Siemens SINUMERIK 828D Function Manual page 354

G2: Velocities, setpoint / actual value systems, closed-loop control
7.4 Setpoint/actual-value system
Each position measuring system must be referenced separately.
For an explanation of actual-value acquisition compensation functions, see:
References:
/FB2/ Function Manual, Extended Functions; Compensations (K3)
For an explanation of encoder monitoring, see:
References:
/FB1/Function Manual, Basic Functions; Axis Monitoring, Protection Zones (A3)
Switching between measuring systems
One can switch between the two measuring systems through the following NC/PLC interface signals:
DB31, ... DBX1.5 (position measuring system 1)
DB31, ... DBX1.6 (position measuring system 2)
References
/FB1/ Function Manual, Basic Functions; Various Interface Signals (A2)
It is possible to switch over measuring systems at any time, the axes do not have to be stationary to do this.
Switchover only takes place if a permissible deviation between the actual values and the two measuring systems
has not been violated.
The associated tolerance is entered in the machine data:
MD36500 $MA_ENC_CHANGE_TOL (Max. tolerance on position actual value switchover)
On switchover, the current difference between position measuring system 1 and 2 is traversed immediately.
Monitoring
The permissible deviation between the actual values of the two measuring systems is to be entered in the
machine data:
MD36510 $MA_ENC_DIFF_TOL
For the cyclic comparison of the two measuring systems used, this difference must not be exceeded, as
otherwise Alarm 25105 "Measuring systems deviate" is generated.
If the axis is not referenced (at least in the current control measuring system) then the related monitoring is not
active if MD36510 = 0 or if neither of the two measuring systems in the axis is active/available).
Types of actual-value acquisition
The used encoder type must be defined through the following machine data:
MD30240 $MA_ENC_TYPE (type of actual-value acquisition (actual position value))
Basic Functions
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Function Manual, 09/2011, 6FC5397-0BP40-2BA0