eDrive - Summer 2017 - 7

Feature Article
Temperature Sensors

There are many types of motor temperature
sensors used on the market but the focus
here will be on common ones that are also
used in ETEL torque motors. They are KTY,
SNM, and S01 sensors.

KTY

KTY sensors are silicon temperature sensors
that have a resistance values which changes
based on its temperature. The relationship
between the temperature in the windings
and resistance value the sensor outputs is
linear. Although KTY sensors are considered
the most accurate of the three mentioned,
one must compensate for a delayed response
since the change in resistance is not instantaneous enough to detect sharp changes in
temperature.

SNM

An SNM sensor is typically used in low-voltage circuits and is meant to be connected to
a controller working at an electronic voltage
level typically around 5 VDC. Like a KTY sensor, it outputs a resistance value based on the
temperature but the change is a lot sharper.

S01

An S01 sensor is a limit switch based on a bimetallic mechanism. It is a digital signal that
reads as either open or closed. If desired, it
would be able to directly cut off the power of
some electronics in case of overheating since
it operates as more of a "switch" rather than
having a temperature/resistance relationship.
It is able to operate in a medium to high voltage range of around 50 VDC.

Figure 3. Relationship Between Temperature and Resistance Value for an SNM Sensor

Sensor Configuration

There are two kinds of standard temperature configuration ETEL utilizes for its torque
motors. The first is Configuration 8 which
not only uses each type of sensor but has all
three phases monitored. Although the option
for having all three sensor types is available,
it is Configuration H that is recommended
since there is a spare set of KTY sensors on
each of the phases. The importance of this
comes from the fact that KTY sensors, while
the most accurate of the different types, are
Electrostatic-sensitive devices (ESD) and
there are many opportunities in the machine
assembly process where the sensors can be
damaged. Having an extra set ensures that
it wouldn't be necessary to have the entire
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Figure 4. ETEL's Sensor Configurations. Configuration 8 (Top) and H (Bottom)

Summer 2017 7

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