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Hazardous Area Stepper Motors -PT Frame Sizes
Hazardous Area Motors - Explosion Proof & Purged and Pressurized
Frame size families:
Empire Magnetics' PT Series Step Motors are sealed and equipped with air fittings for pressurization. With an optional temperature sensor, PT motors can be easily designed into a system which meets NFPA requirements for Class I, Class II and Class III hazardous locations.
In a typical installationsuch as spray painting, printing, flour mills, fuel processing, alcohol production, chemical processing or rocket fuel machiningthe motor is remotely located in a hazardous area. Air lines, power and temperature sensor cables run to the control station in a non-hazardous area. Protective conduit shields cabling from mechanical damage. At the control station, a temperature indicator with a setpoint alarm displays motor temperature. The setpoint alarm output will cut power to the drive if temperature exceeds the setpoint. A differential pressure switch on the return air line monitors motor pressure. If pressure fails, this switch also cuts power to the drive. When power is applied, the motor undergoes a purge delay period before being energized.
Frame size selection:
Motors are typically made in groups or families, the families are identified by the outer diameter or size of the square, these references are called frame sizes. In the American system, a 23 frame is a nominal 2.3 inches in diameter. For motors less than one inch in diameter, the reference is typically known as a size. Herein is a list of the frame sizes offered by Empire Magnetics Inc. and some of the characteristics of the group that will allow you to select from them.
Frame Size 11: Nominal outer dimension of 1.1 inches, these motors are very low power, suitable primarily for instrumentation applications. Torque range of .5 to 2.5 oz-in. Cylindrical shaped motor with square front flange.
Frame Size 17: Nominal outer dimension of 1.7 inches, these motors are relatively low power useful for a wide range of industrial applications. Torque range of 13 to 26 oz-in. Cylindrical shaped motor laminations, with square end flanges front and rear. Since this motor does not have a housing, it is not available in all environments.
Frame Size 23: Nominal outer dimension of 2.3 inches. Extremely popular size useful for a wide range of industrial applications. Torque range of 60 to 150 oz-in. Cylindrical shaped motor with square front flange.
Frame Size 34: Nominal outer dimension of 3.4 inches. Power range of 80- 240 watts, useful for a wide range of applications. Torque range of 150 to 450 oz-in. Cylindrical shaped motor with square front flange.
Frame Size 42: Nominal outer dimension of 4.2 inches. Power range of 240-700 watts, relatively high power in the stepper motor range. Torque range of 400 to 1600 oz-in. Cylindrical shaped motor with square front flange.
Products for use in Hazardous Areas
Automating an industrial process is a complex problem when combustible vapors or dust are present in the work environment.
Two commonly used methods are Explosion Proof (EP) and Purged and Pressurized (PT). Explosion Proof devices are intended to withstand and contain an expected explosion, Purged and Pressurized systems are intended to prevent an explosion from occurring. While Explosion Proof is more widely known the Purged and Pressurized technique is more flexible and universally recognized.
The National Fire Protection Association publishes "Purged and Pressurized Enclosures for Electrical Equipment in Hazardous Locations", (NFPA496), which describes the application of positive pressure with dry air or nitrogen to convert the interior of a motor to a non-hazardous area. A copy of the standard is available from the NFPA, (call 800/344-3555). Additional information is included in the National Electric Code, also written by the NFPA.
For applications and information, the following article may be of
Using Purge and Pressurization to Prevent Explosions
Empire Magnetics makes no claim as to the suitability of pressurized motors for any particular application. These products are not rated or warranted as Explosion Proof Motors, nor does Empire Magnetics assume any liability for their use in proximity to volatile materials. Responsibility for motor use lies solely with the user.
Each unit includes a ten foot cable. Cables up to 100 feet in length may be ordered. NPT cable penetration allows connection of conduit. Use of pressurized conduit is recommended. Motors are otherwise supplied with air fittings.