BENSHAW RediStart MX3 Series, User Manual

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UTS Timer When the start mode is set to open-loop voltage ramp acceleration, the UTS Timer acts as an acceleration
kick. When the UTS timer expires, full voltage is applied to the motor. This feature can be used to reduce
motor surging that may occur near the end of an open loop voltage ramp start. If a surge occurs near the end
of the ramp, set the UTS timer to expire at this time and restart the motor. If the surge still occurs, set the UTS
time to a lower time until the surging subsides. If motor surging continues to be a problem, it is recommended
that one of the other standard MX
3
closed-loop starting profiles be used.
7.3.6 Tachometer Ramp Selection
Description The Tachometer control ramp profile provides a method to linearly ramp the speed of the system. When this
control mode is selected, the starter uses a tachometer to provide speed feedback to the starter. This mode is
commonly used on conveyor belt applications where a smooth controlled start is necessary under various load
conditions to prevent belt breakage, lifting, or excessive stretching. The Tachometer controller consists of an
inner PID current loop and an outer PI speed control loop.
z
NOTE:
The maximum current limit will override the speed control loop if necessary. If the Maximum
Current level is not set high enough or the load is too great, the MX
3
starter will limit the motor current to this
maximum level. When current limiting occurs, the speed profile will no longer be linear and the motor(s) will
take longer to accelerate to full speed. Therefore, if current limiting is undesirable, this parameter must be set
higher than the peak starting current during a linear speed ramp start.
Tachometer Requirements
In addition to the basic motor and starter setup variables, the following needs to done to use the tachometer
feedback control ramp:
1. Connect a tachometer with appropriate DC output voltage and correct polarity to the MX
3
power card input
(TB5-2 (+ positive) & TB5-3 (- negative)) .
2. The tachometer feedback Start Mode (CFN01) is selectable as “Tach Ramp” from the Starter Modes menu.
3. Program the appropriate variables in the Tachometer Setup menu.
FUN13- Tachometer Full Speed Voltage on page 130.
FUN14- Tachometer Loss Time on page 130.
FUN15- Tachometer Loss Action on page 131.
4. Set the Initial Current (QST06/CFN03) level to the desired starting current.
5. Set the Maximum Current (QST07/CFN04) level to the desired maximum current limit.
153
7 - THEORY OF OPERATION
Voltage
Time
Kick Time
Ramp
Time
Initial Voltage
Optional Kick
Current
Full Voltage
Start
command
UTS Time
Figure 43: Effect of UTS Timer on Voltage Ramp