eDrive - Summer 2017 - 8

Feature Article
motor replaced in the off chance one of them
gets damaged.

Stall Conditions

It is important to note that in each of the
different configurations, all three phases are
monitored. Not all motors have this setup because of the assumption that any overheating
in one phase would be evenly replicated in
the others. A case where this wouldn't apply
would be under stall conditions. In a machine
tool duty cycle, where torque motors are
commonly used, there may be an instance
where a part is held in place for a certain
amount of time and the current isn't evenly
distributed amongst all the phases. This is
called a Stall condition. If one phase is found
to be above an acceptable level and it's not
the one that has a sensor on it, then a user
runs the risk of a phase overheating without
the driver even being aware of it. This is why
monitoring all phases is important.

Figure 5. A 3-Phase Current Diagram. Note the Large Difference Between Phase 1
and 3 at Given Point

Performance Reduction

Usually when a project is in its prototyping
stages, not all of the demands of the applications are fully known. Because of this, when
the time comes to select a motor, sometimes
an option that has more power than what is
necessary for the application is selected. This
is usually done in order to allow room for any
unexpected forces that would cause the motor to overheat. Along with that, the motor
could be restricted from going past a certain
temperature that is well below its max, or not
Figure 6. Different Temperature Readings Over Time; Note the Delay in "Real Temp"
be allowed to reach its listed average current
value. This is because since there is a delay in
the KTY sensor output, these measures are put in place to anticipate overheating before the motor gets
damaged. The downside of these limitations is that the motor is unable to reach its full potential and
could be larger than what is necessary.
Depending on the level of how over-sized the motor is, it may turn out that another, smaller, and less expensive motor is able to complete the same task. If it is discovered that by letting a motor reach values
closer to its limit, a replacement can be chosen and end up saving a customer money in the long run.

IMTHP

In order to eliminate a lot of the safety measures that would limit the potential of a selected motor,
ETEL developed the IMTHP. The IMTHP is a thermal module developed for torque motors which takes the
inputs of the three KTY Sensors and provides a corrected analog temperature signal, allowing the user
to have a precise and continuous monitoring of the actual temperature in the motor. It then takes these
readings and uses its own algorithms to determine if the temperature is on track to reaching an overheating point by outputting a simple digital warning/error signal that can be used without complex data
processing on the controllers part, and have the machine properly react if any problem is ever detected.
This was developed as a way to overcome the delay in the KTY sensor reading so that an overall more
accurate and precise temperature reading could be monitored. The IMTHP also provides galvanic insulation to protect the machine cabinet in case of a critical overvoltage defect.
8

Summer 2017

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Table of Contents for the Digital Edition of eDrive - Summer 2017