Quadrature encoders are commonly used as the sensing elements in machine tools and other applications which require high-accuracy measurement of position, speed or angle. Applications include industrial controls, robotics, optical systems, metrology instruments, rotating radar platforms, and more. The typical quadrature encoder consists of a scale with light and dark elements, which are sensed by two optical detectors. The A and B outputs of these two detectors, called quadrature signals, are 90° out of phase. Their up and down phase changes can then be counted, and their phase relationship determines the up (+) or down (-) count direction. A zero index signal, or Z signal, may be added as a third input to the A and B signals to provide a home position.
Using a quadrature meter with a digital encoder:
A quadrature meter by Laurel Electronics accepts the A and B quadrature signals from linear encoders and shaft encoders to provide a highly accurate, scaled display of position, rate, or angle in engineering units, such as ft, cm/sec, or degrees. The panel-mountable meter provides a six-digit LED display, which can be scaled by the user for the appropriate units of measure, not just raw quadrature encoder counts.
Application examples of quadrature meter:
X-Y position or rate can be obtained from two shaft encoders, which convert linear position to quadrature signals as two shafts turn. In addition to serving as a display, each quadrature meter can use its optional dual or quad relay setpoint capability for closed loop control. It can also transmit data to a computer or a PLC via the Ethernet, USB, RS232 or RS485 serial communications, or via a 4-20 mA analog signal.
Controlling the repetitive cutting of material to length, such as sheet metal, is an excellent application of a quadrature meter. The quadrature encoder shares the shaft of a sensing wheel, whose rotation corresponds to lineal displacement of material. The meter compares the displacement reading against setpoint information, and then uses its dual relays to first slow down and then cut the material.
Quadrature has been used to track position and vertical drilling speed of the bit in an oil drilling operation. A shaft encoder is rotated by a cable that moves with the drilling shaft. In this application, the same encoder signal is applied to a Laurel quadrature meter for position, and to a second quadrature meter for rate. Both meters can be scaled to read out in appropriate engineering units, such as feet and inches per minute, and can be alarmed. A Laurel 6-digit remote display could have been added to read out peak rate.
Features to look for in a quadrature meter:
Look for a display that has at least six digits, since encoder provide high resolution. Look for scalability, so that the reading can be in appropriate engineering units, such as mm, inches, meter for position, or in mm/sec, inches/sec, etc. for speed. Also look for programmability to measure and add offsets, and to count up to a preset or to count down to zero. The objective of most digital encoder measurements is control, so ensure that your meter offers at least two relays, ideally four relays. For example, two relays can be determine the low and high ends of travel, while two additional relays server as prewarns to slow down travel as the system approaches these two limits.
Also think of the future, where most instruments will be networked. Look for options that will allow your encoder meter to work as part of a larger system and to be interfaced via an Ethernet network. A state-of-the-art counter should offer a choice of plug-in boards for communications, control, and network use. For example, serial interface boards by Laurel Electronics include Ethernet, USB, RS485 and RS232. Additional boards can provide a 16-bit, isolated analog output, and dual or quad relays for alarm or control. Look for other features that you may need, such as a red or green LED display, and large digit heights. Laurel offers digits up to 8” high for a viewing distance up to 300 feet, for example across a factory floor.
Contact Laurel Electronics for a quadrature meter to meet your needs