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HMI Flashcards

1
Q

AC Drives covert incoming DC to a AC bus? True or False?

A

False: AC drives convert incoming AC to a
DC bus

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2
Q

What are parts 4 of an AC Drive?

A

Input 3 phase - Rectifier Circuit - DC bus - Inverter Circuit - Motor

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3
Q

What does the DC bus use to filter current?

A

Large Electrolytic capacitors

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4
Q

Do AC drives use pulse width modulation?

A

Yes

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5
Q

What happens is the bleeder resistor blows up/not work?

A

The capacitors will not discharge? This can mean lethal voltages may be present hours after drive is locked out

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6
Q

What do you need before servicing an AC Drive

A

-Wear correct PPE,

-Before locking out drive measure and actually see the DC bus voltage go to 0

-lock out at disconnect

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7
Q

What does an AC drive use for its inverter circuit?

A

Transistors or IGBT devices are used to switch the DC bus on and off to the motor

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8
Q

What is the term “Motoring”?

A

When a motor is controlling the speed of a load

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9
Q

What is the term “Regeneration”?

A

When the load causes the rotor to rotate faster than the rotating field

  • The motor turns into an alternator and generates voltage back to the drive
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10
Q

What are 2 ways to avoid “Regeneration”?

A

Oversize the motor/drive combination

or

Dynamic Braking

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11
Q

What is does “Dynamic Brake” consist of?

A

A sensor to detect a rise in DC bus voltage. The sensor energizes a relay

One or more high wattage resistors that are connected across the DC bus by the relay contacts

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12
Q

How does “Dynamic Brake” work in an AC drive?

A

If the voltage in a DC bus rises, a sensor picks it up. This energizes a relay that connects high wattage power resistors to limit the current (use excess energy into heat).

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13
Q

Does “Dynamic Brake” only work is the load is slowed down?

A

No, if load is too fast it drags the rotor faster than the synchronous field rotation and causes regeneration

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14
Q

What stop config is this: Typically used to slow down conveyor type loads

A

Ramp to stop

  • Ramp to 0 following the Decel curve
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15
Q

What stop config is this: Used for fans and pumps

A

Coast to stop

  • turn off power
    immediately
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16
Q

What stop config is this: Drive applies a DC voltage and “locks” the rotor

A

DC Brake

  • applies a DC
    voltage to the stator
    -Can stop the load quickly but may
    also overheat the motor
17
Q

What stop config is this: Heavily loaded conveyors with high inertia

A

Ramp then DC Brake

18
Q

Which mode is for safety?

A

Coast to stop with magnetic clutch

19
Q

What is the equation for S-Curve time?

A

Scurve time = Accel or Decel time + S-Curve setting in percentage

20
Q

What is the equation for total accel time if there is an S-Curve applied?

A

Total Accel Time = Accel time + Scurve time

21
Q

What are parameters?

A

Storage Locations in the memory of an AC Drive

22
Q

What can parameters be (Data type wise)?

A

Single bit, a byte, an integer value or a 32 bit value

23
Q

What are parameters used for?

A

 They match the drive to the incoming
AC
 They match the drive to the motor
 They match the drive to the load
 They provide operating information
such as Load Current Being Drawn By
the Motor

24
Q

What is accel time parameter?

A

The parameter that defines how long it will take the drive to ramp from 0 hz to maximum frequency

25
Q

What is decel time?

A

how long it will take the drive to slow down to 0 frequency

26
Q

True or false: The preset frequencies could be
selected using hardwired controls
or through network control

A

True

27
Q

Some facts

A
  • The Allen-Bradley 1305 AC drive
    had approximately 70 parameters
  • The AB PowerFlex70 has
    approximately 400 parameters
28
Q

What are encoders?

A

Encoders are devices which are
coupled to the shaft of a motor (DC or
AC) and generate a series of square
waves proportional to rotational
speed

Encoders typically offer some
variation of a binary count – 512
square waves per 360 degrees
rotation, 1024 and so on

29
Q

How does an encoder detect direction?

A

They use “windows” which are mechanically offset by 90 degrees. If the motor is going CCW, light will pass through from LED A before LED B

30
Q

How many wires does an encoder use? What are they?

A

5 wires

A, ANOT - 180 degrees out of phase with A
B, BNOT - 180 out of phase with B
Z - homing shaft
VDC
DC COMMON

31
Q

What speed references do most AC drives allow to be used?

A

-Built in potentiometer
- External 0 to 10v DC
- External 4-20 mA signal
- Network Command (Ethernet)
- Motor Operated Potentiometer
- Pulse Train
- Preset Frequencies

32
Q

Analog References examples?

A

DC voltage or Current

33
Q

What do majority of conveyor controlled by AC drives use for speed control?

A

Preset Frequencies

34
Q

Where are Motor Operated Potentiometers used?

A

Common in industries where a film like substance (paper, steel, aluminum foil etc) is pulled through motor driven rollers

Offers “Speed Up” and “Slow Down” buttons that change drive
frequency

35
Q

What can parameter P038 do?

A

Set which speed reference to use

36
Q

What can parameter A051 do?

A

determines what function
digital in 1 causes the drive to do
 It can be set to the value shown to
accomplish a different purpose:
 1 Follow Accel 2 and Decel 2 curve
 2 Use an external hardwired Jog
 3 Cause an Aux fault (fault the drive
on purpose)
 4 Run at a preset frequency
 6 Use Comm port data (Ethernet,
DeviceNet, ControlNet)
 7 Digital in 1 will clear a fault
 8 Causes a Ramp to Stop
 9 Causes a Coast to Stop
 10 Causes a DC braking voltage to be
applied to the motor

37
Q

How does AC drives control speed of AC Motor?

A

Ac drives vary the frequency applied to a 3 phase AC Motor - Vary the frequency vary the speed

Must also vary voltage or the motor will be destroyed

38
Q
A

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