Charge/IEPE Amplifier for Shock and Vibration
28314 Quad Channel Wideband Charge/IEPE Conditioner provides
signal conditioning for both Charge or IEPE type sensors. The 28314 features
200kHz filtered and 500kHz wideband bandwidth for shock and vibration
applications.
In charge mode, ultra low drift and very large time constant
circuits allow for both quasi-static charge measurements and accurate dynamic
peak measurements.
In IEPE mode, the 28314 is equipped with Precision Filters’
long-distance TEDS (LDTEDS) capability and features programmable IEPE current to
25 mA.
Operating in either Charge or IEPE modes, the 28314 offer a
choice of 4 or 8-pole low-pass filters or 8-pole band-pass filters. Both
operating modes provide accurate measurements of wide band, low-level signals guaranteed by channel gains to 8192, frequency response to 204.6 kHz, low noise,
and high accuracy circuits.
TEDS read/write circuits are included to allow TEDS
functionality. Precision Filters' proprietary Long-Distance TEDS (LDTEDS) support
provides the capability to communicate TEDS information across signal lines up
to 1500 feet long.
The 28314 is a member of the Precision 28000 family of signal
conditioners providing four channels of conditioning per card and up to 64
channels per chassis.
Programming of the unit is accomplished via the Ethernet or
via the 28000 graphical user interface resident on a host computer.

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FEATURES
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4 channels per card, up to 64 channels per 28000 system chassis
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Dual mode: piezoelectric or IEPE
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Floating or grounded input
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Up to 200 kHz "filtered" bandwidth or 500 kHz "wide-band"
bandwidth
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Two charge conversion ranges for 50,000 or 500,000 pC FS inputs
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Extremely large time constant for quasi-static charge
measurements
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Programmable IEPE current to 25 mA
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TEDS compatible with proprietary Long-Distance TEDS (LDTEDS)
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Programmable amplifier: x1 to x8192 with 0.05/vernier
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4 or 8-pole low-pass or 8-pole band-pass filters with filter
bypass (wide-band)
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2° phase matching between any channels, DC to Fc
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Overload detection
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Precise automatic calibration
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Auxiliary front panel output connection to support
the use of custom output modules
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Card Mode: Charge or IEPE

The 28314 is a dual mode conditioner. The card can be set to
operate in Charge Mode or in IEPE Mode. The selection is made for all channels
on the card by setting the mode switch located on the front panel.
Charge Mode
In charge mode, the 28314 provides two charge conversion
ranges with full-scale inputs of 50,000 or 500,000 pC. Channel gains of up to
8192 provides charge sensitivity as high as 1.6 V/pC. A programmable input stage
allows operation with either grounded or isolated accelerometers. Extremely
large time constants allow measurement of quasi-static charge phenomena. Low
noise, low-distortion and high accuracy circuits guarantee accurate high
frequency measurements of even low-level signals.
Overall measurement accuracy is assured with built-in charge
gain adjustment circuits, which can be used in-situ to adjust gain under run
time conditions. Verification and documentation of actual charge gain can be
performed using built-in shunt calibration with secondary standard shunt
calibration capacitors. The calibrated value of shunt cal capacitors is stored
on card EEPROM and can be recalled by host software for exact span verification
or data post processing.
IEPE Mode
In IEPE mode, the 28314 accommodates long cable runs with
programmable IEPE current up to 25 mA. As with charge mode, accurate
measurements of wide band, low-level signals is guaranteed by channel gains to
8192, frequency response to 200 kHz, low noise, and high accuracy circuits.
Input signal visibility is a crucial aspect of IEPE sensors as
the sensors bias voltage is a useful indicator of sensor, cable and connector
health. The 28314 card IEPE input stage continually monitors the DC bias voltage
present on the channel input prior to the AC coupling stage. Not only is this
voltage level displayed for each channel but it is also compared to user
programmable upper and lower threshold limits to alert the user to a sudden
shift of the bias level. A system bias level report can be requested at any
time, creating a file useful for pre-test gage health documentation.
Channel Block Diagram
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Input Stage
The 28314 input stage connects to either the charge or the
IEPE front end. The input stage has low distortion, low DC drift and ultra-low
noise.
A programmable switch at the input stage is provided to
connect the amplifier to the 28000 System test bus. The test bus is used to
inject signals for performance verification.
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Amplifier and Filter
Programmable pre- and post-filter amplifiers provide an
overall gain of 8192. Gain is distributed both before and after the filter to
provide protection from large out-of-band energy or transients that could cause
clipping before the filter, distorting the data. The Gain Wizard in the GUI
allows the user to set a gain reserve and then apportions the gain between the
input and output. This provides input gain for best noise performance yet
conforms to the limitations of the user’s worst case estimate of out-band or
transient signals. Overload detectors alert the user to over-voltage conditions.
A fully buffered output having over 20 mA of drive capability may be used to
drive long output cable runs.
The 28314 contains a 4 or 8-pole low-pass filter or an 8-pole
band-pass filter with cutoffs programmable from 1 Hz to 204.6 kHz and programmable
"flat" or "pulse" mode. The "flat" mode provides pass-band characteristics
nearly identical to a Butterworth filter while providing a much sharper
roll-off. This mode is a good choice for applications such as spectral analysis.
The "pulse" mode has time domain response similar to the Bessel filter yet
provides superior amplitude response characteristics. The "pulse" mode is ideal
for time domain applications including transient (shock) measurements and time
domain waveform analysis.
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Input/Output Connections

