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offered by limit switches, engineers must define the operational and alarming characteristics in some type of sequenceof-operation document. Controls may be hardwired to accomplish this which, in turn, may require additional interlocks and indications. More commonly, a PLC and possibly an HMI will be used for this purpose, so these will need to be programmed. After equipment is initially commissioned, the complete machine functionality must be thoroughly tested to exercise all possible operating conditions. This is performed to confirm basic operation and more-advanced timing conditions. Actuator automation can significantly help operational and maintenance personnel down the road, especially if the system is configured with sufficient diagnostics to indicate the trouble. The flip side of this is that sensing elements introduce additional maintenance concerns — as they may fail or drift out of adjustment. The bottom line is that pneumatic cylinder control and monitoring elements are a valuable addition but introduce
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certain costs which must be weighed against expected benefits. Hybrid approach To help contain costs, many designers pursue a hybrid approach to specifying actuator controls, especially when developing systems or subsystems that will be produced in quantity. When a piece of equipment is first undergoing development, engineers may tend to over-specify the instrumentation and put sensors in all possible locations. While the system is in prototype mode, this allows them full access to use the automation platform for tracking cycle times and other operational parameters. This helps fine-tune operation, adjust timing and troubleshoot problems. Once the machine is running as needed, however, designers can sharpen their pencils and evaluate exactly which position switches are required for operation and maintenance. During this valueengineering phase, unnecessary elements can be removed to lower costs while still providing the instrumentation needed for safe and reliable operation.
Pneumatic actuators are workhorses for many different types of machines. Whether manually controlled or operated as part of an automated system, there are many reasons to monitor actuator position and integrate this information into the control scheme. Careful attention to required physical and electrical characteristics will help designers choose the best fit for any application. FPW
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Positions Sensors for Hydraulic Cylinders - say goodbye to drilling pistons!
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SIKO Products Inc., Phone +1 (734) 426-3476, www.siko-global.com
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