Best DAQ Approach For Machine Controls?

Programmable Automation Controller (PAC) and Data Acquistion (DAQ) Systems Each Offer Unique Avantages in Terms of Information Access and in Granularity

By Control Design Staff

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As our machine controls grow more sophisticated and powerful, we think that we can and should provide additional data acquisition and monitoring capabilities beyond routine speed and rotational condition monitoring. We want to help willing customers obtain useful, real-time operating data, but we also want to capture some key operating variables that will help us design better-performing and more reliable machines. We've used standalone DAQ systems, and now are considering whether the data acquisition capabilities of PACs and newer PLCs might be a better path. We'd like to hear from others who have experience with both.

—From April '14 Control Design


You Can Leverage Both

Effective rotating equipment condition monitoring necessitates the intelligent amalgamation of machine and process variables with the capture of high-speed, qualitative analog sources. Typically, this process is undertaken by complex and costly condition monitoring systems that create additional barriers to value by removing the reliability analysis from those closest to the equipment.

Programmable automation controller (PAC) and data acquistion (DAQ) systems each offer unique advantages in terms of information access and in granularity. The greatest benefit is realized from those systems that leverage both to deliver accessible, yet comprehensive insight into the condition of the machinery. PACs provide a foundation to facilitate the collection of existing process machinery operating parameters and protection events. This information is leveraged most effectively, not in isolation, but when used to provide event-context interpretation supporting the understanding of more granular data available from high-speed DAQs.

Our company has successfully embodied its valued OEM machinery knowledge within our Envision condition monitoring system worldwide. The Envision suite unifies the advantages of both PACs and DAQs into an understandable, common user interface that provides accurate, timely diagnostic information to both operators and rotating equipment engineers alike.

Neil Anderson,
Global Integration Manager,

Use a Unified System

Today, machine builders who seek to implement more advanced condition monitoring systems no longer have to rely on standalone, black-box systems. PC control, for example, represents one unified system to interface, collect, analyze, store and display the data for any monitoring and measurement application, from simple to advanced. Another advantage of PC-based control is that when today's modern multicore processors are paired with our standard TwinCAT software, it's rather easy to bundle this functionality with the meat and potatoes machine functionality, such as PLC, motion control, HMI and even things like robotics, all on one hardware device. Even better, users can intelligently separate the tasks to individual cores. The benefit here is that very specialized tasks such as condition monitoring can run without sacrificing the performance needed for the connected I/O hardware, the HMI driven by this same computer or any other inherent machine control functionality, all performed by one industrial PC (IPC).

Once the measured data has been collected and pre-conditioned, it can be handed off to a standard condition monitoring software library such as in our TwinCAT. This solution can expertly manage the frequency analysis, statistics and classification of the signal to be monitored. In the past, as I'm sure the reader is aware, this was done by very expensive, dedicated hardware front ends. Today, we offer I/O terminals with built-in measurement and condition monitoring functionality that are directly connected to the same I/O rail with the standard I/O system. These are easily programmed and parameterized using standard software libraries that can be fine-tuned to your specific application. This is all done in TwinCAT—the same software used for all programming, including PLC, motion control, safety, etc. All the real heavy lifting of the condition monitoring and measurement is done in software running on PC-based hardware, which is flexible and can more easily accommodate changes and customizations to the system.

The standard Beckhoff condition monitoring library has frequency analysis such as power spectrum, envelope and digital filtering. Added to the mix are statistics such as moments coefficients, crest factor, etc. Homomorphic signal processing is also available such as power cepstrum, complex cepstrum, etc. Classification abilities such as pattern recognition, discrete classification (go/no go), threshold monitoring, etc., are provided. Even the motion system can play a role here, providing very fast sampled data from many types of sensors for vibration (IEPE interface accelerometer), temperature, power measurement, general mV and mA analog signals, current, velocity and position signals from our drives, just to name a few.

So what do you really need to accomplish condition monitoring and advanced measurement in a PC-based environment? You need a standard computer, ideally an IPC designed for control system applications. You also need a standard fieldbus capable of transferring large volumes of information, as well as standard I/O interface terminals to connect your scientific sensors to. Finally, you need a software platform that is capable of performing all the control functions of a PLC and has standard IT interfaces should you wish to establish remote access/connectivity.

I suggest that the reader does his/her own “condition monitoring” of the available solutions from vendors on the market. I'd strongly recommend a solution that's integrated into the standard machine control platform, which reduces reliance on dedicated, highly specialized hardware, and limits reliance on multiple software platforms that require a higher degree of specialization on the part of programming engineers.

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