Biomedical Engineering Reference
In-Depth Information
8.2.3 Data Acquisition System
The DAQ system contains the necessary hardware to convert the analog signals from
the sensor into digital signals. The following DAQ :NI PCI-6225 from National Instru-
ment Company, Resolution: 16 bits, Analog input channel: 70, Analog output channel: 4,
sampling rate: 250 kS s -1 was used in this experiment.
As previously mentioned, each sensor has two outputs each of which is connected to
a charge amplifier. The output of the charge amplifier is connected to the input channels
of the DAQ through a voltage buffer, which is used to reduce the cross-talk interference
between the input channels in the DAQ. Figure 8.4 shows the electronic diagram of the
setup. The complete experimental setup is shown in Figure 8.5. The tactile sensor is
positioned under a probe. A dynamic load is applied by the shaker, which is achieved by
a power amplifier and a signal generator. The output of the sensor is fed to the connector
box via the charge amplifiers.
The block diagram of the DAQ system is shown in Figure 8.6.
8.2.4 Signal Processing
The processing software, developed in the LabVIEW environment, was specifically
designed for graphical demonstration of the softness of the grasped tissue. Figure 8.7
shows the steps that have been used for the construction of tactile images.
In the first step, the sensing elements on the grasper jaws touch an object. The tactile
data coming from each sensing element are read in the next step. Two input channels in
the DAQ are used to capture data from each sensing element. A filter is used to cancel out
the 60 Hz line noise from these signals. The filtered signals are then used to calculate the
Analog Input (AI) to DAQ
Charge
amplifier
Buffer
Sensor
electrodes
AI+
Instrumentation
amplifier
+
PVDF
film
Bias
resistors
+
Vs
PGIA
+
AI-
Measure
voltage
Vm
Input multiplexers
AI GND
Connector
Figure 8.4 The connections from PVDF to DAQ amplifier. In this figure, only the first channel
is shown. The amplifier is multiplexed between all input channels
 
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