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Frequently Asked Questions Section 1-4
Q. Does the motor need a chassis ground connection?
A. Yes, for several reasons. Most importantly, this provides protection in the
event of a short in the motor that puts a hazardous voltage on its housing.
Secondly, motors exhibit leakage current that increase with aging. Lastly,
a grounded chassis generally emits less electrical noise than an unground-
ed one.
Q. What type of motor is compatible with the Omron inverters?
A. Motor type - It must be a three-phase AC induction motor. Use an in-
verter-grade motor that has at least 800V insulation for 200V class invert-
ers, or 1600V insulation for 400V class.
Motor size - In practice, it's better to find the right size motor for your ap-
plication; then look for the inverter to match the motor.
Note There may be other factors that will affect motor selection, including heat dis-
sipation, motor operating speed profile, enclosure type, and cooling method.
Q. How many poles should the motor have?
A. Omron inverters can be configured to operate motors with 2, 4, 6, or 8
poles. The greater the number of the poles, the slower the top motor speed
will be, but it will have higher torque at the base speed.
Q. Will I be able to add dynamic (resistive) braking to my Omron MX2 drive
after the initial installation?
A. Yes, the MX2 inverter already has a dynamic braking circuit built in. Just
add the resistor sized to meet the braking requirements. For more informa-
tion, contact your nearest Omron representative.
Q. How will I know if my application will require resistive braking?
A. For new applications, it may be difficult to tell before you actually test a
motor/drive solution. In general, some application can rely on system loss-
es such as friction to serve as the deceleration force, or otherwise can tol-
erate a long decel time. These applications will not need dynamic braking.
However, applications with a combination of a high-inertia load and a re-
quired short decel time will need dynamic braking. This is a physics ques-
tion that may be answered either empirically or through extensive
calculations.
Q. Several options related to electrical noise suppression are available for the
Omron inverters. How can I know if my application require any of these
options?
A. The purpose of these noise filters is to reduce the inverter electrical
noise so the operation of nearby electrical devices is not affected. Some
applications are governed by particular regulatory agencies, and noise
suppression is mandatory . in those cases, the inverter must have the cor-
responding noise filter installed. Other applications may not need noise
suppression, unless you notice electrical interference with the operation of
other devices.
Q. The MX2 features a PID control. PID loops are usually associated with
water control, flow control processes, heating, or process industries in gen-
eral. How could the PID loop feature be useful in my application?
A. You will need to determine the particular main variable in your applica-
tion the motor affects. That is the process variable (PV) for the motor. Over
time, a faster motor speed will cause a faster change in the PV than a slow
motor speed will. By using the PID loop feature, the inverter commands the
motor to run at the optimal speed required to maintain the PV at the de-
sired value for current conditions. Using the PID loop feature will require an
additional sensor and other wiring, and is considered an advanced appli-
cation.
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