Requirements for Using the Safety-Related Function STO

General

The safety-related function STO (Safe Torque Off) does not remove power from the DC bus. The safety-related function STO only removes power to the motor. The DC bus voltage and the mains voltage to the drive are still present.

DANGER
	ELECTRIC SHOCK Do not use the safety-related function STO for any other purposes than its intended function. Use an appropriate switch, that is not part of the circuit of the safety-related function STO, to disconnect the drive from the mains power. Failure to follow these instructions will result in death or serious injury.

After the safety-related function STO is triggered, the motor can no longer generate torque and coasts down without braking.

WARNING
	UNINTENDED EQUIPMENT OPERATION Install a dedicated, external safety-related brake if coasting does not meet the deceleration requirements of your application. Failure to follow these instructions can result in death, serious injury, or equipment damage.

Logic Type

The inputs for the safety-related function STO (inputs STO_A and STO_B) can only be wired for sinking inputs.

Holding Brake and Safety-Related Function STO

When the safety-related function STO is triggered, the power stage is immediately disabled. Applying the holding brake requires a certain amount of time. In the case of vertical axes or external forces acting on the load, you may have to take additional measures to bring the load to a standstill and to keep it at a standstill when the safety-related function STO is used, for example, by using a service brake.

WARNING
	FALLING LOAD Ensure that all loads come to a secure standstill when the safety-related function STO is used. Failure to follow these instructions can result in death, serious injury, or equipment damage.

If the suspension of hanging / pulling loads is a safety objective for the machine, then you can only achieve this objective by using an appropriate external brake as a safety-related measure.

WARNING
	UNINTENDED AXIS MOVEMENT Do not use the internal holding brake as a safety-related measure. Only use certified external brakes as safety-related measures. Failure to follow these instructions can result in death, serious injury, or equipment damage.

NOTE: The drive does not provide its own safety-related output to connect an external brake to use as a safety-related measure.

Unintended Restart

WARNING
	UNINTENDED EQUIPMENT OPERATION Verify that your risk assessment covers all potential effects of automatic or unintended enabling of the power stage, for example, after power outage. Implement all measures such as control functions, guards, or other safety-related functions, required to reliably protect against all hazards that may result from automatic or unintended enabling of the power stage. Verify that a master controller cannot enable the power stage in an unintended way. Failure to follow these instructions can result in death, serious injury, or equipment damage.

WARNING

UNINTENDED EQUIPMENT OPERATION

Verify that your risk assessment covers all potential effects of automatic or unintended enabling of the power stage, for example, after power outage.
Implement all measures such as control functions, guards, or other safety-related functions, required to reliably protect against all hazards that may result from automatic or unintended enabling of the power stage.
Verify that a master controller cannot enable the power stage in an unintended way.

Failure to follow these instructions can result in death, serious injury, or equipment damage.

WARNING
	UNINTENDED EQUIPMENT OPERATION Set the parameter IO_AutoEnable to "off" if the automatic enabling of the power stage presents hazards in your application. Failure to follow these instructions can result in death, serious injury, or equipment damage.

Degree of Protection when the Safety-Related Function STO is Used

You must ensure that conductive substances cannot get into the product (pollution degree 2). Moreover, conductive substances may cause the safety-related function to become inoperative.

WARNING
	INOPERABLE SAFETY-RELATED FUNCTION Ensure that conductive substances (water, contaminated or impregnated oils, metal shavings, etc.) cannot get into the drive. Failure to follow these instructions can result in death, serious injury, or equipment damage.

Protected Cable Installation

If short circuits and other wiring errors such as a cross circuit between the signals of the safety-related function STO can be expected in connection with safety-related signals, and if these short circuits and cross circuits are not detected by upstream devices, protected cable installation as per ISO 13849‑2 is required.

In the case of an unprotected cable installation, the two signals (both channels) of a safety-related function may be connected to external voltage if a cable is damaged. If the two channels are connected to external voltage, the safety-related function is no longer operative.

ISO 13849-2 describes protected cable installation for cables for safety-related signals. The cables for the safety-related function STO must be protected against external voltage. A shield with ground connection helps to keep external voltage away from the cables for the signals of the safety-related function STO.

Ground loops can cause problems in machines. A shield connected at one end only is sufficient for grounding and does not create a ground loop.

Use shielded cables for the signals of the safety-related function STO.
Do not use the cable for the signals of the safety-related function STO for other signals.
Connect one end of the shield.