Emergency Stop 1

[UKEng]

Hi,

Could I ask everyone what their interpretation is of an emergency stop in a motor control circuit. What makes it any emergency stop as apposed to a 'normal' stop function. I have seen stop buttons labelled up as emergency stop but all it does is drop the contactor out as does the normal stop button.

regards

Chunky

 

[busbar]

For a single motor or small group of motors working in a common process, there may be no formal differentiation. For more complex processes, emergency stop may imply an immediate, not necessarily immediately economic, non-orderly shutdown of a larger group of motors and related control components.

Most stop buttons are typically momentary/spring-return, whereas there seems to be a tendency for emergency-stop or master-stop controls to be maintained/locking.

 

[dpc]

Here's a couple of other issues related to emergency stop vs normal stop -

Emergency stop pushbuttons are often located near the danger points of the equipment - and separate from the normal start/stop control. In the case of a belt conveyor, you will have an emergency pull cord system running the length of the conveyor.

The second issue is that "normal stop" functions can often take time. For large pipeline pumps, it is common to close the discharge valve prior to stopping the pump. Also, motors on adjustable frequency drives are often ramped to low speed prior to stopping. So initiating a normal stop may involve waiting a while for the motor to actually stop. For an emergency stop, the motor is generally always de-energized right away.

 

[jbartos]

Suggestion: Consult:
1. NFPA for emergency stop or E-Stop requirements

http://www.nfpa.org

2. IEC standards for E-Stop

http://www.iec.ch

The emergency stops are mandatory at most machines and production lines. They are essentially for the personnel safety; however, the machinery or process safety is also added so that the personnel safety and machinery/process safety are integrated and often properly coexist.

 

[Nandkumar]

The purpose of Emergency stop is to provide immediete stopping of the equipment. This should be operated only in cases of emergencies. The Emergency Stop pushbutton wiring bypasses all normal interlocks in the circuit which in the normal process would be required to be adhered to. This speeds up considerably the stoppage time.
In NORMAL stop , the wiring is through the interlocks which ensure sequential stoppage as per the control circuit requirements.

 

[PaperWeight]

The Emergency Stop should also be a hard wired stop. Pushing the E-stop should deenergize a coil in the motor starter or switchgear and open the breaker as opposed to a soft stop, which would be an input to a PLC or other controller which would trigger a software output to stop the motor.

As was mentioned already, the E-Stop doesn't stop the motor differently really, but stops it more immediately rather than waiting for certain processes to be completed which are primarily for machine or process safety. For instance the E-stop may open the breaker before unloading the motor.

 

[servoman]

Emergency Stop:

Emergency stop should be an immediate release of all power to attached equipment. Usually a main contactor will drop out ...killing all power to all motor equipment so there will be no live parts. Initiating an Emergency Stop command must also create a situation where there must be a system reset performed before power can be restored.

IE if you pull the estop button out again power remains off until it is reset by system reset.

Eg: My motor controller is running the attached motor at full speed. E stop would kill power to the control unit and all power in the panel. IF the motor has brakes ...they would slam on and stop the system very quickly. NO brakes??? then the motor would either coast to a stop or dynamic brake (depending on the motor).


Stop...Ramp stop:

Is used to activate a controlled motor ramp to zero speed and then stand by...or after stopping release contactor to motor. This is used when all is OK but an operator just wants to halt a process. Power is still at the motor control and the motor can be easily restarted (without reset!)

For example: In a steel winder several tonnes are behind a roll of steel being wound up. Stop is pushed.....Motor control unit senses stop mode and ramps down motor under predetermined ramp untill motor has reach zero speed (power is still active). Motor stops....motor control unit goes to stand by waiting for start command. Power still active in panel.

Actually for a steel roll there are two ramp stops....one fast stop and one regular stop. Fast ramp initiates a controlled full regenerative assisted motor stop....usually at 150% - 175% of the motor name plate current to ramp to stop. The motor contoller must remain powered up during this fast ramp....once the motor is stopped the power can be dropped as in an estop situation.

 

[jbartos]

Suggestion: Visit

http://www.festo-usa.com/tips/case1.html

http://www.robotics.com/arobot/estop.html

http://www.fujitecamerica.com/escal...cial_escalators_customer_specifications.htm#4

http://www.as-interface.com/asi/safetyenglish.ppt

etc. for more info

 

[abeltio]

Chunky,
Most of the answers above do explain the difference between an E-Stop and a Normal Stop.
Let me add that the ANSI code for the e-stop is : 5, whereas for the normal stop/shutdown 94 is used.
Also:
The normal stop is usually set as a normally open contact (push to close) and may be incorporated as a software pushbutton on an OPerator Interface.
While the e-stop is usually NORMALLY CLOSED contact "hard wired" into the master protective circuit in series with other "emergency trips":
e.g.
5E 39V 12T
----]/[-------------]/[-------------]/[-----------(R)
Manual High Vibr Overspeed Trip
Emergency PB Trip Trip Coil

Hope this helps.
a.

 

[jbartos]

Suggestion to abeltio (Mechanical) Jul 29, 2002
Chunky,
Most of the answers above do explain the difference between an E-Stop and a Normal Stop.
Let me add that the ANSI code for the e-stop is : 5,
///It could potentially be except in cases where it provides "lockout". Then the ANSI device function is more appropriate.
IEEE Std 141-1993 defines Device 5 Stopping Device as a control device used primarily to shut down an equipment and hold it out of operation. (This device may be manually or electrically actuated, but it excludes the function of electrical lockout (see device function 86) on abnormal conditions. Therefore, the e-stop that locks out circuits is supposed to be marked by ANSI device 86 instead of 5.\\
whereas for the normal stop/shutdown 94 is used.
///ANSI device number 5 could potentially be used too, if the lockout function is inapplicable.\\Also:
The normal stop is usually set as a normally open contact
///Normal stops are usually normally closed push buttons that are opening circuit, which in turn trips the relays and opens the start button sealing contact belonging to the tripped relay(s).\\ (push to close)
and may be incorporated as a software pushbutton on an OPerator Interface.