Measurement Computing WavePort rev.3.0 - Manual (Page 31)

WavePort User’s Manual 09-29-00 Hardware and Operation Reference 4-3
Basic Operation
WavePort/PE units integrate WaveBook/516 architecture with that of one or two Dynamic Signal Modules.
The PE8 version has one dynamic module, and the PE16 has two. The architecture includes buffered input
for all channels, individual instrumentation amp/channel, per-channel programmable gain, and an
anti-aliasing filter. The operational description is presented separately for both the WAVEBOOK Module
and the Dynamic Signal Module(s).
WAVEBOOK Module Operation
WavePort’s WAVEBOOK Module includes 8 signal-input channel BNCs (CH1 through CH8). Each of
these BNCs allows for two differential signals.
• Both signals are buffered and applied to a differential amplifier.
• The output of each differential amplifier is applied to a low pass filter.
• The signals are switched (via multiplexer) to a programmable gain amplifier.
• The amplified signals are level-shifted to the specified range. Note that unipolar offset (for sampling
signals that are always positive) and bipolar offset (for signals that may be positive or negative) are
available.
• The signal is switched over to the A/D converter. The converter digitizes the signal to16 bits in 1 µs.
• The digitized value is conditioned to compensate for gain and offset errors.
• The conditioned signal is held in a FIFO data buffer until the PC reads the data. An internal processor
checks WAVEBOOK channel 1 to determine if a valid trigger event has occurred.
• The low-latency trigger is presented to a control and timing circuit for to start the acquisition after the
trigger. The TTL trigger is taken directly from the digital I/O port.
• At every sample time, WavePort’s Digital Signal Processor reads from the scan sequence table and
accordingly programs the Control and Timing Circuit for the next sample. In regard to the next sample,
the Control and Timing Circuit selects the input channel, PGA gain, level-shifter offset, and the A/D
input source. It also conveys this information to dynamic signal modules (MODULE 1 and
MODULE 2) and precisely controls the A/D conversion timing.
• The Digital Signal Processor makes real-time sample corrections using calibration information that is
stored in an EEPROM.
• The digital I/O port is read and written by the processor to transfer bytes of digital data. The I/O port
may be used as a simple 8-bit input port or as a 32-address byte-wide I/O port.
• Acquisition data is sent from WAVEBOOK to the Notebook PC through a high-speed EPP
(Enhanced Parallel Port). The port makes use of a DB25 connector labeled “TO COMPUTER
PARALLEL PORT.”
MODULE 1 and MODULE 2, Dynamic Signal Module Operation
WavePort’s WAVEBOOK module is connected to two dynamic analog signal input modules, for PE16; and
one such module for PE8. The dynamic modules are referred to, simply, as MODULE 1 and MODULE 2.
Each module provides a means of interfacing with piezoelectric transducers. These transducers include, but
are not limited to, accelerometers, microphones, and force/pressure transducers.
Reference Note:
Appendix A contains information regarding the use of accelerometers.
MODULE 1 and MODULE 2 each include:
• excitation source for transducer biasing
• high-pass filter
• programmable gain amplifier (PGA)
• anti-aliasing low-pass filter
• simultaneous sample-and-hold (SSH) amplifiers
The gain, filter cut-off frequencies and current biasing levels are software programmable.