Toshiba S2E21 - Page 69

TOSHIBA
6F9EOlll
01(t) and 6'2Ct.j represent the motor temperature rises, which can be
determined by measuring the motor winding temperature and the ambient
temperature using the RTDs. B (It) is determined by the motor current.
The S2E21 receives signals from the three RTDs in the winding at its inputs
RTDl, RTD2, and RTD3 and also the ambient temperature at RTD8 to determine
the heating time constant and the cooling time constant from the motor
temperature rises. The accuracy of calculating these time constants is
about *10X.
From equation (I). the heating time constant is expressed as
TR = -
t2 - tl
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
e (It) - eiw
(1')
‘ " ‘e (It) - e k2)
From equation (2). the cooling time constant is given by
t2 -. t,
TD=---
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ezct,j
(2')
--
Ln 02M
At each start and stop of the motor, the heating time constant and the
cooling time constant are detected over a length of time equivalent to
these time constants.
Five measurements are taken and averaged to determine
the heating time constant and the cooling time constant.
[Requirements for detecting the heating time constant]
- The olotor is sufficiently cool.
- The olotor current--is large enough (not too lightly loaded).
- The nlotor is n~t'?Cerloaded.
[Requirements for detecting the cooling time constant]
- The motor is sufficiently heated.
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