Frequently Asked Question

CANopen Safety sensor sends output with SRDO. SRDO stands for Safety-relevant data object. It is the only mechanism to transport safe data in an CANopen network.

An SRDO shall be transmitted cyclically. The cyclic transmission is monitored. An SRDO may be transmitted event-driven in addition to the cyclic transmission, if required.

Two types of SRDOs are distinguished: 

— the SRDO producer shall be used to transmit SR application data

— the SRDO consumer shall be used to receive SR application data

Our sensor works as an SRDO producer.

To enable safe transmission via CAN, a SRDO has the following properties:

• A SRDO consists of 2 CAN messages.

• The safety-related information is transmitted redundantly, with the data being inverted in the second CAN message.

• The SRDO CAN identifiers discriminates themselves in 2 bits.

• The CAN identifier of 1st CAN message is always odd, the CAN identifier of the 2nd CAN message is always even.

• A SRDO is sent cyclically. The refresh time determines the period. 

The SRDO refresh time and SRVT can be configured with object 1301h. The SRDO refresh time should always be smaller than the SCT (Safeguard Cycle Time) by the receiver. 80ms is the default and the recommanded value for our sensor due to the speed of the internal microcontroller. If the SCT is 50ms at the receiver, you will get an error.

SRVT should always be smaller than SCT, otherwise you will get an error. 

Reference:

https://www.can-cia.org/fileadmin/resources/documents/conferences/2017_rupprecht.pdf