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What Is Actuator Sizing?

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  • Written By: Paul Scott
  • Edited By: E. E. Hubbard
  • Last Modified Date: 04 September 2016
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    Conjecture Corporation
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Actuator sizing is the practice of correctly matching new or replacement actuators to their operating environment and to the devices that they actuate. This procedure is of critical importance if efficiency is to be maintained, devices are to function correctly, and losses due to damage are to be avoided. The process generally consists of choosing an actuator that will be mechanically suitable in terms of mountings, shaft sizes, and output specifics. The output of the actuator must also be considered to ensure that it is suitable for the application's torque, actuation type, and movement range requirements. Matching existing control and power source voltages are another of the critical considerations involved with actuator sizing.

When actuators are replaced or new installations planned, one of the first steps in the process is actuator sizing. This exercise ensures that the actuators chosen will work efficiently and economically without suffering damage or damaging the actuated device. If a damaged actuator is being replaced, the exercise is relatively simple, as the actuator details are known. This is, of course, if incorrect actuator sizing did not cause the old device to fail in the first place.

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When new installations are planned or an existing actuator assembly is being upgraded, a thorough actuator sizing exercise should be embarked upon. This typically involves considering several relevant areas, including mounting and drives, power ratings, and electrical requirements. Mounting and drive requirements are critical details although generally fairly simple to establish. Actuator casing mounting points should be compatible with those of the installation mountings, and output shafts must fit power transfer mechanism both in terms of sizing and connection types. In this regard, points such as mounting hole numbers, sizes, and configurations must be checked, as well as drive transfer coupling types, keyway details, and shaft sizes.

One of the most important, and complex, of the steps in correct actuator sizing is the establishment of correct power ratings. Many actuated devices feature mechanisms that require a range of torque inputs during operation. For example, the torque required to turn a large ball valve is usually significantly lower than that required to seat it. When considering the power output of a potential actuator, a sound knowledge of the total power requirements of the actuated device is thus needed.

Output type of new actuators is fairly easy to establish — a rotary actuator will obviously do no good where a linear output is required. The extent, or range, of that movement is, however, a far trickier issue. If a replacement or new actuator's output range is a little longer than required, damage to the actuated device and actuator is inevitable. If it is too short, the actuated device may not function correctly or could cause losses in production or process efficiency.

Control specifics are the last of the critical actuator sizing steps. Existing systems will typically feature established supply voltage and control protocol standards to which the actuator must be matched. A 110-volt actuator motor will have a service life measured in milliseconds if connected to a 500-volt power source, so these issues should receive close attention during the actuator sizing process.

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