Emergency Off (EMO) vs Emergency Stop

EMO Button, red with yellow surround. Credit: D. Nix

The concept of Emergency Off (EMO) used by the semiconductor manufacturing sector is similar in many ways to the emergency stop used in all other types of machinery, with some differences. This article covers the differences between these concepts. NOTE: This is a long post! TL;DR: EMO and emergency stop are very similar; however, some…

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Understanding Safety Functions: the Safety-related stop function

A stop sign - A red octagon with a white border, and white block text reading STOP.

The most used safety function on machinery is the safety-related stop function. The requirements discussed in this post are not generally applicable to process-related stop functions unless the process and safety stop functions share the same control system hardware and software.

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Manual reset using an HMI

A Siemens HMI displaying control functions and data.

Update: Things have changed a bit since this post was first published in 2021. There are now some safety-rated HMIs available from big controls companies like Siemens, so if you are considering this approach, consult with your controls vendor to see if their HMIs can meet the requirements of ISO 13849-1. Ed. – 2022-05-10 Question: Can…

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More E-Stop Questions

An emergency stop button on an industrial control console is shown in the foreground, with the rest of the controls devices shown in soft focus behind it.

Here are some more questions I’ve been asked regarding emergency stop requirements. These ones came to me through the IEEE PSES EMC-PSTC Product Compliance Forum mailing list. Primary Sources There are three primary sources for the requirements for emergency stop devices: [1] Safety of machinery — Emergency stop — Principles for design, ISO 13850. International…

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Can Emergency Stop be used as an “on/off” control?

Emergency Stop Button

Every couple of months I get an email asking me if there is any reason why e-stop functions can’t be used as the primary power control (on/off button) for machinery. Following a recent exchange, I thought I would share the reasons for why this is such a bad idea. The short answer The short answer…

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