6.3.5.2 Speed Monitoring
The monitoring starts when the SSM function is requested and becomes active. The monitoring of the maximum speed is specified
in EN IEC 61800-5-2. The monitoring of the minimum speed is an extra feature that is not specified by the standard.
Speed
t
SSM Max Limit
SSM Min Limit
SSM Output
SSM td2
SSM td2
Illustration 63: The SSM Function with Monitoring of Both the Speed Limits. The SSM Function is Requested During the Sequence.
It is possible to disable the monitoring of a speed limit by setting its monitor value to 0 rpm. However, if the monitoring of the
maximum speed is disabled, the SSM function cannot monitor excess speed.
The behavior of the function is the same for both the speed limits. See also 6.3.5.3 The SSM Safe Output.
Speed
t
SSM Min Limit
SSM Output
SSM td2
SSM td2
Illustration 64: The Minimum Speed Monitoring. The SSM Function is Requested During the Sequence.
N O T I C E
The SSM function does not report a violation if the speed goes outside the range that is defined by the speed limits. Only the safe
output signal indicates the situation.
Unlike other safe monitoring functions, the monitoring of the SSM function does not stop when a violation occurs in another safety
function, or when the STO function becomes active. The SSM output and the SSM signals are updated throughout the violation
situation and during the standstill caused by the STO function.
6.3.5.3 The SSM Safe Output
The state of the SSM safe output is determined by the speed of the motor and whether the SSM function is active. The table below
shows the state of the SSM safe output and the SSM Reached signal that corresponds to the output state.
AQ319736045637en-000101 / DPD01798104 | Danfoss A/S © 2021.06
Safety Functions
VACON® NXP Advanced Safety Options
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