May 21, 2021 Encoder
Encoder is a device that is used in many industries to provide feedback. An encoder senses position, direction, speed or count and feedback to the system. Encoder convert motions to an electrical signal that can are sent to some sort of controlling device such as PLC and is interpreted to represent a value that will be used within the program. Encoders use different types of technologies to create signal, including: mechanical, magnetic, resistive and optical. For example, in optical sensing, the encoder provides feedback based on the interruption of light. A beam of light is pass through a disk that has opaque lines in a specific pattern, where there is another light detector on the other side that will interpret the light based on the pattern on the disk. The pulses of light are then converted to an electrical signal and sent to the processor
Encoder have many uses which include close-loop applications of encoder such as servo or VFD control, measuring and counts. For example, when using the encoder on VFD control to fill a tank with a certain speed, the encoder on VFD may be used for feedback of actual speed of the pump.
Encoder has many types but all falls into two category of sensing technique, linear and rotary. Within those categories, there are differing encoder measurement types such as absolute and incremental.
Linear encoder uses transducer to measure the distance between two point. These encoders can use a rod or a cable that is run between the encoder transducer and the object that will be measure for movement. As object moves, the transducer’s data collected from the rod or cable created an output signal that is linear to the object’s movement. The position of the object is able to be identified by using this information.
Rotary encoder collects data and provide feedback based on the rotation of an object. Rotary encoder is also called shaft encoder. These encoder uses can convert object’s angular position or motion based on the rotation of the shaft, depending on the measurement type used.
Linear encoder can measure distance, speed and linear position, whereas rotary encoder can only measure angular position. Absolute encoders and incremental encoders both measure the angle position based on the position of the shaft. Within an absolute encoder, this position retained regardless of whether the encoder is powered on or not, even if a movement is made without power to encoder and power is reapplied, the encoder knows it true new position.
Taking rotary “absolute” encoder, a slotted disc on a shaft is used in conjunction with a stationary pickup device. When a shaft rotates, a unique code pattern is produced. This means that each position of the shaft has a pattern and this pattern is used to determine the exact position. The encoder will always able to record the absolute position as demonstrated by the unique pattern transmitted by the disc and received by the pickup.
Absolute encoder is preferred in applications requiring a great degree of certainty such as when safety is primary concern. Because the encoder knows, at all times, its definitive position based on the unique pattern produced. Absolute measurement encoders can be single-turn and multi-turn where single-turn encoder are used for measurements of short distance while multi-turn would be more suitable for longer distances and more complex positioning requirements.
For incremental measure encoders, the output signal is created each time that the shaft rotates a measured amount. The output signal is then interpreted based on the number of signals per revolution. The incremental encoder begins its count zero when powered on. Unlike absolute encoders, there are no safeguards regarding the position. Because the incremental encoder begins its count at zero in start-up or power disruption, it is necessary to determine a reference point for all tasks requiring positioning.
An example of the application of incremental encoder is the application of the incremental encoder on a conveyor belt. The count the incremental encoder received is in the range of 0 to 10000. Where the absolute position is not known, but the full revolution of the shaft registers a count of 10000. Let’s say an object go through a photo-eye sensor and it able to detect it and the current encoder count is 5020.
The object is once again captured by the photo-eye sensor located at the exit when the encoder count is at 6311. So, by the numbers obtained, we can conclude that the travel is 1291 counts. Thus, the travel count of from the entrance to the exit is 1291 counts, even though it does not tell us at what position the object currently is but we know that the object will enter at any number and exit at the number plus 1291 counts.
Encoder are available through Quick Time Engineering Inc.
Quick Time Engineering Inc is an international company with offices and distribution networks in the USA, Hong Kong, Europe and Malaysia.
In its 20 years of operation since 1998, Quick Time Engineering Inc had emerged from a local engineering company with a single staff that provided solutions in factory automation to become nowadays a company that serves the Oil & Gas industries, EPC contractors, System Integrators and other industrial automation and process control companies worldwide. Customers from over 50 countries worldwide trust us with their need for process control instruments and industrial automation products.
For more information about Quick Time Engineering Inc, visit www.quicktimeonline.com or email enquiry@quicktimeonline.com
