On Wed, 4 Apr 2018 12:57:03 -0700
"John Dammeyer" <jo...@autoartisans.com> wrote:

> In the past ESTOP appeared to be pretty simple a 12V or 24V control signal 
> was routed through any number of Normally Closed (NC) switches and then run 
> into relays and or opto-isolated inputs. Any ESTOP even would then interrupt 
> the control voltage and relays would open dropping all power.
> However things have changed a bit.  With PCs in the mix, rules changed and 
> PCs and control systems could stay active but anything in hardware dangerous 
> to humans was now switched off by the signal interruption.
> Enter a wide variety of motor controllers.  The HP_UHU has an active low 
> ESTOP IN/OUT signal.   A low on the ESTOP input shuts off power to the drive 
> control logic.  If the drive has  a fault, it brings this line low too and 
> any other HP_UHU drives are also then pulled into ESTOP mode.   I think this 
> would be better identified as ENABLE rather than ESTOP.
> The STMBL AC Servo drive I'm currently working with has an ENABLE high input. 
>  So when Low it's disabled and stepping pulses can't move the motor.

Then working with frequency inverters I come upon the term "safe torque off" 
and are pretty sure there are special requirements on this signal. I think this 
particularly apply to DC motors since failure mode close may cause it to run at 
full speed.

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