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GP Amp Operation
The GP Amp is essentially an extension of the PowerLab’s analog
input. The GP Amp provides:
• a ±10 V DC excitation source that can power transducers requiring
such excitation
• the additional amplification necessary to deal with the low signal
outputs of most transducers
• high-impedance differential input
• additional programmable filtering to remove unwanted signal
frequencies
• digitally controlled zeroing circuitry for offset removal.
The internal functions of the GP Amp are controlled from the
PowerLab through the I 2 C bus, which also supplies power to the
GP Amp. The front-end sends the signal to an analog input channel of
the PowerLab via a BNC-to-BNC cable. The overall operation of the
GP Amp can be better understood by referring to Figure A–1.
Figure A–1
Block diagram of the
GP Amp
AC/DC
coupling
Gain
control
Filter
control
Signal
input
+
_
×1 /
× 10/
× 100
10 kHz
100 Hz
10 Hz
Signal analog
Output output
Transducer
power
Excitation
voltage adjust
On-line
indicator
Excitation
driver
DC offset
control
VRef
12-bit
DAC
1 Hz
2 2
I C
control
interface
+
power
supply
I 2 C I C
output Output
2
I 2 C I C
Input input
The input stage is a high-impedance differential instrumentation
amplifier. The amplifier provides additional signal amplification.
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GP Amp Owner’s Guide