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Frequently - ask Questions |
| Q. |
How
do I close an analog position loop without a digital drive? |
| A. |
Use
a linear analog feedback (a potentiometer for example) and connect
it to the feedback input of the amplifier. Connect your position
command to the reference input. Then convert the amplifier to
Current Mode and adjust the gain for best position accuracy. |
|
| Q. |
What
is the difference between PWM and Direction control, and Step
and Direction control? |
| A. |
PWM and Direction is a digital method of transferring analog
information. It is mainly useful when optical isolation is required
between the source of the command and the amplifier. Step and
Direction is a position control method and it requires a position
controller on top of the analog amplifier. |
|
| Q. |
We
have an existing design that uses a linear amplifier with a
bipolar power supply. Can we use the same power supply for a
PWM amplifier? |
| A. |
The
PWM amplifier requires a unipolar power supply. This means that
the bipolar power supply is wasted when used with a PWM drive.
If you insist on using your bipolar supply with a PWM amplifier,
pay special attention to the circuit common connection and common
mode issues. You may be required to isolate your reference command.
|
| Q. |
What
is preferred for better speed control:
a low-voltage tachgenerator or a high-voltage tachogenerator?
a low-inductance tachogenerator or a high-inductance tachogenerator? |
| A. |
Higher
voltage and lower inductance is preferred for servo performance
with a tachogenerator. |
| |
| Q. |
I
have a voice coil motor that has only two leads (like a brush
motor) but has no brushes. Should I use a brush or a brushless
drive for this type of motor? |
| A. |
Despite
the fact that the voice coil motor is a "brushless drive",
you can use a standard brush drive with it. |
|
| Q. |
Can
we drive a brushless motor that has an optical encoder only
but no Hall sensors? |
| A. |
There
are many optical encoders in the market that provide the "Hall
sensor signal" through optical channels. If your encoder
is one of these, just treat these outputs as if they are Hall
sensors and connect them to what is defined in the amplifier
literature as Hall inputs. |
|
| Q. |
Can
we control the speed of a brushless motor with Hall sensors
only? |
| A. |
Yes
you can. Elmo has achieved 200:1 speed regulation with Hall
sensor speed control using inexpensive analog drives. |
|
| Q. |
What
is better: a trapezoidal or sinusoidal brushless drive? |
| A. |
A
good trapezoidal drive is a less expensive drive and it will
satisfy most applications, especially the point-to-point ones.
The sinusoidal drive is more expensive and is required for better
low speed smoothness. |
|
| Q. |
What
is better: an optical encoder or a Resolver? |
| A. |
The
resolver withstands a harsh environment better but its R/D circuit
is expensive and it is also bandwidth limited. The optical encoder
is more fragile than the Resolver but it performs better for
servo applications and is also less expensive. |
|
| Q. |
Why
do we want to use digital drives? |
| A. |
Although
digital drives are more expensive, they are friendlier than
analog ones and have excellent long-term stability. Also, their
serviceability is far easier than analog drives. |
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