
Page 36 PRINCIPLES OF OPERATION
C
YBER
A
MP
380, COPYRIGHT MARCH 2002, AXON INSTRUMENTS, INC.
Box 1
1) From Equation 2;
RM
V
Gain V
e
=
−
1
0
0
Ω
2) For low values of R
e
, the 1 V
p-p
square wave drives an approximately 1 µA
p-p
current into the electrode. Thus the electrode resistance can be approximately
determined from:
RM
V
Gain
Rk
ee
=<150
0
ΩΩ
Giving R
e
= 1 kΩ for each mV at V
in
.
Figure 16. These graphs can be used to determine the electrode resistance measured during Electrode Test.
The solid line in Graph A represents equation 1 in the text. It reaches a maximum error of about 5% for
electrode resistances of 50 kΩ. The dotted line represents equation 2 and is accurate for all electrode values.
Graph B shows equation 2 over an extended range. These graphs assume that the CyberAmp is set for x1 total
gain, with one input grounded.
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