It provides differential output, or complementary signals, for better noise immunity, especially at higher voltages. The first output type is differential line driver, which will have two connections for each channel (Figure 4).
#TOTEM POLE OUTPUT VS OPEN COLLECTOR ON ENCODER DRIVER#
When you’re designing a system, you can choose from differential line driver (HV), push-pull (PP), and open-collector (OC) and pull-up (PU) output types. The higher accuracy commutation outputs will allow the motor to run more efficiently.Īfter selecting the correct number of channels for an encoder, the next task is selecting the electrical output type of the encoder channels. The typical encoder commutation accuracy is ☑º mechanical. Encoder commutation for DC motors is more accurate and repeatable than using Hall Effect sensors. The pole count of the encoder commutation tracks needs to match the motor pole count.
Encoder commutation channels can replace Hall Effect sensors in a brushless DC motor for motor control and timing. Some rotary incremental encoders have additional auxiliary channels for motor commutation. The index is normally 180º electrical and gated to either channel A or channel B.įigure 3: Quadrature encoder with an index channel Every time the index is triggered, the receiving device knows where the encoder is within its rotation. One common function of the index is as a home position locator. The index is also sometimes called a reference, marker or homing pulse. The index or “Z” channel of an encoder happens once per revolution of the encoder. This can increase the effective system resolution by up to four times. Many receiving devices also have the capability of using a quadrature encoder’s signals to perform edge counting to increase the resolution two or four times, sometimes called quadrature counting. This quadrature relationship provides directional information to the receiving device. Each channel of the quadrature encoder will have the same number of pulses per revolution offset by 90º electrical.
To make this determination, it is very important to understand the requirements of the receiving device.įigure 2: Quadrature encoder and quadrature countingĪ quadrature encoder has two channels, typically referred to as channel A and channel B. The second is the electrical output characteristics of the encoder channels.
The first is the number of output channels. There are two important considerations when selecting the outputs of an encoder. Incremental encoders will output a count or pulse at periodic predetermined intervals. Absolute encoders have a unique digitally coded output, or address, for every distinct position of the encoder. The thing to remember is that it’s the receiving device that determines the correct configuration of the encoder’s outputsWithin linear or rotary encoders, there are two basic types of electrical output formats: Incremental or absolute. However, this is one of the most common problems customers have when selecting encoders. Choosing the correct number of channels and the correct output type for an encoder can be the determining factor in whether or not a feedback system will function properly.
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