Electric Motor
Diagnostics
By: Brad Cone, Applications Engineer |
Electric motors provide the power for many pump,
fan, and compressor applications. Speed, motor current and bearing temperature
are routinely measured. Bearing temperature is an excellent indication of
wear. Monitoring the temperature facilitates predictive maintenance
schedules.
Speed and motor current are used in motor control and may also be used to
provide safety shut down. The sensors that are used to monitor these
variables produce very different signals. Proximity sensors produce a
frequency signal that can vary from a couple of hundred millivolts to 24 Volt
amplitude pulses. Thermocouples and RTDs are used to measure
temperature. Thermocouples produce a small millivolt output. RTDs
are measured by supplying a constant current to the RTD. The current has
to be small to keep from heating up the element, hence another millivolt
signal. Motor currents can be very large. Getting all these signals
in to a control system can be problematic. |
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Action Instruments signal conditioners provide a
solution to normalize signals into a control system. Control systems that
accept a 4-20 mA signal are plentiful, therefore
less expensive. The frequency signal can be conditioned using a
Q476. The temperature, whether a thermocouple or an RTD can be
conditioned by a Q486, The motor current can be brought into a control as
a 4-20 mA by first using a current transformer to reduce the current to 5 amps
AC, then employing a C006, 0.1 ohm shunt resistor across the input of a G468 or
an AP6380. Both can be mounted on a DIN rail adjacent to the Q476 and
Q486.
Action Instruments isolating signal conditioners, we also have the package and
the power to meet your requirements. |
