Safety stop mode

When a CANopen Safety sensor detects a failure, an emergency message is generated and a safety stop mode is activated. In the safety stop mode, no communication is possible(no SRDO, no TPDO, no Heartbeats), only by giving the sensor a new power cycle will restart the communication.

This is different than a NMT stop mode. By switching a CANopen device into the NMT state Stopped it is forced to stop the communication altogether (except node guarding and heartbeat, if active). And you can switch the sensor back to operational or any other mode without giving a new power cycle.

How to avoid false alarm?

1. You can increase the acceleration tolerance to make the sensor less strict with errors. 

The sensor consists of two accelerometer elements. The acceleration values of these elements are converted to angles. These angles are compared and a safe state is set when the elements differ too much. To prevent for false alarms, a tolerance can be configured. The tolerance consists of allowing an angle deviation during a certain time.

These values are adjustable via object 4006h sub- index 01h and 02h. The default values are 300d and 200d ( 3°during 2000 ms). The actual values used by the customer should fit the application involved. Before using this sensor and with the settings chosen the customer should evaluate risks in order to check whether the chosen settings satisfies his safety requirements. Manufacturer is not responsible for any damage caused by these customer-setting, even when the manufacturer defaults are used.

Definitions for the Redundancy error:
‘Redundancy Compare time’ (user programmable, default 2000ms)
‘Redundancy Compare angle’ (user programmable, default 3°)

2. Use Peak Suppression Filters (PSF) to reduce unwanted disturbances in the inclination
measurement caused by acceleration peaks.

Filter principle: as inclination normally changes relative slow, a sudden peak in the inclination signal indicates an acceleration peak instead of a real inclination angle change. In this case, the filter can make the sensor ignore this peak for a certain time.

PSF in the redundancy compare chain (object 4007h):
The redundancy compare chain checks the difference between the two redundant MEMS chips. The filter helps to prevent for false safety alarms.

PSF in the inclination output chain (object 4008h):
The filter in the output chain makes the inclination output more stable and more realistic

PSF can be adjusted with 2 parameters:
• Angle (°): This parameter sets the threshold for the peak. Only peaks above this threshold will be filtered. Setting this angle parameter to 0° will disable the PSF
• Time (ms): After the peak suppression filter becomes active, it will hold the inclination signal for a certain period of time, set by this parameter.

Default values for Object 4007h: on, 3°, 40ms
Default values for Object 4008h: on, 9°, 50ms