the spine and
mid back.
Virtual instrument:
If using the soft virtual instrument then:
•
Select “Differential A-B” from the channel selection.
•
Set filters
•
High Pass
“IN”
8.0
Hz
•
Comb
“IN”
6
– 25 Hz
•
Low Pass
“IN”
40.0
Hz
•
Voltage scale:
10mV or 50mV
•
Time base: 0.5s/div
Start the oscillogram. Adjust the gain of the DRL circuit using the gain control on the back
plane of the Control/Interface box. If the gain is too low the ECG signal is lost in the common
mode signal and no net signal can be retrieved. If the gain is too high the system becomes
unstable. There will be an optimum gain when the differential ECG signal is produced. The
soft oscilloscope gain may need to be increased to observe the signal. The position of the
sensors may need to be adjusted to obtain the best signal.
Background
EPIC is a capacitive sensor and so does not rely on ohmic contact to the body for measuring
bio-electrical signals. It therefore has the ability to measure ECG without direct skin contact.
Signals measured on the human body always include a large amount of noise, the major
component of this being 50 or 60 Hz power line noise capacitively coupled to the body from
the mains electricity supply. Measurements such as ECG depend on being able to extract
the small electrophysiological signals from the much larger noise signals.
When using EPIC in “contact mode” for ECG measurement, the subject touches both the
capacitive electrode surface and some metal at the system ground directly with the skin.
This ground reference allows filtering and differential amplification of signals from two
sensors to be effective in removing the mains frequency noise, leaving a high quality ECG
signal.
