Dataforth Introduces Enhanced SCM5B48 Accelerometer Input Module

Careful attention to design and use of proprietary circuit techniques are integral to the enhanced version of the SCM5B48 isolated and field-configurable accelerometer input signal conditioning module available from Dataforth Corporation of Tucson, Arizona. The result is a highly accurate, low noise signal conditioning solution for aircraft and aerospace R&D, automotive noise reduction, and environmental/strength of materials applications.



SCM5B48 enhancements include accuracy of 0.2% across all gain and excitation settings with no need for adjustment. In addition, output noise has been reduced to a very low 200µVrms, which is essential for accurate measurements. As the circuit is constructed using precision parts, the need for recalibration over time is eliminated.

The SCM5B48 provides excitation to piezoelectric sensors with built-in microelectronic amplifiers, commonly known as ICP®*, IEPE*, or LIVM* sensors. The module provides a constant current excitation to the sensor, then isolates, filters, and amplifies the sensor output, yielding a high-level analog voltage output. The excitation current, signal gain, and filter high-pass and low-pass cutoff frequencies are field-configurable through a set of slide switches.

Specific applications for the new SCM5B48 module include:

• Aircraft and Aerospace R&D
• These applications cover a broad range of investigation including flutter testing, helicopter rotor reactions, military stress and structural tests, and rocket launch-pad dynamics.
• Automotive and Other Vehicles
• In order to reduce cabin noise, much effort has gone into understanding road and tire interactions and bump and jar reactions. Data are analyzed from accelerometers mounted on seats, shock absorbers, and other structural members, right down to the wheels.
• Environmental, Strength-of-Materials
• Life testing uses accelerometers to extrapolate the service life of many mechanical assemblies. For example, accelerometers are affixed to miniature assemblies in a copy machine and the system is exercised by varying the duty-cycles, ambient temperatures, and speeds to determine the best use limits.

More generic applications for the SCM5B48 include:

• Any process, industrial or other, that requires precise measurement of acceleration. Gain settings of 1, 10, and 100 offer a simple interface to sensors with a wide range of sensitivity.
• Situations where space is crucial as the SCM5B48 module provides signal conditioning and flexibility in the smallest package available.
• Monitoring applications where AC/DC coupling and/or rejection of low and high frequency noise is important; selectable high-pass cutoff frequencies of DC, 0.2Hz, or 10Hz and selectable low-pass cutoff frequencies of 2.5kHz, 5kHz, 10kHz, or 20kHz offer ample options to tune the filter characteristic for optimum performance.

Six poles of signal filtering in the SCM5B48 module result in greater than 100dB of normal-mode rejection for signal frequencies above the cutoff frequency. One pole of filtering is on the field side of the isolation barrier for anti-aliasing purposes; the remaining five-pole programmable filter is on the system side. High-pass filtering is achieved through a 2nd order passive filter, located on the field side.

As excitation current needs may vary from application to application, especially when long sensor lines are required, the SCM5B48 offers the option of setting the constant current source for sensor excitation to common values of 4mA or 9mA with a compliance voltage of 24VDC.

To ensure protection of expensive data acquisition equipment, the SCM5B48 module signal inputs and sensor excitation outputs are protected against accidental connection of voltages up to 240Vrms. The high performance isolation barrier breaks ground loops, allows operation at high common-mode input voltages and rejects large common-mode spikes, all of which contribute to preserving signal integrity.

Additional SCM5B48 key features include:

• ±0.2% Accuracy (Typical)
• ±0.01% Linearity
• 1500Vrms Transformer Isolation & 240Vrms Field-Side Protection
• ANSI/IEEE C37.90.1 Transient Protection
• 5V Power (30mA Typical)
• Low Output Noise
• Low Drift with Ambient Temperature
• -40°C to +85°C Operating Temperature Range
• CE Compliant
• CSA and FM Approvals Pending
• Mix and Match Module Types on Backpanel

Developed in response to customer requests for a compact, universal, low cost isolated signal conditioner interfacing to industry standard accelerometers, the SCM5B48 accelerometer input module ensures fully functional Instrument Class performance in a package that is smaller than competing modular products. Since its conception, the SCM5B48 has been designed for simple field reconfiguration any time the application requirements change. Any combination of selectable parameters is allowed. This flexibility enables a single module to be used in many scenarios while offering the traditional isolation and protection features of Dataforth's SCM5B family.

Measuring only 2.28" x 2.26" x 0.6" (58mm x 57mm x 15mm), the SCM5B signal conditioner is smaller than similar products, making it ideal for applications where space is at a premium.

Housed in a solid, potted thermoplastic plug-in-the-panel package with flammability rating of UL-94 V-0, the SCM5B family of isolated signal conditioners is specifically designed to protect user equipment, while reducing electrical noise and enabling convenient system expansion and repair. All SCM5B modules offer dimensional stability over temperature, chemical resistance, and electrical stability over time and temperature.

Operation and storage temperature for the SCM5B modules is -40 C to +85 C; relative humidity range is zero to 95% noncondensing. All models meet the requirements of EN61000-6-4 (radiated/conducted emissions) and EN61000-6-2 (ESD/RF/EFT immunity). For operation in hazardous environments, North American Class I, Division 2, and European Group II, Category 3, approvals are pending.

Design-in accessories for the SCM5B line include a selection of single-, dual-, 4-, 8-, and 16-channel backpanels that provide field screw-terminal inputs and screw terminal or ribbon cable output to a data acquisition system.

Custom signal conditioning models are available to meet unique signal conditioning needs, and the SCM5B48 is offered in a DIN mount configuration.

For additional information and pricing, call 800-444-7644 toll-free, or e-mail at sales@dataforth.com.

*ICP is a registered trademark of PCB Group Inc.
*IEPE is Integrated Electronic Piezo-Electric
*LIVM is Low Impedance Voltage Mode

Originally released April 2006, updated May 2007 and August 2009