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Safety Manual for DEN-XCR

This product is certification pending. Until receiving the certificate any content in this section is subject to change.

Revision History







First official release of the document.

R. Picas

J. Fernández


Formatting updated. Multiple content updates:

  • Voltage thresholds and Reaction times updated.

  • Integration Requirements clarified.

  • Environmental Conditions slightly modified.

  • External Diagnostic Test procedure optimized.

R. Picas

J. Fernández


PFH and MTTFd values updated

R. Picas

J. Fernández


This document defines the DEN-XCR Safety Specifications and the Integration Requirements that must be fulfilled to guarantee Functional Safety.

Safety Concept

The DEN-XCR is a product of the Novanta Summit Safety Series, a family of servo drives with Functional Safety capabilities. The product consists on an Summit Servo Drive with a hardware-implemented STO function.

The Safe Torque Off (STO) is a safety function that prevents motor torque in an emergency event while DEN-XCR remains connected to the power supply. When STO is activated, the power stage is disabled by hardware and the drive power transistors are disconnected, no matter what control or firmware does. The motor shaft will slow down until it stops under inertia and frictional forces. Although not common, in the event of a failure of the power stage during an STO situation, the maximum expected motor movement with torque can be up to 180º electrical degrees. The system must be designed to avoid any hazard in this situation. STO safety function is only considered when the drive is controlling three-phase permanent magnet synchronous rotating motors. STO does not apply to DC brushed motors. 

If the STO inputs are not energized, the transistors of the power stage are turned off and an STO fault is notified. In order to activate the power stage, and therefore allow the motor operation, the two STO inputs must be energized (high level). STO inputs should not be confused with a digital input configured as enable input, because enable input is firmware controlled and does not guarantee intrinsic safety as it can be reconfigured by a user.

In order to ensure redundancy and safety, the DEN-XCR includes 2 separate STO inputs that must be activated or deactivated simultaneously. A difference of state between \STO_A and \STO_B inputs will be interpreted as an abnormal situation and trigger a fault. After some time, the abnormal fault will become latching and require a power supply reset. 

Safety Specifications

Safety Function

Safety relevant parameters according to IEC 61508:2010

(certification pending)

Safety relevant parameters according to EN ISO 13849-1:2015

(certification pending)

Safety Function Reaction Time

Safe Torque Off (STO)

The function prevents rotating torque from being provided to the motor.

Safety integrity level: SIL3

PFH: ≤ 1.12 x 10-9 1/h

SFF: ≥ 99 % (High) 

Performance Level: PLe

Category: 3

MTTFd ≥ 100 years (High) 

DCavg: 99% High

tSF ≤ 13.5 ms

The Safety Function Reaction time is measured as the time since one of the STO inputs (\STO_A or \STO_B) goes below VIL and the STO function actuates (power transistors deactivated). 

Safety Specification


Command Source

Safe Inputs

Standards compliance 

Targeted standards (certification pending):

  • EN 61800-5-2:2017

  • EN 61508:2010

  • EN ISO 13849-1:2015

Fault Reaction Time

≤ 13.5 ms

System maximum Reaction Time in case of a Detected Fault or safety function activation.

High-demand mode

The EUC (Equipment Under Control) is considered as a high-demand or continuous demand mode system.

Mission Time

The mission time of the EUC is of 20 years.

Diagnostic Time Interval 

In order to guarantee the correct operation of the safety functions, the user must execute the External Diagnostic Test (see further information below) regularly.

The diagnostic test interval is defined as a minimum of 1 activation per 3 months. 

Included Diagnostics

  • Internal power supply voltage monitors. 

  • Abnormal STO Input

  • Latching Abnormal STO Input: dual-channel values mismatch for a long period of time

Status of STO_A, \STO_B, ABNORMAL_FAULT, and SUPPLY_FAULT can be read from the communications.

STO firmware notification

A STO stop is notified to the motion controller and creates a fault that can be read externally from any communication interface, however, STO operation is totally independent and decoupled from control or firmware. 

External Diagnostic Test

The operation of the STO diagnostic circuits must be verified at least once per 3 months. The following procedure details a method to verify the STO diagnostic circuits and the external wiring. If the procedure results are not the expected ones, safety could be violated and the system cannot be used. Note that it is responsibility of the customer to prevent any hazards related to motor movement during this proof test. 

The procedure requires the drive to be connected to a motor. 

Procedure Step



Power on the drive.


Transition to a normal operation state where the power stage can be enabled, allowing motor rotation.


Activate the Safety Function by providing:

  • \STO_A = low

  • \STO_B = low


Remain in this state more than tABN_LATCH_MAX seconds (see Interface and Integration Requirements).


Deactivate the Safety Function by providing:

  • \STO_A = high

  • \STO_B = high 


Without performing a power reset, verify that the power stage can be enabled, allowing motor rotation.

From Motionlab 3 software or communication channel, check that no Abnormal Fault appears.

Interface and Integration Requirements

The following table details the Interface and Integration Requirements that guarantee Functional Safety.

Integration Requirement


STO Inputs Interface electrical characteristics

Input pins


Number of independent channels


Type of Inputs

Isolated inputs (\STO_A, \STO_B) with common reference (STO_RET).


Digital inputs with ESD protection.

Maximum input LOW level (VIL)

5 V (below this value the \STO is ACTIVE).

Minimum Input HIGH level (VIH)

15 V (above this value the \STO is INACTIVE).

Maximum absolute ratings

  • Vmax_nom (maximum nominal voltage)= 32 V SELV

  • Vmax_fault (maximum voltage in the event of an external failure) = 60 V

Max. Input current

  • ≤ 8 mA @ 32 V input

  • ≤ 15 mA in case of internal failure.

