BANNER BES58-6 series incremental encoder selection and troubleshooting guide

BANNER BES58-6 series incremental encoder selection and on-site troubleshooting complete guide

In the field of industrial automation, rotary encoders are the core feedback components for measuring angles, positions, and speeds. The reliability of the encoder directly determines the operational quality of the entire system, from the speed control of the servo motor to the position limitation of the crane. However, facing the dazzling array of encoder models on the market (NPN, push-pull, line drive HTL、TTL……）， As well as common faults such as signal loss, counting errors, and mechanical damage on site, many maintenance engineers are confused. This article will take a typical industrial incremental encoder (referring to the 6N/6H/6T/72T series) as an example to provide you with a full process practical guide from selection, installation to fault diagnosis.

‍

Incremental Encoder Core Selection: Output Type and Electrical Matching

Choosing the wrong output type of encoder is one of the most common errors on site. Different controllers and counters require different signal interfaces. Let's analyze the four mainstream output methods one by one.

1. NPN open collector output (model suffix 6N)

Electrical characteristics: The emitter of the output transistor is grounded and the collector is open circuit. An external pull-up resistor is required to obtain a high-level signal.

Applicable scenarios: Early Japanese PLCs or counters, with a common anode input circuit (receiving low level valid). The power supply voltage range is wide (10-30VDC), the maximum driving current per channel is 30mA, the maximum output frequency is 100kHz, and the rise time is about 1 microsecond.

Fault tendency: If the pull-up resistor is not installed correctly, the signal will always be at a low level, causing abnormal counting. In addition, the anti-interference ability is weak during long-distance transmission.

2. Push Pull output (model suffix 6H)

Electrical features: It contains a pair of complementary transistors that can output both high and low levels without the need for external pull-up resistors.

Applicable scenarios: Compatible with most controllers with NPN and PNP inputs, it is an ideal choice for universal replacement. It also supports 10-30VDC power supply, with a frequency of 100kHz and a rise time of 1 microsecond.

Advantages: Strong signal driving capability, suitable for medium distance transmission (tens of meters). In the renovation of old equipment, if the output type of the original encoder is uncertain, push-pull output is usually a safe choice.

3. HTL output (High Threshold Logic, model suffix 6T)

Electrical characteristics: High threshold logic, usually output signal amplitude is the same as the supply voltage (10-30V), with stronger anti-interference ability. This model 6T provides 6 signals (A, A -, B, B -, Z -), namely differential output.

Applicable scenarios: applications with harsh industrial environments and long cable distances (up to 100 meters or more). Differential signals (A and A -) are transmitted through twisted pair cables, and common mode interference can be effectively suppressed.

Parameters: Power supply 10-30VDC, maximum no-load current of 150mA (higher than the previous two, please pay attention to power capacity), rise time of only 100 nanoseconds, much faster than NPN/push-pull.

4. TTL output (Transistor Transformer Logic, model suffix 72T)

Electrical features: Fixed 5V power supply, differential output (RS-422 compatible). The signal amplitude is usually 5V and the rise time is 100 nanoseconds.

Applicable scenarios: Connecting high-speed counters, servo drives, or motion control cards. Due to low voltage, it is not suitable for long-distance transmission (recommended to be less than 10 meters). Six signal lines (A, A -, B -, Z -) provide extremely high noise resistance performance.

Attention: Never connect 24V power supply, otherwise the output stage will be immediately burned out.

On site selection checklist

Recommended input type for controller, maximum distance for encoder output power supply

Common anode (low level effective) NPN (6N) 10-30V<30m

Common cathode (high level effective) or unknown push-pull (6H) 10-30V<50m

HTL differential (6T) 10-30V 100m for long-distance and strong interference scenarios+

5V TTL differential interface TTL differential (72T) 5V<10m

Mechanical specifications and installation points: Avoid physical damage

The mechanical lifespan and reliability of encoders largely depend on whether they are installed correctly. According to the provided mechanical specification table:

Speed limit: Maximum 6000 revolutions per minute. Exceeding this speed may cause the bearing to overheat or the photoelectric encoder to shatter.

Axle load: maximum axial load of 40N, maximum radial load of 20N. This means that it is not allowed to use hammering to install the coupling, nor is it allowed for the pulley to be too tight. Excessive radial load is the primary cause of premature damage to encoder bearings.

