Safe Speed without encoder

robertmee

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Supposedly Siemens claims to be only drive to provide encoderless safe speed monitoring....how can they guarantee that without positive rotation detection....curious from a technical end.
 
For example, FHS_042014_eng_en-US.pdf

They do make this note at least "The use of this safety function without encoder is permitted only for induction motors or synchronous motors of the
SIEMOSYN series." In regards to the Safe Speed Monitor.
 
Dravik said:
For example, FHS_042014_eng_en-US.pdf

They do make this note at least "The use of this safety function without encoder is permitted only for induction motors or synchronous motors of the
SIEMOSYN series." In regards to the Safe Speed Monitor.
Click to expand...

Right.....so from a physics standpoint what is special about their motors that allows safe speed vector control without encoder.
 
Originally posted by Peter Nachtwey:

I don't believe Siemens is the only one doing it.
Click to expand...

I could kind of believe this one. Not from a technical standpoint but from a regulatory standpoint. You have to have the vision to see a market for this and the financial will to go through the regulatory process to get it approved.

Of all the players I'm surprised ABB hasn't been the first to do this. They have been beating the "we don't need an encoder" drum the loudest for the past 15-20 years.

Keith
 
As I understand the open loop vector system: The back EMF is filtered and used to determine rotor speed but this gets pretty tricky at low speeds and I believe that complex filter algorithms are in place along with motor modeling. To get accurate speed control at low speeds requires faith in your motor model so I can entirely understand why it might be restricted to certain motors or it might be they only tested it with those specific motors.

Nick
 
Manglemender said:
As I understand the open loop vector system: The back EMF is filtered and used to determine rotor speed but this gets pretty tricky at low speeds and I believe that complex filter algorithms are in place along with motor modeling. To get accurate speed control at low speeds requires faith in your motor model so I can entirely understand why it might be restricted to certain motors or it might be they only tested it with those specific motors.

Nick
Click to expand...

That's what I was wondering....historically low speed sensor less is not guaranteed with some instability. Given that safe speed is likely at low speeds I was wondering what siemens is doing different....if it's a specific motor model I wonder if a motor is changed in the future is there some remodeling that has to occur. From a liability seems problematic.
 
robertmee said:
Right.....so from a physics standpoint what is special about their motors that allows safe speed vector control without encoder.
Click to expand...
It's not a standard induction motor. That's a Permanent Magnet AC synchronous servo motor that has an induction winding for starting, but after that, it's like any Synch PM motor. So with a PM motor, it's easier to see the motor poles pass through the stator fields because the strength of the rotor field is predictable and as a synchronous motor there is no slip.
 
jraef said:
It's not a standard induction motor. That's a Permanent Magnet AC synchronous servo motor that has an induction winding for starting, but after that, it's like any Synch PM motor. So with a PM motor, it's easier to see the motor poles pass through the stator fields because the strength of the rotor field is predictable and as a synchronous motor there is no slip.
Click to expand...

Ah....thanks for the explanation
 
Section 5.2.3 of the manual Dravik linked to seems to indicate that encoderless SLS can be used with ANY induction motor. However, in another section of the same manual they indicate that encoderless SLS is ineffective if the drive is not enabled and providing energy to the motor.

Keith
 

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