Isolation Level

> 4 GΩ, 500 Vrms, 1000 VDC

ESD capability

IEC 61000-4-2 (ESD) ± 15 kV (air), ± 8 kV (contact)

STO Interface Timing Characteristics

STO reaction time (activation time)

tSF ≤ 13.5 ms

The Safety Function Reaction time is measured as the time since one of the STO inputs (\STO_A or \STO_B) goes below VIL and the STO function actuates (power transistors deactivated). 

STO deactivation time

tSTO_DEACT ≤ 10.5 ms

The STO Deactivation time is measured as the time needed for deactivating the HW STO from a VIL= 5 V when activated with with VIH ≥ 15 V. 

Max. activation pulse filtering (OSSD)

tpulse ≤ 1 ms

See OSSD Pulse Filtering diagram.

Abnormal STO diagnostic time

tABN ≤ 13.5 ms

Minimum STO signals discrepancy time that causes an Abnormal Fault and activates the Safety Function.

Max. abnormal STO latching time

tABN_LATCH_MAX ≤ 2.5 s

Minimum STO signals discrepancy time that guarantees a latching Abnormal STO Fault.

Min. abnormal STO latching time

tABN_LATCH_MIN ≥ 0.6 s

Maximum STO signals discrepancy time that guarantees that Abnormal STO Fault is not latched.

Power Supply Voltage Range

48 V SELV (range from 8 V to 60 V; maximum failure voltage 60 V)

OSSD Pulse Filtering

The following diagram depicts the \STO_x signals when using pulse filtering for OSSD.

STO Operation States

The truth table of the STO inputs is shown next indicating the different states of the system:



\STO_A status / level

\STO_B status / level

Power stage status

STO report bit status

STO abnormal fault

State description

Normal operation

STO Enabled
(No torque to the motor)








The system logic is powered, but the STO function is activated. Therefore, no torque can be applied to the motor.  

STO trip is reported to the MCU and to the safety circuitry. This is intended safe torque off with dual-channel operation.

Torque enabled

(STO inactive)





Can be enabled



The STO function is deactivated, and torque can be provided to the motor. The motor can run under firmware control. This is the normal operation state. 

Abnormal operation

Abnormal STO 








If any issue is detected on the dual-channel STO function (the channels logic level is different), an Abnormal Fault is detected, activating the Safety function and reporting it via FW. This state avoids the application of torque to the motor.








Abnormal STO Latched








If the Abnormal Fault persists for ≥ tABN_LATCH_MAX, the fault becomes latching, maintaining the Safety Function activated until a power supply reset cycle.

Abnormal Supply 








If a voltage out of the limits is detected on the internal logic voltages, the system is conducted to a safe state, similar to power-off. Only if the safe logic voltages are recovered (usually after reparation or restart), the system can return to any other state.

\STO_A and \STO_B signals should always change at the same time with a maximum of tABN mismatch. This is necessary to have 2 channel redundancy and allow diagnostics, as a mismatch will cause an abnormal fault.

The logic level of an STO signal between VIL and VIH is unknown. If supplied at unknown level, \STO_A and \STO_B could have different logic values and trigger an abnormal latching fault.

In order to ensure this, do not add big capacitors (> 1 µF) in parallel to the STO inputs as this may cause faults during activation or deactivation of the STO.

Les signaux \STO_A et \STO_B doivent toujours changer en même temps avec un décalage maximum de tABN. Ceci est nécessaire pour avoir une redondance à 2 canaux et permettre le diagnostic, car une discordance provoquera une anomalie de fonctionnement.

Afin de garantir cela, n'ajoutez pas de gros condensateurs (> 1 µF) en parallèle aux entrées STO, car cela pourrait provoquer des défauts lors de l'activation ou de la désactivation du STO.

Le niveau logique d'un signal STO entre VIL et VIH est inconnu. S'ils sont alimentés à un niveau inconnu, \STO_A et \STO_B peuvent avoir des valeurs logiques différentes et provoquer une anomalie de fonctionnement.

Application and Environmental Conditions

Functional Safety can only be guaranteed in the following environmental conditions:

Motor Type

Functional Safety is only considered when the drive is controlling three-phase permanent magnet synchronous rotating motors. STO does not apply to DC brush motors. 

Uncontrolled Motor Movement

In the event of a failure in the power stage, the motor shaft may rotate up to 180º electrical degrees. It is the responsibility of the customer to prevent any hazards related to this unexpected motor movement.  

Environmental Conditions1

Pollution degree

Pollution degree 2 with an IP54 enclosure installation.

Over-voltage category 



< 2000 m above sea level.

Ambient Temperature (Operating)

-20 ºC to 60 ºC

Case Temperature (Operating)

-20 ºC to 70 ºC

Storage Temperature (Non-Operating)

-40 ºC to 100 ºC


10 Hz to 150 Hz, 1 g.

Test according to IEC 60068-2-6:2007-12: Test Fc


±5g Half-sine 30 msec 

Test according to IEC 60068-2-27:2008-02: Shock


Functional Safety has been tested according to IEC 61800-3:2018 procedures with the extended ranges of IEC 61800-5-2:2017.

To fulfill the EMC requirements the use of the following elements is required:

  • Input EMI filter.

  • Motor phases ferrite cable core.

  • Properly grounded aluminum enclosure. See grounding recommendations for further information.


The interface board must meet the following environmental standards:

  • IEC 60068-2-1:2007

  • IEC 60068-2-2:2007

  • IEC 60068-2-38:2009

  • IEC 60068-2-78:2012

  • IEC 60068-2-6:2007

  • IEC 60068-2-27:2008

1: The drive can operate outside this range as indicated in the Product Description , however, it will not meet Functional Safety requirements.

Wiring example

The following is a wiring example for the STO inputs.

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