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Hardware Components for Automation and Process Control
Published in Stamatios Manesis, George Nikolakopoulos, Introduction to Industrial Automation, 2018
Stamatios Manesis, George Nikolakopoulos
Limit switches are cheaper in comparison to proximity or photoelectric switches, and thus may be preferred in any application where noncontact actuation is not required. There is also a wide range of limit switches regarding their size, from subminiature size for use inside small machines to heavy-duty ones for large mechanical systems. Furthermore, limit switches are available in a variety of rotary arm styles, operating forces, reset forces, over-travel distances, operation requirements, and environmental factors (including moisture, contamination, temperature, shock, and vibration). Limit switches have contacts with electrical ratings that are usually around 250 V AC and between 10 and 15 A. Some manufacturers of plug-in style limit switches offer switch bodies that have a LED or neon lamp status indicator. As with all other sensors, the actuation of a limit switch provides an electrical digital signal (change of contact state) that causes an appropriate control system response.
Digital Transducers
Published in Clarence W. de Silva, Sensor Systems, 2016
Digital binary transducers are two-state sensors. The information provided by such a device takes only two states (on/off, present/absent, go/no-go, high/low, etc.) that can be represented by 1 bit. For example, a limit switch is a sensor that is used in detecting whether an object has reached a particular position (or limit) and is useful in sensing presence/absence and in object counting. In this sense, a limit switch is considered a digital transducer. Additional logic is needed if the direction of contact is also needed. Limit switches are available for both rectilinear and angular motions. A commercial limit switch is shown in Figure 11.15. This can detect an object reaching from either direction (i.e., it is bidirectional).
Power Control
Published in Stephen W. Fardo, Dale R. Patrick, Electrical Power Systems Technology, 2020
Stephen W. Fardo, Dale R. Patrick
Limit switches are made in a variety of sizes. Limit switches are merely on/off switches that use a mechanical movement to cause a change in the operation of the electrical control circuit of a motor or other load device. The electrical current developed as a result of the mechanical movement is used to limit movement of the machine, or to make some change in its operational sequence. Limit switches are often used in sequencing, routing, sorting, or counting operations in industry. Ordinarily, they are used in conjunction with hydraulic or pneumatic controls, electrical relays, or other motor-operated machinery, such as drill presses, lathes, or conveyor systems.
Lifetime assessment of structural adhesive joints by combining effects of mechanical load, humidity, moisture and UV: design of a test rig
Published in The Journal of Adhesion, 2020
S. Fevery, H. Hallez, D. Vandepitte, S. Debruyne
The test device is built on a frame that nicely fits a climate chamber (ClimeEvent C/340/40/3) Two actuators are mounted on this frame, with the possibility of customizing the alignment and individual position. In this way, horizontal tests can be carried out inside the climate chamber. A PLC extended with a Sinamics S120[23] and Siwarex[24] module for each actuator ensures, respectively, the control and load measuring. As the actuators are mounted completely outside the test environment, the set-up is quite large and has an overall length if 4 m, a width of 1.8 m and a height of 2 m. Each actuator can reach a maximum load of 22.5kN and have a stroke of 300 mm. Limit switches are installed on the actuator to prevent damage to the load cells and actuators in case of collision, and to allow easy and quick homing. By calculating the distance between the two actuators the software program (PLC) decides if a certain movement can be carried out without a risk of collision. The position and movement of the actuators is measured with an encoder on the motor and due to the reduction box, the horizontal displacement resolution is smaller than 1 µm. Each actuator is equipped with an S-type load cell to provide the necessary information for quantitative evaluation of the specimen’s mechanical behaviour.