PRECISION 28000
Signal Conditioning
System

28316B 16-Channel Long Distance TEDS/IEPE Accelerometer Conditioner

General Purpose Vibration Measurements

The 28316B offers a mixed mode interface supporting IEPE and TEDS sensors.

The 28316B 16-Channel Long Distance TEDS/IEPE Accelerometer Conditioner provides signal conditioning for either TEDS equipped or traditional IEPE sensors. Ideal for modal and structural analysis applications, the 28316B card is equipped with Precision Filters’ long-distance TEDS (LDTEDS) technology that extends communication with TEDS equipped sensors to 1500 feet. The card supports programmable filtering, gain and IEPE current. In addition, sensor open, short and bias level are monitored and reported.

The 28316B provides a mixed mode transducer interface in conformance with IEEE 1451.4 Smart Transducer Interface.

The mixed mode interface supports IEPE (Integrated Electronic Piezo-Electric) 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.

For IEPE sensors or remote charge preamps, a programmable current source with 26 V compliance is provided.

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.

The 28316B is equipped with Precision Filters' proprietary Long Distance TEDS (LDTEDS) hardware. LDTEDS can communicate with sensors at distances out to 1500 feet. 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.

The 28316B provides a selection of 4-pole filter characteristics with
–5% corner frequencies. Filter bypass allows amplified wide-band representation of input signals. Test inputs (voltage and current), along with output monitor, make the system ready to work with the 28000 test subsystem hardware to support Go/No-Go tests and Factory Acceptance tests. The Output Bank Switch option allows the 28316B to work with data acquisition systems with a smaller number of channels.

28316B Features

16 channels per card; 256 channels per chassis
Precision Filters LDTEDS (Long-Distance Transducer Electronic Datasheet) compliant
Gain x0.5 to x128 with 0.05% resolution
Auto-ranging gain for best ADC dynamic range
Programmable 4-pole filters: BE4, BU4, EL4 and TD4
Programmable corner frequency settings
Current settings of 0, 1, 2, 4 or 8 mA (programmable, selected per card)
Sensor fault detector, open and short
Sensor bias detector, in-range or out-of-range
AC test current checks sensor, cable and signal conditioner health
Overload detection
Output monitor, selects any one of 256 outputs
Test input for each channel
Bank switch options switches the 256 output in banks of 16, 32, 64 or 128 channels to mate with various size data acquisition systems

Bank Switch

The Output Bank Switch option allows the 28316B to work with data acquisition systems with a smaller number of channels. Ideally, the 256-channel signal conditioning system would be mated with a 256-channel data acquisition system. However, the user may have a smaller DAS with 16, 32, 64 or 128 channels. The Bank Switch, Option B, provides a means of mating to a lower channel DAS:

16 banks of 16 channels for a 16-channel DAS
8 banks of 32 channels for a 32-channel DAS
4 banks of 64 channels for a 64-channel DAS
2 banks of 128 channels for a 128-channel DAS

The bank switch can be set manually for sixteen, eight, four or two banks. The bank switch outputs are buffered and brought out through the front panel 37-pin connector.

Sensor and Cable Health

Test inputs (voltage and current), along with output monitor and test circuits on the 28000C-BIF1-FT Backplane Interface Card, make the system ready to work with the 28000 Test System hardware to support Go/No-Go tests and Factory Acceptance tests.

Traditional Go/No-Go tests for an IEPE sensor allow insertion of a test signal to check the signal conditioning channel. It is also standard to provide open and short detection on the sensor cables.

The 28316B provides two additional tests to verify sensor health. The operating bias point of an IEPE sensor may change before failing, so measuring the bias point is a means of monitoring the sensor health. The 28316B provides a bias point detector with user specified limits. The second check is a measure of the output impedance of the sensor buffer, which may shift suddenly with a damaged sensor. A small AC current is superimposed on the DC IEPE supply. The small AC voltage developed across the sensor’s output stage can be used to infer the device’s output impedance. In addition, the small output voltage can be used to provide an end-to-end check of the sensor, cable and signal conditioning system.

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Auto Gain Ranging Mode

The auto gain ranging mode provides a means of setting up all 256 channels in three gain ranging periods, where the gain ranging period, T, is selected from 1/8 S to 128 S depending on the signal type (periodic or random) and the response of the structure (narrow-band or wide-band). When the auto-ranging is initiated, all channels are set to a gain of x8 and the output overload detector determines if the channel output exceeded the overload level at any time during the period. If the overload was exceeded the gain is set to x2 and if not the gain is set to x32. The overload detectors are reset and the overload detectors operate for another period (2nd period). At the end of three periods (3T) all 256 channels have been set to the operating gain. The output overload detector is set to allow for crest factor and creep.

TEDS Support

TEDS (Transducer Electronic Data Sheet) reader/writer option is available as Option T on the 28316B card. Option T provides the ability to read stored data on TEDS-compliant devices. Precision Filters' proprietary Long Distance TEDS (LDTEDS) support provides the capability to communicate TEDS information across signal lines up to 1500 feet long.

The separate TEDS reader/writer program 28000-TEDS-READER is required to support Option T. The reader/writer program is compatible with IEEE 1451.4 V0.9 transducers.

TEDS data is displayed as a spreadsheet that can be displayed and saved as a configuration file. 28316B system information such as channel number and a time stamp of the time that TEDS information for each channel was last read are provided.

Manufacturer’s information read from the sensor including manufacturer name, model number, version number and version letter of the sensor together with sensor serial number and cal date are displayed in the table. Accelerometer Template Information in accordance with the IEEE standard is displayed as well as application dependent information. Sensor Sensitivity is used to set channel gains for EU scaling of 28316B outputs.