Starting torque: 5 × 10 ⁻⁷ N · m, very small, only needs to overcome bearing friction and sealing resistance. This implies that the encoder cannot be rigidly connected to the motor shaft and a flexible coupling must be used.

Protection level: IP65. Can prevent dust and water spray, but not suitable for immersion. If there is oil mist or cutting fluid splashing on site, additional protective covers should be added.

Vibration and impact: Anti vibration of 100 m/s ² (10-200Hz), anti impact of 1000 m/s ² (6ms). If there is severe vibration in the equipment (such as a crusher), it is recommended to use a buffer installation bracket.

Installation steps and common errors

Axis alignment: The coaxiality deviation between the encoder shaft and the motor shaft should be less than 0.1mm, and the angle deviation should be less than 0.5 °. Excessive deviation can lead to seal ring wear and bearing abnormal noise.

Coupling selection: Special elastic couplings (spiral or diaphragm) must be used, and rigid connections are absolutely prohibited.

Cable fixation: The encoder tail cable should have a stress relief ring at the outlet. Cables should not withstand tension or repeated bending, otherwise the internal wires will break.

Avoid knocking: It is strictly prohibited to knock the encoder housing or shaft during installation, otherwise it may damage the internal precision encoder disc.

Signal output waveform and phase analysis: decoding channels A, B, and Z

The core output of an incremental encoder consists of two orthogonal square wave signals (A and B) and one zero position signal (Z). A correct understanding of these waveforms is a prerequisite for diagnosing signal problems.

Based on the waveform provided in the document, we have summarized the key parameters as follows:

Phase difference: The electrical angle phase difference between phase A and phase B is 90 ° (T/4). When the shaft rotates clockwise (as viewed from the extended end), phase A leads phase B by 90 °; If rotated counterclockwise, phase B leads phase A. The counter determines direction by detecting this phase difference.

Duty cycle: The high-level and low-level times of each signal should each be close to T/2. The allowable deviation given in the waveform diagram is: X ₁+X ₂=0.5T ± 0.1T, X ₂+X ∝=0.5T ± 0.1T. If the duty cycle deviates significantly, it may be due to dirt on the encoder or aging of the optoelectronic components.

Zero position signal width: The Z signal appears once per revolution, and its width TM=0.25T ± 0.1T (when the number of pulses per revolution is less than 2000); When the number of pulses is ≥ 2000, TM=0.5T ± 0.15T. The Z signal is used to determine the absolute zero point. If the Z signal is lost or the width is abnormal, it will cause inaccurate zeroing.

Using an oscilloscope to diagnose signal faults

Connect the oscilloscope probes to A, B, Z, and the common terminal (GND) respectively. After the power supply is normal, slowly rotate the axis and observe the waveform:

No signal: First check if the power supply (VCC and GND) is normal, and then check if the LED indicator light (if any) is on. If the power supply is normal but there is no output, it may be due to damage to the internal optoelectronic components.

A certain signal is always high or low: it may be due to the breakdown or open circuit of the output transistor of that channel. For open collector output, check the pull-up resistance.

Serious signal glitches: Common causes include ungrounded shielding layers or parallel wiring of cables and power lines. Twisted pair shielded cables should be used, and the shielding layer should be grounded at one end.

The phase difference is not 90 °: it is usually due to physical damage to the encoder or grating, and the encoder needs to be replaced.

Electrical Connection and Wiring Color Specification: Pin by Pin Diagram

The document provides a key wiring color chart, which is the only basis for on-site wiring. The pin definitions for different output models are different, and incorrect wiring may result in immediate damage.

6T (HTL differential) and 72T (TTL differential) wiring (6-wire differential)

Explanation of wire color signal

Positive pole of red VCC power supply (6T: 10-30V, 72T: 5V)

Black 0V power supply negative pole/public ground

Green A-phase positive signal

Powder A-A phase inverted signal

Yellow B phase positive signal

Blue B-B phase inverted signal

White Z zero position positive signal

Orange Z-Zero Inverted Signal

Screen (bare wire) GND (shield) connected to the ground on the controller side

6H (push-pull) and 6N (NPN) wiring (3 wires or less)

Note: Push pull and NPN typically only have three single ended signals: A, B, and Z (sometimes with reverse signals added, but not explicitly stated in the documentation). Simplified wiring color:

Red: VCC

Black: 0V

Green: A

Yellow: B

White: Z

Shielded wire: grounded for protection

Common wiring errors on site

Connecting the 5V encoder to a 24V power supply: caused the 72T to burn out. Be sure to verify the model suffix.

