Vibration and Acceleration Signal Conditioners Information

 

Vibration and acceleration signal condtioners from Columbia Research Labs, Inc.Vibration and acceleration signal conditioners manipulate analog signals to prepare them for further processing using analog-to-digital conversion. This technology facilitates systems relying on vibration or acceleration measurements obtained from sensors. Conditioning tools perform specific activities, including filtering, amplifying, converting, matching ranges, isolation, and other activities for producing suitable data for digitization.

 

Conditioning instruments receive input, including AC voltage, DC current and voltage, electric charge and frequency.  

 

Some signals are received at a very low output and need amplification to enable digitization. Other instruments involve excitation for proper operation. The control engineering disciplines combine sensing functions with conditioning to deliver actionable data to control mechanisms.

 

Vibration and acceleration signal conditioners come in a myriad of types. Simpler models offer limited monitoring and conditioning options while advanced versions provide a broader scope of such functions. Interface options include accelerometers and tachometers.

 

How Vibration and Acceleration Signal Conditioners Work

 

 

 

What Is Signal Conditioning? Part 1: An Overview

 

Video Credit: Dataforth

 

Conditioning units designed for digitizing vibration or acceleration information rely on an array of variables. Integrated or connected data acquisition instruments such as tachometers, accelerometers, and other tools provide the inputs. Sensor and accelerometer measurements involve several linked processes to ensure accuracy. These include:

 

Amplification and Signal Excitation

 

Signal amplification increases signal resolution and improves the signal-to-noise ratio. Unmodified accelerometer output charge yields a low voltage. As a result, it requires connection to a charge-sensitive amplifier to reduce noise and output impedance. Amplifiers are powered by external current and require different amounts of excitation voltage depending on the particular accelerometer.

 

Testing conducted at very high frequencies (above 100 kHz) requires sensing components capable of handling such situations. Voltage amplified platforms respond to 1 MHz frequencies while standard charge amplifiers respond to 100 kHz. This is caused by amplifier limitations and the effect of capacitive filtering. Amplifier types include peak detectors, sample and hold, log, antilog, instrumentation and programmable gain amplifiers.

 

 

AC and DC Coupling

 

Signals sent by a sensor consist of AC and DC components, with the DC portion offsetting the AC portion starting at zero. DC offset is eliminated from the system through AC-coupling via a capacitor combined with the signal. AC-coupled mechanisms remove the long-term DC drift occurring in sensors as a result of age and temperature impact. This leads to significant improvement in the resolution and dynamic range attributed to a system.

 

DC coupling results in any DC offset passing to the ADC (analog-digital converter). It is optimal in situations where the DC content is crucial, or the signal source has minimal amounts of the offset voltage. AC-coupled mechanisms are preferred if the source has a substantial amount of undesirable offset.

 

Grounding

 

Vibration and acceleration signal conditioner from National InstrumentsVibration measurement is subject to irregularities caused by noise. Proper grounding diminishes this effect. Only one component is grounded, either the signal conditioning input or the sensor, to avoid improper grounding.

 

Long cables disrupt vibration measurement by affecting frequency response. The introduction of insufficient current to drive cable capacitance generates noise and distortion in the setup. Maximum frequency subject to transmission over a cable’s length is determined by the ratio representing cable capacitance and peak signal voltage to the available current emanating from a conditioner.

 

Filtering

 

Signal frequency spectrum holds a certain volume of invalid data. As a result, filtering is the primary conditioning task. A system’s sampling rate should equal no less than twice the frequency of any acquired signal to carry out precise calculations. The addition of a low-pass filter ahead of the sampler and the ADC ensures proper frequency ranges are sampled. The filter attenuates high-frequency noise and eliminates any distortions in measurements in case of aliasing components registering higher than the sampling rate.

 

The conditioning units monitor vibration using four primary detection types:

 

  • Root-mean-square (RMS) and peak -- Useful for monitoring of general machine conditions by analyzing overall vibration.
  • True peak -- Ideal for measuring vibrations of a short duration, when capturing simultaneous events is essential.
  • True peak-to-peak -- Suitable for analyzing displacements by capturing and holding maximum total vibration data.

 

Dynamic Range

 

Dynamic range consists of a maximum and minimum signals estimated simultaneously. An input range and maximum dynamic range determine the input parameters attributable to the mechanism.

 

Tachometers

 

Tachometers are used in combination with vibration and acceleration signal conditioners to capture the rotational speed of the equipment. They also provide phase information, making them valuable in sound and vibration applications. Tachometers enable users to align frequency components with shaft speed and position.

 

Features

 

Vibration and acceleration signal conditioning instruments support a comprehensive set of features, including the following:

 

Sampling frequency -- Represents the frequency at which the analog signal sampling occurs.

 

Resolution -- Indicates the level of fineness of digital output representing analog values.

 

Accuracy -- Refers to the results of signal conditioning linearity, hysteresis, considerations of temperature, etc.

 

Analog input channel -- Specifies the maximum possible analog channel inputs.

 

Output -- Includes frequency, voltage outputs and voltage current levels. Frequency or a pulse signal is reported as amplitude modulation (AM), frequency modulation (FM), or pulse width modulation (PWM).

 

Form factors:

 

  • Printed circuit board (PCB)
  • Panel Chassis Mount
  • Modular Bay/Slot System
  • Rack Mount
  • DIN Rail (DIN stands for Deutsches Institut fur Normung, a German standardization organization)
  • Stand Alone 

Other features include:

 

  • ESD protection
  • Front Panel BNC for dynamic signal output
  • Accelerometer input
  • Tachometer interface
  • Buffered vibration output
  • Selectable filtering
  • Integration
  • Detection
  • OK Circuit LED
  • Dynamic output 

Applications

 

Vibration and acceleration signal conditioners serve a diverse scope of applications, including:

 

  • Isolation amplifiers
  • Signal isolators
  • Multiplexers
  • Bridge conditioners
  • Digital-to-analog converters
  • Frequency converters
  • Current loop converters
  • Charge converters
  • Pumps
  • Fans/Blowers
  • Motors
  • Chillers
  • Mixers
  • Gears
  • Compressors
  • Groundwater monitoring
  • Pollution measurement
  • Automotive
  • Seismic 

Selection Conditions

 

Signal conditioning equipment operates both as stand-alone units and in combination with other devices. Review manufacturer’s specifications to determine if the particular unit is compatible with the intended use. For specialized applications, consider evaluating the customization options available for the product.

 

Standards

 

IEEE Signal Processing - Digital Signal Processing Handbook

 

 

Image Credits:

Columbia Research Labs, Inc. | National Instruments |