1.1.1. Hardware

APEX DS systems are high speed high, high channel count data acquisition and monitoring systems built from commercially available components. APEX, Inc. can provide pre-configured “turn key” systems or can supply only the software to be installed on the user’s hardware. Various hardware configurations are supported, including:

  • PCI or PCIe (PCI Express) systems in either rack mounted or desktop configurations.
  • PXI or PXIe systems using either embedded or external controllers.
  • Standard “PC” (laptop or desktop) systems using external acquisition modules with various interfaces such as USB, Ethernet or some form of “bus expansion” chassis (Thunderbolt, PCI, PCIe, PXI or PXIe).
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Example hardware systems supported by APEX DS

1.1.1.1. Analog Input Hardware

In analog input mode the APEX DS system implements all stages of the data acquisition from analog signal all the way to processed digital data. It is fully in control of the data acquisition hardware. This means that besides the actual data collection, all hardware configuration and control functions are also implemented by APEX DS. Different types of ADCs (Analog to Digital Converters) are supported in this mode, below is a comparison of their features:

  • Multiplexed ADCs: These are devices that have a single analog to digital converter and a switching circuitry that multiplexes the input of this converter between multiple channels. Typical features:
    • Least expensive, but also the lowest quality input option.
    • Up to 128 channels per device, 14 or 16 bit precision, up to a few million samples per second aggregate sample rate.
    • Channel count vs. bandwidth trade-offs are possible as the available bandwidth is distributed between channels.
    • Not suitable for phase measurements as each channel is sampled at a different time.
    • No anti-aliasing.
  • Simultaneous sampling ADCs: These devices have an independent analog to digital converter for each channel. Typical features:
    • Moderately expensive.
    • Up to 64 channels per device, typically 16 bit precision, up to 500kHz sample rate.
    • Highest quality data input (less noise, better linearity, etc.).
    • Suitable for phase measurements as each channel is sampled at the same time.
    • No anti-aliasing.
  • Sigma-delta ADCs: These devices have an independent high speed but low bit count (typically 12 or less) analog to digital converter for each channel. The input signal is sampled at some multiple of the final sample rate and digitally filtered to provide a more accurate (higher bit count) but lower frequency output. Features:
    • Most expensive.
    • Up to 32 channels per device, 16..24 bit precision, up to 200kHz sample rate.
    • Typically more noisy than simultaneous sampling ADCs.
    • Suitable for phase measurements as each channel is sampled at the same time.
    • Provides anti-aliasing.
    • The effect of the anti-aliasing filter is typically visible near the Nyquist rate (starting between 80..95% of Nyquist).

The input circuitry of some analog to digital converters is not suitable for interfacing them directly to common dynamic sensor types (strain gauges, accelerometers, piezo sensors, etc..). Such sensors typically require power in the form of voltage or current excitation and will provide low level outputs that need to be amplified to be compatible with the inputs of the converter.

However. many recent acquisition devices include a configurable preamplifier stage that allows directly interfacing them to various sensor types (IEPE, strain gauges, charge, etc..). Most such acquisition devices have user configurable analog input settings such as gain, excitation, bridge completion, etc.. The APEX DS software will fully support all available settings on such devices.

Note

It is highly recommended to become familiar with the particular hardware configuration before the system is used for data acquisition. The Appendix contains information on some of the more common supported ADCs and signal conditioning devices.

1.1.1.2. Digital Inputs

APEX DS can also act as a monitoring system for digital data streams. The key difference in this case is that the actual data acquisition is performed by some external system, APEX DS only has access to the already digitized data. In this case APEX DS may have incomplete control over the data acquisition process, so in some cases compromises (data loss, incomplete knowledge of the acquisition parameters, etc.) are to be expected. Typical usage scenarios for this case include:

  • Ethernet interfaced devices. In this case the manufacturer packages the ADC hardware with an embedded controller that provides some form of network interface for configuration and data streaming. Configuration may be performed by the APEX DS application or an external utility.
  • Monitoring a digital data stream provided over a network interface by some other manufacturer’s complete data acquisition system. Examples are digital telemetry systems or some digital data recorders that have real-time data streaming capability.

1.1.1.3. Extensible Device Support

APEX DS uses a modular driver architecture for supporting acquisition devices from many different manufacturers. For each supported device type (or groups of similar devices) APEX maintains a separate “plug-in” driver package that has to be added to the “standard” APEX DS installation. This way different users with different hardware configurations can customize their software installation according to their needs.

Note

Driver plug-ins for new devices can be created either by APEX (upon request) or by users themselves. For the second case the APEX DS API package contains all the necessary documentation, software interfaces and examples.