For DC motors if the nominal load is given how would you sel

For DC motors, if the nominal load is given, how would you select a motor for a low duty cycle operation (i.e. the blood pressure monitor). How about selecting a motor for continuous operation? Why?

Please have a written response

Solution

There are few basic steps which you need to consider before selecting a DC motor for any sort of use:

1.Key criteria for selecting a DC motor includes first finding out what voltage is readily available for the application and what physical size the motor needs to be. Speed and torque can then be considered once these first two parameters are determined.

2. Voltage availability is a critical element in motor selection. Remote applications or portable devices, for example, are battery operated, while many rack-mounted devices and tools operate from a 24V power supply. DC motors are available for use at voltages as low as 1.5V and as high as 48V dependent on required power.

3. Physical size is often one of the limiting factors in motor selection because more and more applications have smaller footprints, like desktop 3D printers, portable medical devices, and hand tools. Often a compromise needs to be made between which motor to use and the available space it needs to fit into. Efficiency becomes a primary concern when you need to worry about power consumption to maximize battery life in a surgical tool or unmanned security drone.

4. As mentioned before, torque and speed also have an effect on motor frame size. High torque motors are often larger in size than their low-torque counterparts, which means that larger mounting hardware and larger housings may be an important machine requirement. For example, it takes a larger motor to rotate the magnets in an MRI than it does to run the windows in the doors of an automobile.

5. If your motor is going to operate at altitudes that are substantially above sea level, then it will be unable to operate at its full service factor because, at altitude, air is less dense and does not cool as well. Thus, for the motor to stay within safe limits of temperature rise, it must be derated on a sliding scale.

Up to an altitude of 3,300 ft, SF = 1.15; at 9000 ft, it declines to 1.00.