 |
Instrutech ITC-18 Data Acquisition Interface
The ITC-18 is the second-generation low-noise
16-bit computer interface from Instrutech Corporation. The
ITC-18 offers unsurpassed
capability while retaining all of the exceptional features
of its predecessor, the ITC-16. The ITC-18 provides a major
improvement in the quality of acquired data, making measurements
that would otherwise not be possible.
Hardware Configuration
The ITC-18 is an external rack-mountable data acquisition
unit that is attached to the computer using a dedicated
host interface
card. This configuration offers major advantages over traditional
data acquisition designs. Most data acquisition devices
are printed circuit boards installed directly into the
computer.
The interior of a computer is an electrically noisy environment
that will dramatically affect the noise performance of
high speed D/A and A/D converters. Mounting all of the
analog
electronic components in an external box provides the most
effective means of shielding the analog signal from this
noise.
The PCI-18, the ITC-18 PCI host interface card is compatible
with all PCI 2.0 compliant computers. Moving the ITC-18 from
one PCI computer platform to another is a simple matter of
relocating the host interface card, and installing compatible
software. For non-PCI compliant computers we offer the AT-18
for ISA bus, and the MAC-18 for the NUBUS. All three computer
plug-in cards, the PCI-18, AT-18 and MAC-18, connect to the
same ITC-18 interface. Utilizing the same hardware when changing
computer platforms provides a cost effective upgrade path to
newer computer technologies without sacrificing your initial
investment. Optical Isolation
The analog electronics of the ITC-18
are optically isolated from the digital circuitry of the
computer. This provides
complete electrical isolation between the computer and
the equipment making your measurements. Computers contain
digital
electronics that switch at high speed, producing large
electrical transients. The computer ground functions as
the return path
for these transients, resulting in substantial high frequency
ground noise. The ITC-18 has a completely separate analog
ground that is isolated from the computer ground. With
the ITC-18 computer ground noise is not coupled into the
measurement. Optical Isolation is essential if low-noise analog outputs
are desired.
The optical isolation of the ITC-18 brings with it another
benefit that simplifies complex measurement systems. Since
the analog inputs and outputs of the ITC-18 float with respect
to power ground, the ITC-18 and the computer are not a source
of ground loop problems.
FIFO Memory
The ITC-18 is now supplied with a large
1024 kilosample FIFO memory for input and output data. The
ITC-18 allows data
acquisition to be performed independent of the activity
of the host computer.
A large FIFO memory allows uninterrupted continuous high-speed
acquisition with today's multitasking operating systems. Specialized Applications
The ITC-18 uses programmable gate
arrays that allow the internal hardware to be altered
for specialized applications. One
available application is the Artificial Synapse Dynamic
Clamp. The clamped
cell is connected to an A/D input via a Voltage Clamp
amplifier. The stimulus is computed, based on voltage
measured from
the cell, lookup tables for excitation, inhibition and
conductance values and other parameters. This stimulus
is applied to
the
cell via the current input of the Voltage Clamp amplifier. The ITC-18 implements Dynamic Clamp in hardware rather
than in software. In this Dynamic Clamp configuration the
ITC-18
samples four co-phase A/D channels at 50 kHz (20 us), performs
the necessary calculations and drives the outputs. All
calculations are done within one sample clock, resulting
in an input to
output delay of only 20 us.
Analog I/O
A unique design characteristic of the ITC-18
is the synchronization of all analog and digital signals. All
inputs and outputs
are updated simultaneously. Most data acquisition devices
on the
market do not do this. They sample multiple channels
by using a multiplexer. This means that there is a time
delay
between
the samples from each channel. This makes timing correlation
measurements difficult. The ITC-18 does not stop with
this capability. An external clock option allows for
precise synchronization of multiple ITC-18 interfaces or our
DVP-32
Digital Video
Processor. This feature allows for the simultaneous
sampling
of more than
8 channels (using multiple ITC-18 interfaces) or the
synchronization of video images with your analog data
(using the DVP-32
Digital Video Processor). The ITC-18 provides eight analog input channels. Each
input channel uses an 18-bit A/D converter preceded by
a programmable
gain stage. Each A/D input can be programmed with a full-scale
range of +1, +2, +5, or +10 Volts. This gain stage reduces
the need for external signal amplifiers before the ITC-18.
