Page 22 - EngineerIT November 2021

AUTOMATION AND CONTROL

Cost saving is the core value of

condition monitoring

By Naiqian Ren, applications engineer

In this article the author provides a high-level discussion of sensor interfacing data acquisition
(DAQ) signal chain design considerations for condition monitoring systems. He examines how
certain design choices such as system architecture, sensor type and analysis methods can impact
the DAQ signal chain design and put these theories into practice by going through two DAQ
signal chain design examples in detail.

he core value of condition monitoring is long-term cost saving. The
cost saving is achieved through reduction in maintenance costs
Twith predictive maintenance and the elimination of unplanned
production downtime with preventative maintenance. The realisation of
such value relies on the condition monitoring system’s ability to accurately
detect and identify fault conditions in the early stages of development.
Unlike catastrophic failure at the very late stages of development,
which can often be bluntly obvious and easily detectable, fault detection Figure 1: DAQ centralised system architecture.
in the early stages of development may only cause a very slight deviation
to the asset’s normal operating behaviour. This deviation may also be Some of the key advantages of this architecture include:
transient in nature. The proper detection and classification of early • Low cabling cost. Low cost coaxial and twisted pair cables are often
fault signatures usually requires the use of high-performance sensors used for carrying signals between the sensor and the DAQ over a
of varying sensing modalities as part of the overall monitoring solution. long distance.
These sensors need to be properly interfaced with DAQ signal chains of • Robust interface. There are a number of standard interfacing
matching performance to fully utilise their sensing capability. The data protocols, such as IEPE and the four mA to 20 mA current loop,
can then be combined and processed using specialised algorithms to that are designed to ensure a robust sensor interface in noisy
determine the overall condition of the asset being monitored. environments.
Like all system designs, there are many choices to be made when • Flexible sensor support. The same DAQ system can be designed
it comes to designing a condition monitoring system. Each of these to support multiple sensor types based on the measurement
choices comes with various trade-offs and can drastically alter the DAQ requirements.
signal chain design. • Support for harsh operating environments. The physical separation
of the sensor and the DAQ signal chain allows certain sensors
System Level Considerations to operate in conditions that are usually not supported by the
System architecture electronic components, such as having extreme high/low operating
The first level to consider for a condition monitoring (CM) system is the temperature.
system architecture. There are several common CM system architecture • More efficient DAQ signal chain implementation. The signal chain
options based on the relative location between the sensor and the DAQ design can share more common blocks to improve efficiency and
signal chain, each with certain advantages. reduce cost.

DAQ centralised The typical data acquisition signal chain design requirements for a CM
A typical DAQ centralised system bundles multiple data acquisition system with DAQ centralised architecture are:
channels together in a centralised location, typically in the form of a
box/rack instrument. Sensors are remotely located and connect to the Performance
DAQ system using analogue cables. Most of the DAQ centralised systems are designed to support multiple
The DAQ centralised architecture is widely used by many existing sensor types. Some of them have the dual functionality of also being
measurement solutions. Most benchtop vibration monitoring instruments used as general-purpose DAQ instruments. These needs elevate the
as well as industrial analogue input modules employ this architecture. It performance requirements of the DAQ signal chain, and demand
is also very suitable for designing assets with built-in CM functionality, for metrics such as wide dynamic range, adjustable bandwidth, AC linearity
example when integrating CM capability in motors and pumps. and DC precision.

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