Understanding safety functions: Indicators and alarms

A man in a white hardhat and high-visibility vest stands in a large process plant control room holding a walkie-talkie and looking towards a screen with alarm annunciations displayed. The control room is mostly white, so the man's vest, the instruments and displays pop out of the image.

This is the final installment in the series on understanding safety functions. When indicators and alarms come up in conversations between machinery controls engineers, large process plant control rooms like those shown at left often come to mind. While this is certainly true, there are many instances on smaller machines and assembly lines where alarms…

Read More

โŒ ISO 13849-1:2023 โ€“ Do Not Use โŒ

This is a first On Thursday, 2023-04-27, ISO published ISO 13849-1:2023, the 4th edition of the dominant functional safety standard for machinery. Usually, I would be the first to tell you that you should buy the standard as quickly as possible and start using it immediately. Today is not a normal day. As Command Module…

Read More

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: 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.

Read More

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…

Read More