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: 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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Understanding safety functions: Local control

Control system remote control schematic showing the local control and remote control locaitons, the machine controller and the control system I/O.

The local control function is important to understand when designing machinery control systems. If the failure of the local control function could lead to increased risk to the user, it is a safety function. This article explains the local control function from a functional safety perspective.

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Understanding Safety Functions: the start/restart function

Car engine start/stop button

After the safety-related stopping and the reset functions, the start/restart function is the next most common. Without a start/restart function, there is no way to make the machine do what it’s supposed to do. If you’re designing a machine control system, you need to understand this function.

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Q & A: Category 2 and Testing Intervals

Logical block diagram for ISO 13849-1 Category 2 architecture.

During the Free Safety Talks with Schmersal Canada and Franklin Empire, we had a “hot question” regarding Category 2 architecture and the testing interval requirement. Category 2 in [1, 6.2.5] does not mention a minimum testing rate, but [1, 4.5.4], “Simplified procedure for estimating the quantifiable aspects of PL,” adds a requirement for test rate…

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