Signal conditioning is the manipulation of the analog signal output of a sensor to prepare it so the data acquisition system’s digitizer can measure the signal effectively and accurately. Inadequate signal conditioning can be a significant source of vibration measurement error. In fact, signal conditioning is among the most important components of a data acquisition system because, unless real-world signals are optimized for the digitizer chosen, the accuracy of the measurement will be uncertain.
I've written this post to give you a basic overview of signal conditioning for accelerometer-based vibration measurement including:
Filters reject unwanted noise within a certain frequency range. Low-pass filters are often used to block out noise in electrical measurements. Filtering can also prevent aliasing from high-frequency signals by using an anti-aliasing filter to attenuate signals above the Nyquist frequency (the minimum rate at which a signal can be sampled without introducing errors, which is twice the highest frequency present in the signal). Anti-aliasing filters are a form of low-pass filter characterized by a flat passband and fast roll-off. Because accelerometer measurements are commonly analyzed in the frequency domain, anti-aliasing filters are ideal for vibration applications.
Amplifiers increase the signal’s voltage level to match the analog-to-digital converter (ADC) range, thereby increasing the measurement resolution and In addition, locating external signal conditioners closer to the signal source improves the measurement signal-to-noise ratio by magnifying the voltage level before it is affected by environmental noise.
Electrical isolation breaks the galvanic path between the input and output In this way, unwanted signals on the input line are prevented from passing through to the output. Isolation is required when a measurement must be made on a surface with a voltage potential far above ground. Isolation is also used to prevent ground loops. Voltage signals that fall well outside the range of the digitizer can damage the measurement system and injure the operator. For that reason, isolation is usually required in conjunction with attenuation to protect the system and the user from dangerous voltages or voltage spikes.
Many types of transducers, including accelerometers, require external voltage or current excitation. Accelerometers often have an integrated amplifier, which requires current excitation provided by the measurement device.
Linearization involves converting a non-linear input signal to a linear output signal. It is necessary when sensors produce voltage signals that aren’t linearly related to the physical measurement.
Proper selection and setup of the data acquisition system is one way to avoid any errors conditioning can artificially create. Another option, however, is to consider a vibration data logger that incorporates the data acquisition system with the accelerometer and other sensors embedded into a signal package. This has the benefit of really streamlining the set up by the end-user as well as ensuring the mating between the accelerometer and DAQ system is correct.
You can always contact us for help in determining the signal conditioning approach best suited to your vibration measurement environment. We also offer a range of vibration recorders to check out if you are interested in a streamlined setup process.
If you found this blog helpful, you might want to check out a few more articles we have on this topic:
And for a deeper dive, check out the chapter on Digital Filtering in Tom Irvine's excellent PDF handbook An Introduction to Shock and Vibration Response Spectra.