Chapter 13 Sto Function Description; Sto Function Logic Table - Hitachi S1 Series Basic Manual

S1 series standard inverter

Chapter 13 STO function description

Reference standards: IEC 61508-1, IEC 61508-2, IEC 61508-3, IEC 61508-4, IEC 62061, ISO
13849-1, and IEC 61800-5-2
You can enable the safe torque off (STO) function to prevent unexpected startups when the main
power supply of the drive is not switched off. The STO function switches off the drive output by turning
off the drive signals to prevent unexpected startups of the motor (see the following figure). After the
STO function is enabled, you can perform some-time operations (such as non-electrical cleaning in
the lathe industry) and maintain the non-electrical components of the device without switching off the
drive.
Control
circuit

13.1 STO function logic table

The following table describes the input states and corresponding faults of the STO function.
STO input state
H1 and H2 opened
simultaneously
H1 and H2 closed
simultaneously
One of H1 and H2 opened, and
the other closed
+24V
H1
H2
COM
UDC+
PWM+
U/V/W
Drive
circuit
PWM-
UDC-
The STO function is triggered, and the drive stops running.
Fault code:
40: Safe torque off (STO)
The STOP function is not triggered, and the drive runs
properly.
The STL1, STL2, or STL3 fault occurs.
Fault code:
41: Channel H1 exception (STL1)
42: Channel H2 exception (STL2)
43: Channel H1 and H2 exceptions (STL3)
-227-
Switch, relay, etc.
Note:
The contacts of the safety switch must be opened
or closed within 250 ms; and the cable that
connects the inverter to the safety switch cannot be
longer than 25 m.
Corresponding fault