Using separate A/D converters for each analog input channel
also has advantages. One benefit gained by using separate
A/D converters is reduced crosstalk between channels.
The same
multiplexer mentioned in the previous paragraph, is the
source of another disadvantage. It is a single point
where all of
the analog input signals connect. This point, where the
analog signals come together, can introduce cross coupling
between
the signals. The amount of crosstalk will vary based
on frequency and amplitude. High-frequency signals show
the
greatest coupling
into other channels while large amplitude signals will
also couple into smaller signals. The ITC-18 has no measurable
cross talk between channels.
The ITC-18 provides four 18-bit instrumentation
grade D/A converters featuring high accuracy with less than
1 bit
(~300 mV) of noise.
This extremely low noise allows for the observation of
least significant bit transitions. The D/A circuitry
used in the
ITC-18 is temperature stabilized and "De-glitched" for
ideal performance. A typical D/A circuit will have a
large glitch energy around zero and major bit transitions,
the ITC-18's
D/A converters are free from this artifact.
The ITC-18 uses a "sequence RAM" to
control the sampling order of both the analog and digital
channels. This provides
the ability to update individual channels at different
rates. This arrangement optimizes the acquisition of signals
with
dissimilar bandwidth.
This architecture makes the ITC-18 particularly important
when making measurements using high-frequency signal
sources, multiple
signal sources with large differences in amplitude
between them or when analyzing multiple signals for timing
correlation.
Digital I/O
The ITC-18 provides sixteen digital inputs,
thirty-two digital outputs, seven sequence RAM trigger outputs
and fourteen
asynchronous non-isolated digital outputs. The
digital
input channels feature
level sensitive or latched modes. For maximum versatility
the inputs can be inverted, allowing rising or
falling edge triggering.
Thirty-two digital output channels in two banks
of sixteen, with fourteen channels paralleled with current
sink circuitry
for driving perfusion valves, solenoids, or other
devices directly. Seven programmable trigger outputs
for triggering
from any
location in the scanning sequence RAM and fourteen
asynchronous auxiliary digital outputs that can
be updated at any
time regardless of the ITC-18's acquisition state
are available. Software
Support
The ITC-18 has extensive software
support. Software drivers are available for Windows 3.x, Windows
95/98, Windows NT, Windows 2000, Windows XP, MacOS classic,
MacOS X, Linux, National Instruments LabView, and for Wavemetrics
IGOR Pro (XOP's). Software packages that support the ITC-18
are PatchMaster, Pulse, X-Chart and TIDA from Heka Elektronik,
Acquire and Device Access from Bruxton Corporation, AxoGraph
from Axon Instruments and PulseControl from Dr. Bookman. Many
custom applications have also been written for the ITC-18.
Please contact us to discuss any specialized applications
that you may have.
|
|
• All
synchronous analog and digital channels are optically isolated
• Eight
simultaneously sampling differential analog input channels
• Eight
18 bit 200 kHz A/D converters
• 200
kHz to 12 Hz sampling in 1.25 mS steps (200 kHz max aggregate)
• Programmable
input gain: 1x, 2x, 5x, 10x
• Analog
input range: + 10.24 volts
• Four
pseudo differential analog output channels
• Four
18 bit instrumentation grade D/A converters
• Analog
output range: + 10.24 volts
• Sixteen
synchronous digital input channels
• Thirty-two
synchronous digital output channels, fourteen with current
sink
• Sixteen
asynchronous digital output channels
• Large
1024 kilosample FIFO now included at no additional cost
• PCI,
ISA, and NUBUS host interface cards available
• Easy
installation, no IRQ or DMA channel settings
• Compatible
with Windows9x, NT, 2000, XP, MacOS classic and X, LabView
for Windows, MatLab
and Linux |
|
