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APPLICATIONS: Benefits of DC Motor Speed Sensing via Supply Current |
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| There are several
reasons to use DC motor supply current to measure motor speed, not just
because sometimes it is the only way. Yes, in some products, such as a
fuel pump or electric water pump, where you cannot access the motor, the
supply current is the only, and therefore the best method of measuring motor
speed. However, there are many other cases where motor current speed sensing
provides significant advantages over traditional sensors. |
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 Allow Complete Functionality of Final Assembly |
| Where DC
motors are embedded into a product, manufacturers need to be able to test
the end functionality whether the motors have been previously tested or not.
For 100% QC testing, the complete functionality has to be tested after
assembly. What if a screw fell into the works? It will
draw current, but will it pump fuel? If its hard to turn due to
bearing end-caps being too tight, will the motor burn out? Will it fail in
the field? What if the mechanisms that the motor are to drive are flawed?
CDA Systems Ltd. offers a few products
to allow final test of products with embedded DC motors. The
CRSM1 and CMSS56 products offer
a means of testing even the most challenging DC motor. These products
output an accurate, real-time speed readings that are not estimates.
The CMSS56
also provides accurate measurements of RMS, average, and peak-to-peak
current, along with simultaneous measurements on a secondary analog channel,
allowing monitoring of another process variable such as pressure or
vibration.
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Simpler Test
Cell |
| Some
devices, such as a power-seat motor can be mechanically coupled for testing
of the motor and assembly functions, or their speed can be measured with
optical or inductive sensors. However, these these can often be
difficult to implement. With one of CDA's motor speed sensors, the
device need only be powered up through a typical current shunt or
Hall-effect sensor, and the speed, RMS current, average current, and
peak-to-peak current are measured. |
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Lower
Maintenance Requirements for Test Cell |
| Using
current sensing to determine motor speed removes the requirement for precise
alignment of optical or inductive sensors. There is no requirement for
maintenance mechanics to constantly adjust and clean photo sensors to keep
the test cell operating at full capacity. There is no downtime due to
physically damaged sensors. In fact, the current shunt used as the
input sensor to the CDA modules could be safely located in a control panel
20 feet away.
--> A guaranteed reduction in
maintenance! <-- |
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Environmental
Testing Advantages |
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Automotive
manufacturers often have to wrestle with environmental test requirements.
For example, many manufacturers of engine cooling modules are required to
perform "Salt Spray" testing, where the modules are constantly subjected to
a spray of salt and/or salty water. While the engine cooling modules
can usually take the abuse, often the sensors used by manufacturers cannot.
Testing has to be stopped every few days to clean and re-align sensors.
Often, there are sensor failures in high-heat testing. If the motor
speed is measured via motor current, no such problems exist
--> A guaranteed
reduction in maintenance! <-- |
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(scope trace,
motor speed & current on startup) |
Enhanced
Analysis |
| CDA's
motor speed sensors update motor speed every time the motor commutates.
If there are 20 commutator segments in the motor, the speed is calculated 20
times per rotation. This allows more accurate characterization of
motor performance than can be done with traditional sensors.
Further,
the CMSS56 module also reports RMS, average, and peak-to-peak current, along
with measurements from a secondary analog channel and digital inputs.
Some of our customers have found innovative
applications for our motor speed modules, including using the tachometer
output as an input strobe for motor noise "order analysis". |
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Motor Speed
Control |
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CDA's motor speed sensors can be used
in applications where control of motor speed is important. In a
production test environment, could be for final balance/vibration checks on
assembled modules, or for performance testing. In control systems, the
applications for precise motor speed control are endless. The fast
response time, and variable output mechanisms of CDA's modules make them
perfect fits in control systems that use any of the following: |
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- Tachometer pulses - One pulse per
rev tach output
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- Analog voltages - Precision
analog output
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