Understanding safety functions: Fluctuations, loss and restoration of power sources

Voltage vs time plot showing a voltage sag condition.

Control systems must be protected against fluctuations and power loss, whether electrical or fluidic. Fluctuations and losses are well defined in IEC, IEEE and ISO standards. Careful design of electrical systems, including the use of UPSs for electrical control systems and the careful design of pneumatic supply systems, including the proper sizing of pneumatic accumulators for compressed air-powered logic, is essential.

Understanding safety functions: Pressure or temperature

A series of pressure gauges monitoring a process.

Pressure and temperature are important safety-related parameters. The two parameters are closely linked in systems where gases or vapours are present, with behaviour governed by the combined gas laws. The temperature is also critical in mechanical systems that can overheat, like motors or bearings. Monitoring temperature or pressure requires the correct selection of instruments.

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Understanding safety functions: Safe speed and safe standstill

A red sign with white block letters reading "reduce speed."

In this post, I’ll discuss two safety-related parameters: safe speed and safe standstill. Speed control is a very common machine function. Conveyors, mixers, pumps, and many other applications rely on variable-speed drives. Some speed parameters are also safety-related because variations in speed can increase the risk to workers. See this post for more information on…

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Understanding safety functions: Response time

A stopwatche with a movong hand and athe words "response time" next to it.

This post deepens the discussion of safety-related parameters. Safety functions are control functions whose failure causes an immediate increase in risk. ISO 13849-1 [1] defines several common safety functions to develop safety-related control systems. In this post, I will discuss the response time safety-related parameter.

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Understanding safety functions: Safety-related parameters

An old, white, control panel with the paint peeling off it in many places, and many dials and gauges showing various readings.

Safety-related parameters are control system variables whose incorrect setting immediately increases the risk to the user. Some of the most common include safe-reduced speed and safe standstill, but temperature, pressure and other process parameters can also be safety-related. Defining what machine parameters are safety-related and then designing control hardware and software to meet the functional…

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