References

24 Electrophysiology and Phototropism 357
L
I
G
H
T
b
PC
Ni 6052 DAQ Card
LabView
Sigma Plot
LIGHT
SOIL
a
Ag/AgCl Electrode
Ag/AgCl Electrode
Ag/AgCl Electrode
Ag/AgCl Electrode
FARADAY CAGE
Shielded
Cable
NI SC-2040
Simultaneous
Sample and
Hold
Fig.24.1. Experimental setup for measuring electrical signals in green plants
well-known methods such as electromyograms (EMG), electrocardiograms
(EKG) and electroencephalograms (EEG) are based upon measurements of
the summed bioelectrical activity in large groups of cells.
Figure 24.1 shows the experimental setup for bioelectrochemical measurements
inside a Faraday cage mounted on a vibration-stabilized table.
An IBM-compatible microcomputer with a NI 6052E DAQ multi I/O plugin
data acquisition board (National Instruments) was interfaced through
a NI SC-2040 simultaneous sample and hold (National Instruments). The
multifunction NI 6052E data acquisition board provides a high resolution
and a wide gain range and supports continuous, high-speed data acquisition.
Single channels can be sampled at any gain up to 333,000 samples per
second. Measuring signals were recorded using LabView (National Instruments)
software.
A fundamental rule of sampled data systems is that the input signal must
be sampled at a rate greater than twice the highest-frequency component
in the signal. This is known as the Shannon sampling theorem, and the
critical sampling rate is called the Nyquist rate. Stated as a formula, it says
that fs/2 >fa, wherefs is the sampling frequency and fa is the maximum
frequency of the signal being sampled. Violation of the Nyquist criterion is