Input connections to the 28314 card are made at the two rear
panel connectors. Each input connector provides connections for both charge mode
and IEPE mode for two channels.
The 28314 card output connections are made at the rear panel
50-pin D-shell connectors. The 28016B-M3 mainframe provides four 50-pin
connectors, which provide four outputs per card slot in the mainframe. The
28008-M3 frame provides two 50-pin connectors.
In addition, an
auxiliary front panel output connector is provided to support the use of
custom output modules.
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The 28314 provides a mixed mode transducer interface in
conformance with IEEE 1451.4 Smart Transducer Interface. The mixed mode
interface supports IEPE (Integrated Electronic Piezoelectric) sensors powered
by current source and TEDS (Transducer Electronic Data Sheet) capable sensors.
TEDS information such as manufacturer name, serial number, calibration data,
etc. are readable by the system for use in system scaling, identification,
bookkeeping, troubleshooting and other functions.
TEDS sensors may be effectively applied to test models;
however, there is a restriction that the cable run between the signal
conditioner and the sensor be limited to 400 feet in order to be able to
properly read the TEDS. For applications such as weapons test or vibration test
on large structures, safety, environment, test article size and other factors
often require cable runs in excess of 1000 feet that have until now precluded
the use of TEDS equipped sensors.
To overcome the communications distance limitations of
conventional TEDS, the 28314 is equipped with Precision Filters’ proprietary
Long-Distance TEDS (LDTEDS) hardware. The proprietary LDTEDS circuitry uses an
analog-to-digital converter to digitize the TEDS waveforms and utilizes a
digital signal processor to process the TEDS data. LDTEDS can communicate with
sensors at distances out to 1500 feet.
To learn more about LDTEDS read the white paper "LDTEDS:
A Method for Long Distance Communication to Smart Transducers with TEDS".
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Download the
Spec Sheet
from the Reference Library
Request
Product Information
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Applications Examples
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Load, torque, dynamic force, dynamic pressure,
shock, vibration and acoustic measurements
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Piezoelectric crash tests
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Ballistics shock testing
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Machine health monitoring
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Structural response tests
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Flight tests
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Wind tunnels
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Ultrasonic transducers
Reference
The following Specifications
are available in Precision Filters'
On-line Library
for downloading:
28104A Quad Bridge Conditioner Specifications
28208 Octal Thermocouple Conditioner
28302B Dual
Vibration Amplifier
27304 Quad Dual Mode Charge Amplifier
28314 Quad Dynamic Charge/IEPE Conditioner
with LDTEDS
28316B 16-Channel TEDS/IEPE Accelerometer
Conditioner
28454A Quad Conditioner Specifications
28524 Quad Frequency to Voltage Converter
Modules
28608B Octal Programmable Filter Amplifier
27708A Octal
AC/DC Amplifier
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