STO (Safe torque off)

STO (safe torque off) is a safety function according to DIN EN 61800-5-2 and corresponds to an uncontrolled stopping according to EN 60204-1, stop category 0.

In the event of a requested STO, the motor is safely, immediately and automatically separated from the energy supply in the inverter if the IGBT control is safely interrupted and the motor is prevented from starting unexpectedly. If the STO is actuated while moving, the drive coasts to stop and generates the error message 2320.

The function is suitable for Performance Level (PL) d and category 3 according to EN 13849-1 if the signals 24B and 0B are interrupted in two channels with a switching device.

If the STO signal is looped through several drives, the STO state applies to all drives in this group. If a drive is in an error state due to a drive error (SBM = 0), it has no effect on the STO state of the other drives in this group.

 

Standards

EN 61800-5-2

Safety function

STO

Safe torque off

EN 60204-1

Stop category

0

EN ISO 13849-1

Performance Level (PL)

d

Category

3

IEC 61508

Safety integrated Level (SIL)

2

EN 61131-2

Interface STO

X1A.C and X1A.D (signal 24B / 0B)

 

Behavior of the motor holding brake at STO

Valid for all standard devices regardless of the revision level *)

Valid only for the following devices:A2553AD, A2777AD and E1241 if Rev. ≥ 4.00

For motors with a motor holding brake, the brake automatically closes with STO. The motor holding brake is not approved for personal protection from suspended loads! STO is always effective when the 24 VDC supply voltage at the connection X1A.C and X1A.D (signal 24B, 0B) is missing.

The state of STO has no effect on the motor holding brake. The motor holding brake is supplied by connection X1A.A and X1A.B (signal 24V, 0V).

*)

Except: A2553AD, A2777AD and E1241

 

Dynamization STO

Valid for all standard devices regardless of the revision level *)

Valid only for the following devices:A2553AD, A2777AD and E1241 if Rev. ≥ 4.00

Not possible.

The signal to control STO must be dynamic with a pulse duration ≤ 2 ms.

*)

Except: A2553AD, A2777AD and E1241

 

Reaction times

 

Valid for all standard devices regardless of the revision level *)

Valid only for the following devices:A2553AD, A2777AD and E1241 if Rev. ≥ 4.00

STO is triggered by hardware input

< 1 ms

< 5 ms

Software reacts on error (error reaction)

< 20 ms

< 20 ms

Diagnostic message is displayed

< 200 ms

< 200 ms

*)

Except: A2553AD, A2777AD and E1241

 

Further Information

Siehe '[X1A] Power supply'.

Siehe '[X1B] Power supply transmission'.

Siehe '[X08 / X09] 24 VDC supply voltage - Transmission'.

Siehe 'Connection examples for operation with STO'.

Siehe 'Diagnosis STO'.

For your safety

DANGER

Danger to life by jerky movement of the motor shaft!

If defects in the power output stage or the control thereof at the same time can occurs a short circuit in the circuit with the following effects:

 

  • Mains fuse is triggered if safety function STO is active.

  • Rest movement! Jerky align of the motor (180° / pole pair). A rotating field will not be reached.
    Example 10 pole motor:
    10 pole → 5 pole pair
    180° / 5 pole pair = 36° (Rest movement)

Check STO safety function!

The achievable safety categories are only valid if the customer will performs the following checks:

  • When startup, you must checked the operation of STO safety function and the signal transitions 'STO inactive' → 'STO active'

  • Annually review of the operation and signal transitions 'STO inactive' → 'STO active'

Key figures according to EN ISO 13849-1

Parameter

Value

Notice
PFH

2.0 E-08 1/h

2 % of SIL 2
PFDavg (T = 20a)

1.7 E-03

17 % of SIL 2
MTTFd

287 a

high
DCavg

66 %

low

Function test STO

Check STO safety function!

The achievable safety categories are only valid if the customer will performs the following checks:

  • When startup, you must checked the operation of STO safety function and the signal transitions 'STO inactive' → 'STO active'

  • Annually review of the operation and signal transitions 'STO inactive' → 'STO active'

Following states must be checked::