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A square wave describes one of the output choices of an encoder. If viewed on an oscilloscope, the square wave looks like this: it represents the on/off conditions of the sensing circuit. An “ON” condition is sometimes described as “HIGH” and an “OFF” condition is described as “LOW”. One entire pulse, 360°, equals 180° of an “ON” condition and 180° of an “OFF” condition. When the “ON” and “OFF” conditions are exactly 180° of the entire waveform, this is called a 50/50 duty cycle. The duty cycle can sometimes vary, and will be expressed as 50, ±X%, with “X” being the amount of variation that one could expect.

A “two-phase” encoder provides a second signal to the system it is feeding that allows the direction of rotation to be determined. This is done by offsetting one signal from the other by 90°. One signal is usually referred to as Phase A the other is Phase B. In one direction, Phase A will lead by 90° and in the other Phase B will lead. This is often called quadrature or A Quad B. This scheme is typically used with: regenerative drives, reversing drives, position controls and length measurements.

Direction sensing refers to the ability of an instrument or controller to determine the direction of rotation of a shaft/motor by looking at the pulses coming from the encoder. The encoder output must be a two-phase type quadrature with one phase 90° out of phase with the other.

• That is very much dependent upon the application.
• When interfacing an encoder to a drive for speed feedback, the drive manufacturer will typically specify an optimal PPR, or a maximum frequency by maximum motor speed in revolutions per second.
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• How to calculate pulses per revolution rate for a given frequency input limit and maximum motor or shaft RPM:
• RPM / 60 = RPS (revolutions per second)
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• Example A:
  Max. frequency: 10,000 Hz. Max. motor speed: 1700 RPM / 60 = 28 RPS
  10,000 Hz / 28 RPS = 357 PPR nearest standard PPR to be used is 360 for this example.

• How to calculate frequency output of an encoder given the PPR and maximum motor or shaft RP:
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• Example B:
  Max. motor speed is 3600 RPM / 60 = 60 RPS. Encoder PPR is 1024
  Max. frequency output of encoder at 3600 RPM. 60 RPS x 1024 PPR = 61,444 Hz.

• In Example A, a 360 PPR encoder would work perfectly. If the desired PPR is not listed among the standard/stock items, then select the next lower value, or contact encoderhelpdesk@nidec-industrial.com.
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• When selecting an encoder for positioning accuracy, calculate the needed resolution by converting the physical accuracy required of the load (say 0.001″) to the amount of rotation seen by the encoder (through the gearbox, if any) (example: 1°). Calculate the minimum PPR = 360 / (movement in degrees) x 2 = 720 PPR. Ideal PPR = minimum x 5 = 3600 PPR.
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• Select an encoder between minimum and ideal values, keeping in mind any possible frequency limitations on the input device (see Example A). The default PPR for most new applications worldwide is 1024 PPR – high enough to give accuracy, but low enough not to overflow most recent drives and controls with too many pulses per second. 1024 PPR encoders are in-stock by most manufacturers and distributors worldwide, which makes them an easy choice.

Short circuit protection is an important feature in any encoder, especially in a multi-sectional drive control system where downtime can cost thousands of dollars per hour.

Short circuits can occur for a variety of reasons, including varying errors and cable faults. With certain types of line drivers, this can cause a complete failure of the encoder and necessitate removal and replacement. With a protected circuit, the encoder may not function if miswired, but it can be rewired and operated without replacing the encoder itself. Many Avtron Encoders come with protection circuitry.

Encoders come with a variety of outputs to suit many different applications. Variables that determine what will work best include output frequency, cable type, cable length and drive input circuits. Some line drivers offer high power for long wires, but sacrifice short circuit protection. Others are fully protected, but cannot drive long wires, particularly at higher voltages. Nidec’s latest high power line drivers are both powerful and short circuit protected. These drivers are available on THIN-LINE III™ (AV56, AV56S, AV67, AV85, AV115), SMARTach III™ (AV125, AV485, AV685, AV850), as well as the HS35M. Consult the system manufacturer to determine input requirements and then consult the encoder specification guide for your selection. You may also contact our Encoder Help Desk for assistance. Some models of line drivers on older SMARTach™ models (M285, M485, M685, M1250) also greatly affect current draw of the encoder, so check the manual before specifying a particular driver.

A complementary signal is the inverse of a standard encoder output signal. When Phase A is high, the complement of Phase A, called Phase “A NOT” is low. When Phase A is low, Phase A NOT is high. Complementary signals are sometimes called “differential” because of their use with differential amplifiers. Differential amplifiers accept both the Phase A, Phase A NOT, and Phase B, Phase B NOT signals and are usually used where long cable runs exist and high noise immunity is needed. These are also known as quadrature or A Quad B signals.

Open collector outputs are an older system using a single output transistor to bring the output to zero volts, then a “pull-up” resistor wired to V+ to bring the voltage to the high level. They produce square waves like modern line driver outputs, as long as the cable is not too long. Open collector outputs can be replaced by modern line driver outputs; be sure to remove any external or internal pull-up resistors remaining in the circuit.