
MAKING YOUR OWN ADAPTER OR ACTIVE PROBE Page 61
C
YBER
A
MP
380, COPYRIGHT MARCH 2002, AXON INSTRUMENTS, INC.
Current Probes
Photodiode Amplifier
1
U
INPUT
R
100 M
Ω
C1
0.1
C2
0.1
100 mV/nA
ANALOG GROUND ( 10 )
15 V ( 8 )
INPUT ( 2 )
15 V ( 15 )
CURRENT
Figure 26. Current-to-voltage converter. The output voltage of U1 is proportional to -R1 times the input
current (I). Since this inverse output is connected to the negative input of the CyberAmp, the output of the
CyberAmp will be positive for positive values of I. For R1 = 100 MΩ, the sensitivity is 100 mV/nA. Different
values of R1 can be used for different sensitivities. A FET input op amp should be used. The dotted line
shows how a photodiode can be connected.
Wheatstone Bridge Strain Gauge Circuits
R
R
R
R
5.000 V
4
INPUT
1
INPUT
2
ANALOG GROUND
10
Figure 27. Standard connections for a Wheatstone bridge strain gauge used for pressure, force, strain or
other measurements. For example, if the gauge manufacturer quotes a sensitivity of 5 µV/V/mmHg, then the
sensitivity of the gauge when connected to a CyberAmp is 25 µV/mmHg. The resistance (R) of each arm of
the gauge is often 350 Ω, but higher or lower values are possible. If substantially lower values are used, the
user should make sure that the total current drawn by all CyberAmp channels from the +5.000 V excitation
supply does not exceed the specified rating.
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