MEDICAL
equipment is monitored remotely and subtle changes in behavior that may indicate a before an on-site operator has a chance to see them. In such a scenario engineers can be dispatched with advanced knowledge of what they are looking for ahead of any system failure, reducing the potential for downtime.
This is the world of preventative maintenance and monitoring. Sudden failures rarely happen without warning if you know where to look or listen. For example, a worn bearing in a fan or other
mechanism will produce more audible noise and may increase the resistance to rotating. A failing capacitor may lead to more ripple and noise on the supply line. A good failure modes and effects analysis (FMEA) can provide service engineers with a roadmap to understand and diagnose changes in equipment behavior. before they happen, large medical capital equipment increasingly includes an eye’ on areas of the design that may be subject to wear or premature failure. This can include devices such as temperature sensors to monitor additional heat generated from friction or strategically placed microphones that listen for changes in sound from a mechanism that is wearing. Monitoring becomes even more powerful and valuable if it can be done remotely, either at the customer site or, ideally, in the equipment supplier’s service department, exceeded.
Unfortunately, every additional sensor adds cost and complexity, for the sensor itself as well as the signal processing circuitry. Even if the cost is not prohibitive, in densely packed machines the required space may simply not be available.
However, there is an alternative way of checking on system health. In many cases, especially in electro-mechanical systems,
impending failure often results in changes in the power being drawn from the power source, for example, more current being drawn to drive a degrading motor to overcome increasing friction. As a result, by monitoring the output rails of the power system within large capital equipment it can be possible to provide extensive coverage of many areas subject to early wear-out and to gain insight into potential failure conditions.
Using PMBus to Implement a Comprehensive Monitoring System
With almost all power solutions being sourced as complete sub-assemblies from specialist manufacturers, the ability to monitor must be designed into the power supply from the start. Fortunately, many high-quality power solutions now include technology that allows the power supply to The Power Management Bus (PMBus) is advances in power supply intelligence. This standard, developed by several leading power supply manufacturers including founding member Artesyn Technologies
(now part of Advanced Energy), allows communication with a power supply over a digital communication bus.
C exist, there are shortcomings and, although PMBus is electrically compatible with I2
C.
PMBus is an open standard, owned by the System Management Interface Forum (SM-IF). It is royalty-free with released requirements including transport and command language. While other standards such as I2
C, it offers more features
and overcomes the noise-related and other issues often associated with I2
The PMBus command language is both extensive and comprehensive. Every value that can be written can also be read, making for a comprehensive monitoring capability for power. Examples of parameters that can be read include output voltage and power, duty cycle, switching frequency and current sensing / scaling and calibration. Typically, the host device will constantly poll all PMBus devices. Although, in the event of a fault, an individual PMBus device can alert the host immediately via an interrupt.
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