The HEKA InstruTECH ITC-18, is the second generation low-noise 16-bit data acquisition interface designed by InstruTECH. 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. This configuration offers major advantages over traditional data acquisition designs. One advantage is noise performance. 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.
Another advantage is the capability to use the analog front end (ITC-18 rack unit) with a variety of host interfaces. Moving the ITC-18 from one computer platform to another is a simple matter of using the appropriate host interface, and installing compatible software. Utilizing the same hardware when changing computer platforms provides a cost effective upgrade path to newer computer technologies without sacrificing your initial investment. Since the ITC-18’s initial inception we have designed host adapters to interface to various computer bus architectures (i.e. ISA, NUBUS, PCI, and USB 2.0).
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 measuring equipment. 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.
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 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 V. 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 other 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 µV) 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 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. ITC-18’s that use a USB-18 host interface have an additional sixteen asynchronous non-isolated digital inputs and outputs.
FIFO Memory
The ITC-18 is 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 hi-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.
Three alternative host interface options are available:-
- 5Volt PCI-18 interface card for Windows PC’s.
- 3.3Volt PCI-18V3 interface card for use with Mac G5 computers.
- USB-18 USB host interface and interconnecting cables.
- 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 µS steps (200 kHz max aggregate)
- Programmable input gain: 1x, 2x, 5x, 10x
- Analog input range: ±10.24 V
- Four pseudo differential analog output channels
- Four 18-bit instrumentation grade D/A converters
- Analog output range: ±10.24 V
- Sixteen synchronous digital input channels
- Thirty-two synchronous digital output channels, fourteen with current sink
- Sixteen asynchronous digital output channels
- Large 1024 kilosample FIFO
- PCI, and USB 2.0 host interfaces available
- Easy installation, no IRQ or DMA channel settings
- Compatible with Windows XP, Windows 7 (32/64-bit), Windows 7 (32/64-bit), MacOS X 10.4 (or more recent), LabView for Windows, MatLab and Linux
Supplied
- Mains Lead
- Users Manual
Recommended Host Interfaces:
One of the host interfaces below is required to operate the ITC-18.
- PCI-18: The PCI-18 host interface card is a short form factor, 32-bit, 33 MHz 5 V PCI bus plug in card. The PCI-18 is compatible with Apple, PC, and other computer systems that feature a 5 V PCI Bus. Please note that the PCI-18 can only be physically connected to a 5 V or Universal PCI bus connector.
- PCI-18V3: The PCI-18V3 host interface card is a short form factor, 32-bit, 33 MHz 3.3 V PCI bus plug in card. The PCI-18V3 is compatible with Apple G5, PC, and other computer systems that feature a 3.3 V PCI Bus. Please note that the PCI-18V3 can only be physically connected to a 3.3 V or Universal PCI bus connector.
- USB-18: The USB-18 host interface is a USB v2.0 high-speed (480 Mbps) interface for Apple, PC, and other computer systems that feature USB v2.0 high-speed ports. An extra feature of the USB-18 is the addition of sixteen asynchronous digital input and output lines.
