S7 MOTOR STARTING 4. SETPOINT PROGRAMMING
4-48
TIME BETWEEN STARTS
A motor start is assumed to be occurring when the SR469 measures the transition of no motor current to some value of motor current.
At this point, the Time Between Starts timer is loaded with the entered time. Even unsuccessful start attempts will be logged as starts for
this feature. Once the motor is stopped, if the time elapsed since the most recent start is less than the Time Between Starts setpoint, a
block will occur. If a block occurs, the lockout time will be equal to the time elapsed since the most recent start subtracted from the Time
Between Starts setpoint. A value of 0 effectively disables this element of the Jogging Block feature.
EXAMPLE:
Time Between Starts is programmed = 25 min
a start occurs at T = 0 min,
the motor is stopped at T = 12 min
a block occurs
the lockout time would be 25 min -12 min = 13 min.
4.8.4
RESTART BLOCK
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FUNCTION:
The Restart Block feature may be used to ensure that a certain amount of time passes between stopping a motor and restarting that
motor. This timer feature may be very useful for some process applications or motor considerations. If a motor is on a down-hole pump,
after the motor stops, the liquid may fall back down the pipe and spin the rotor backwards. It would be very undesirable to start the motor
at this time. In another scenario, a motor may be driving a very high inertia load. Once the supply to the motor is disconnected, the rotor
may continue to turn for a long period of time as it decelerates. The motor has now become a generator and applying supply voltage out
of phase may result in catastrophic failure.
Note: The Restart Block feature is strictly a timer. The SR469 does not sense rotor rotation.
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