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Reference Manual
00809-0100-4696, Rev AA
September 2004
Rosemount 848L
E-8
Winding Temperature The multi-rung delay mechanism above may be replaced if the motor has a
winding temperature sensor and a convertor that opens a contact when the
motor is too hot and closes when it is sufficiently cool. The following drawing
applies such a contact (as input 4) to the Restart Delay diagram, which
reduces it to a permissive circuit.
| |
| 1 2 4 Out1 |
+--| |--+--||----||--+----------------( )--+ OUT1_EQ
| | | |
| | 3 | |
| +--||--------+ |
| |
The equations for a permissive circuit have already been described.
• The expression is AND(IN(1),OR(AND(IN(2),IN(4)),IN(3));
NOTE
This is not an interlock for high winding temperature. That is taken care of by
the overloads. The purpose of this circuit is to prevent starting if the motor is
too hot, such that the heat generated by starting would exceed the
temperature rating of the motor. When the motor starts, the temperature will
rise and open the safe temperature contact. This will happen after the
auxiliary contact has closed, so the motor will continue to run. As it runs, it is
cooled by an internal fan and eventually the safe temperature contact closes.
An interlock could be added, but the temperature would have to be set much
higher than the safe restart temperature.