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LE 05 - Emergency stop button installation

WARNING

Make sure the whole control station is not energized before touching or starting your exercise!


The emergency stop button function is to cut the energy for the whole circuit so that every machine linked to it should stop.

Objective

Learn where to install the emergency stop button and its signaling pilot light, how to install it and how it works.

Material

  • Multimeter

  • AC/DC power supply. Input 120V AC and output 24V DC, 1A (at least)

  • Push button (green )

  • Push button (red)

  • Pilot light (green). 24V DC

  • Pilot light (red). 24V DC

  • Encapsulated relay 24V DC with contacts for 8A 250V

  • Emergency stop button

  • Bulb light. AC

What to do

For this exercise an emergency button is to be installed so that power can be interrupted in case of accident or malfunction. For this case, the bulb light should work as a heavy equipment.


  • Follow the same steps as for LE 04

  • Connect the emergency stop button on the (+) DC wire (before any of the rungs)

  • Set on the power supply

  • Use the following ladder diagram:


Ladder diagram for emergency stop button installation


In the above diagram ES stands for emergency stop.

Notice that the encapsulated relay must have at least 3 pairs of contacts in order to follow the above ladder diagram as is. However, if the available relay only have two pair of contacts you may use a pair for the DC connections and the other one for the AC connection and the diagram must be adapted as follows,
Ladder diagram for emergency stop button installation in the case of an encapsulated relay with only two pairs of contacts

In the above diagram the contact numbers are only for reference and may change from one supplier to another. Terminal 1 corresponds to the common wire. Also, the branch for terminal 1 at the start button is only fictitious since it was previously connected in rung 0 (do not connect that branch).


  • The whole circuit should turn off when the emergency button is depressed

  • Check for continuity if needed

How to do it

For this exercise the same setup developed for LE 04 is to be used. Details shall be omitted but refer to LE 04 for more information.


Step 1. Identification of the emergency stop button

This is also known as mushroom head button. This easily recognizable for its color and shape,

Emergency stop button


These types of buttons usually have two contacts: one NC contact to be used for the stop function and a NO intended to energize a pilot light to indicate failure.


Siemens emergency stop button contacts sketch

Step 2. Emergency stop button connection

Starting with the circuit built in LE 04, notice that a new rung had to be introduced to give space for the emergency stop button, which should be connected in rung 0. The NC (1,2) contact should be related to rung 1 so that when this button is depressed the NC contact should open and shut power to the whole circuit.


Step 3. Emergency pilot light (red) connection

As the emergency stop button is depressed a red pilot light should turn on to visually indicate that an emergency has occurred and that an action has to be taken. This pilot light is to be in series with the emergency stop button while the NO (4,3) contact is in parallel with it.

Red pilot light for emergency stop button

Step 3. Energizing the loop

In order to power the loop you should activate the circuit breaker to the ON position with the lever upl and the green indicator being shown.

Thermal circuit breaker

Step 4. Using the buttons

If your connection was right then as the loop was powered, nothing should happen and only the green pilot light should turn on, indicating that everything is OK. However, when you push the start button the bulb should turn on and keep in this state. Next, when you push the stop button the bulb should turn off.


Now, supposedly, an emergency is occurring and you need to power off of the whole system (equipment, for example). Then, what you need to do is to press the emergency stop button. The bulb should turn off and the red pilot light should turn on (to indicate that an emergency has occurred). Once you push the emergency stop button it automatically latches itself so that power to the system remains interrupted.


If you need to restore power to the system the emergency stop button needs to be unlatched first. Depressed down and swirl it to the right to release the button to its unlatched state. The system could be started again if the start button were depressed.

Step 5. Continuity and DC voltage test

Check for continuity at every contact and for 24V DC using the multimeter. Since you are using a power source for 24V DC you should get a reading not far from this value.




Any question? Write in the comments and I shall try to help.

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