The differential signal is only connected to one wire: connect A+to the A terminal of the counter, with A - suspended. Differential receivers require both to recognize correctly, and suspension can lead to uncertain signal levels. Correct approach: A - should be connected to the A - terminal of the counter (or pulled down through a resistor).

Shielding layer incorrect grounding: Grounding both ends will generate ground current, introducing interference. The correct approach is to only connect the controller side to a single end ground.

Cable too long leads to voltage drop: For 5V TTL, the signal amplitude may drop below the receiving threshold after the cable exceeds 10 meters. You can use a line driven repeater or HTL encoder instead.

Practical troubleshooting: a complete repair case

Fault phenomenon: The X-axis position of a CNC machine occasionally jumps by+10mm and then returns to normal. The servo drive did not alarm, but the displayed actual position deviates too much from the commanded position.

Troubleshooting steps:

Observation of symptom characteristics: The position jump is sudden and irregular. This implies that it is not a mechanical clearance issue (which can lead to consistency hysteresis), but rather electrical noise or encoder pulse loss.

Check the mechanical coupling: manually rotate the screw after power failure, while observing whether the encoder shaft rotates synchronously. It was found that the fastening screws of the coupling were not loose, ruling out pure mechanical slippage.

Measurement of power supply voltage: Measure VCC and 0V at the encoder terminal. Rated 24V, actual measurement fluctuates between 23.5V and 24.5V, normal. But when observed with an oscilloscope, it was found that there was a high-frequency ripple with an amplitude of about 1V (from servo driver PWM feedback). Ripple may interfere with NPN output.

Analysis output type: The on-site encoder model is 6N (NPN open collector). NPN output is more sensitive to ripple because low-level signals may be misjudged as high-level under noise.

Capture A-phase waveform with oscilloscope: Set the oscilloscope to rising edge trigger and scan time to 10ms/div. When the machine tool is running normally, the waveform is a clear square wave. But when the fault occurred, an abnormal low-level spike was captured - a low level lasting about 20 microseconds, equivalent to losing several pulses.

Diagnostic root cause: Due to the need for a pull-up resistor for NPN output, the controller used on site is internally pull-up (2.2k Ω to 24V). Due to the length of the cable reaching 30 meters and the large distributed capacitance, coupled with power ripple, the rising edge of the signal becomes slower and more susceptible to interference. Push pull or HTL differential output has stronger driving capability.

Solution: Replace with a push-pull output encoder (6H). Reconnect the wires (no need to pull up), run again, the position jump disappears, and the oscilloscope displays sharp edges of waveforms A and B without burrs.

Preventive measures:

In long-distance or strong interference situations, HTL differential output (6T) is preferred.

The encoder cable should be routed in separate slots from the power line, with a minimum spacing of 20cm.

Install ferrite magnetic rings or power filters at the input end of the encoder power supply.

Environmental factors and maintenance cycle

According to environmental specifications, the working temperature of the encoder is -10 ℃~+70 ℃, and the storage temperature is -20 ℃~+80 ℃. In high temperature, high humidity, or dusty environments, additional measures should be taken:

High temperature: If the equipment is close to an oven or engine, the environment may exceed 70 ℃. In this case, a high-temperature resistant encoder or thermal isolation should be selected.

Oil pollution: IP65 can resist slight oil mist, but if oil is directly sprayed (such as gearbox leakage), the oil may seep into the interior along the shaft seal, causing contamination of the encoder. Regularly check whether there is oil accumulation at the shaft seal.

Vibration: Long term vibration can cause internal welding points to loosen or code discs to shatter. It is recommended to conduct signal waveform testing every 6 months to check for any abnormal jitter.

Suggested maintenance plan

Monthly: Check if the cable skin is worn and if the connectors are securely fastened.

Quarterly: Manually rotate the shaft and check for any jamming or abnormal noise (signs of bearing wear).

Every year: Use an oscilloscope to record the A, B, and Z waveform benchmarks, compare them with the initial waveform, and identify early degradation trends.