Use Sto - Servotronix CDHD2S User Manual

Troubleshooting
A 24V power supply must be used. The power supply device must comply with the PELV/SELV
requirements stipulated in the EN60204-1 standard Safety of machinery — Electrical equipment of
machines Part 1: General requirements.
Note: The built-in 24V DC power supply of the CDHD2S is not approved for safety applications
and is therefore prohibited from being used as an STO power supply.
STO cable
According to the EN61326-3-1 standard, the STO cable length must be less than 30 meters.
Shielded and double insulated cable must be used. Double insulation refers to the need for
cable sleeves on supply wires. Cable sheathing must be connected to the power ground.
The optimal size of cable is 22AWG (0.34mm2). Since the current consumption of the STO
circuit is less than 0.25A, 24AWG (0.25mm2) is also suitable.
STO cable must be spatially isolated from any source of environmental stress, whether
mechanical, electrical, thermal or chemical.

9.5 Use STO

STO behavior
In accordance with the STO specifications specified in the IEC61800-5-2 standard, the STO
function is specially used to provide safe stop of motion system. Triggering STO function causes
the power supply of the motor control circuit to be removed, thus making the motor out of control.
When STO is triggered during the motor movement, the motor shaft and its connected mechanical
components slide until it stops moving by its own friction.
The immediate effect of STO is that the drive cannot provide any energy generated by torque.
STO can be used in the case that the motor is planned to come to a standstill in a sufficiently short
time based on load and friction, and in the application where the motor coasting and deceleration
will not have any impact on safety.
The figure below shows what will happen to the motor when the STO function is active. The
figure depicts that the motor is driven in constant speed mode, and when the power supply of STO
circuit is removed, the motor coasting stops.
The figure shows the motor velocity according to time. The behavior of the motor when it is
controlled to stop (STO function is not effective - VCMD and V trace) and coasting to stop (STO
function is effective - reference trace) is compared.
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