112
10
Appendix
10.1.4 Shielding Cables from the Field
Screening of leads from the field
Screened leads from the field (e.g. potentiometer leads) are best laid directly to the VMS (with-
out intermediate terminals).
Should intermediate terminals be necessary, the screening is also to be led immediately
alongside by the terminal. Long distances in the conduit without screening should be avoided.
10.2
Feedback at Three-Point-Step Channels
10.2.1 Connect with Positive Locking
Since the VMS, in the case of three-point step channels, adjusts the damper until the actual
value is equal to the setpoint value, the feedback potentiometer must always reliably corre-
spond to the damper position.
The damper motor potentiometer connections must be positive interlock connections, i.e. not
able to rotate.
In addition you must use potentiometers with high quality standards (see next page). If one of
these two points is not given, you must use two independent potentiometers (not dual-operat-
ed potentiometers) per channel for the feedback.
The motor damper connection must always be a positive interlock.
WARNING!
The connection has to be designed in that way that the maximum torque of the motor could
not break the connection under any condition.
Fig. 10-1 Example of positive potentiometer connection
10.2.2 Fail-Safe Feedback
In the case of single-channel feedback of TPS outputs, only authorised potentiometers may
be used. These must be switched directly.
Summary of Contents for VMS 4
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