7216 Description
Pacific’s Model 7216 aka “DAS Brick” brings a brand new look
to strain gage and transducer data acquisition. A network
appliance, it conditions, amplifies and digitizes the outputs of up
to sixteen strain gage, bridge or voltage transducers. The rugged
enclosure is designed for installation in wind tunnels, engine test
stands and other facilities where it is desired to locate the DAS
close to the test article reducing installation and cable cost and
improving signal quality and reliability.
Fully self-contained, the 7216 provides transducer excitation,
bridge completion and balance. The transducer output is
amplified, filtered to remove signal components that could
produce alias errors and digitized to 24-bit resolution. The
digitized transducer output is digitally processed providing
multiple sample rates, an 80 dB/octave FIR filter and 32-bit
floating point output format in millivolts referred to input,
millivolts referred to output or user defined engineering units.
Programmable signal conditioning includes voltage excitation,
bridge completion for 120 and 350 Ohm strain gages, shunt
calibration and automatic balance. Conditioned and amplified
transducer signals are digitized, processed and output at 10 to
24,000 samples per second as selected for individual channels.
A digital signal processor (DSP) provides low-pass filtering
selectable from 10 Hz to 3,000 Hz with 80 db/octave roll-off.
The DSP can be custom programmed to provide alternate filter
responses and perform application specific signal processing.
Each Brick has a 100BaseT Ethernet interface for control and
data output, which simplify system wiring and provides remote
and distributed operation. IRIG time may be employed to
synchronize sampling on multiple Bricks within 10 microseconds
or a timing pulse may be used to achieve better than 1
microsecond time alignment. Multiple Bricks with up to 4,096
channels may be connected on a single Ethernet LAN.
The case features interchangeable end plates that provide fully
sealed, ambient air or forced air cooling. Forced air cooling
provides the capability to operate over a wide temperature range
according to application requirements. Occupying less than 500
cubic inches and weighing less than 14 pounds the Bricks can
be installed in locations previously not suitable for data
acquisition systems. The Ethernet interface and IRIG timing
make it easy to distribute Bricks throughout the test facility
minimizing sensor cabling and installation costs.
The Model 7216 does not sacrifice performance. In fact it
features higher accuracy than most systems designed for a
laboratory environment. That’s because it is self calibrating,
taking into account temperature and excitation variations.
Accuracy is better than 0.025% for gains up to 200 and 0.05%
for gains above 200 over the temperature range -20°C to +50°C,
which can be extended to higher temperatures by forced air
cooling.
The 7216 is supported by Pacific’s PI660 software that provides
a ready-to-run application and API for user program development.
Calibration and performance verification is accomplished by
PANEL72 Maintenance and Calibration software. The ACS2000
Automatic Calibration System automates performance verification
and periodic instrument calibration.
7216 Installation
Locating data acquisition hardware near transducers at many test facilities has required
specially constructed and environmentally conditioned
enclosures. Using the 7216, the data acquisition can be
installed in unprepared locations and the only external
connections are power, timing and Ethernet.
7216 Details
7216 Accuracy
The 7216 maintains ±0.025% uncertainty (±0.05% for gains
above 200) over the full temperature range by continuously
correcting for temperature induced excitation, gain and zero
variations. It is initially calibrated and correction vectors are
stored in non-volatile memory. An internal sensor determines the
correction vectors applied to the data according to the device
temperature. Software is available for automatic recalibration.
Voltage calibration, using an internal, NIST traceable precision
voltage reference is provided to confirm accuracy.
7216 Signal Conditioning
The excitation output is programmable from 0 to 15 Volts with
better than 1 millivolt resolution. Calibrated 1 Volt ±0.1% steps
are also provided. Output current is 50 mA. The excitation
voltage is continuously monitored by sense inputs connected to
the sensor and adjusted as necessary to maintain a constant
voltage over the full temperature range. Bridge completion is
programmable for quarter-bridge, 120 and 350 Ohm gages, half
and full bridges. Other values can be supplied on request. Two
steps of shunt calibration are provided. Transducer balance
employs a high-resolution DAC and is initiated by program
instruction.
7216 Instrumentation Amplifier
The sensor inputs are protected up to ±50 Volts differential and
±30 Volts common mode. They are applied to a highimpedance,
programmable gain, differential instrumentation
amplifier. The amplifier has programmable gains from 1 to 1,000
providing full-scale input ranges of ±10 mV to ±10 Volts.
Calibrated gain steps with ±0.02% accuracy are provided or the
amplifier gain may be continuously programmed. Autozero
maintains the amplifier output offset within ±1 mV.
7216 Analog to Digital
Conditioned and amplified transducer signals are digitized by a
24-bit resolution Sigma-Delta analog-to-digital converter that
over-samples the analog signal enabling the use of a singlefrequency
anti-aliasing filter.
7216 Sampling
Sampling is synchronized between channels and systems
providing time aligned data. All channels are simultaneously
sampled at the highest sample rate, 24 kS/s. The sample clock
may be synchronized to IRIG A, B or G time. IRIG G time is
generate by the unit connected to the external IRIG source or
designated as the master time source if external IRIG is not used.
Distributed to multiple system it maintains channel to channel
time skew less than 1 microsecond for channels in the same or
other systems using the same master time source. If the timing
signal is not present or lost during acquisition sampling will
continue at the last programmed rate using an internal clock.
7216 Filter
Finite Impulse Response (FIR) filtering is provided. Eighty sets
of 128 FIR filter coefficients are available in each 7216
providing an extensive selection of filter frequencies and
characteristics. The coefficients are user programmable, and
each coefficient is 18 bits in length. The filters are loaded with
customer-specified default coefficients providing logical filter
cutoff selections and characteristics. The default filter
frequencies and characteristics are easily changed using program
instructions to satisfy future requirements.
7216 Data
Data are output in a digital format on the Ethernet interface. The
output data is 32-bit floating point format and can be chosen
via programming to be Volts, millivolts, microvolts, or user defined
engineering units derived from a polynomial expression. Each
system can output data from all channels at the maximum
sample rate. Data rates in excess of 7 million samples per
second are achievable from combined systems on a single LAN.
7216 Programming
All operating parameters can be set and queried using the
extensive, built-in command set. Setup information is saved in
password protected EEPROM memory on board, and it is
automatically restored when power is applied or the system reset.
The command set is well documented, and source code
programming examples are provided.
7216 Software
PI660 is the choice for test management, data acquisition, and
data display. Ready to run out of the box it is a 32-bit
application that runs on Microsoft Windows operating system. It
provides all the tools for test definition, setup & tracking,
transducer calibration, data acquisition, display, replay and
export, and test quality validation. PI660 comes with an
Application Programmer’s Interface that greatly reduces the
development time for custom operating software. PANEL72 is
Pacific’s maintenance and calibration software. It may be used
to troubleshoot installation problems and calibrate the 7216.
7216 Connections
Initializing communication with the
7216 is simple. Commands are
included that enumerate the 7216
devices on the network. After the
enumeration operating software
creates a socket interface between
itself and each 7216. Simple Send
and Receive network commands are
used to communicate. Status LEDs
that assist with initial setup are
located on the connector end of the
enclosure. Multiple systems, up to
4,096 channels, may be connected
to a single Ethernet LAN.
16-Channels strain gage, bridge or voltage
