What is an encoder ?
An encoder is a device that converts angular or linear displacement into electrical signals. The former is called a code disk, and the latter a code scale. According to the reading method, encoders can be divided into two types: contact and non-contact. Contact encoders use brushes for output, with the brushes contacting conductive or insulating areas to indicate whether the code state is "1" or "0". Non-contact encoders use photosensitive or magnetic sensitive elements for receiving signals. When using photosensitive elements, the light-transmitting and opaque areas are used to indicate whether the code state is "1" or "0".
Encoders can be classified into two categories based on their working principle: incremental and absolute. Incremental encoders convert displacement into periodic electrical signals, then convert these signals into counting pulses, using the number of pulses to represent the magnitude of the displacement. Absolute encoders, on the other hand, assign a unique digital code to each position; therefore, their reading depends only on the starting and ending positions of the measurement, and is independent of the intermediate steps.
What is the definition of measurement accuracy?
As we all know, all measurements are approximate estimates of the "true" value. In other words, the measured value always has a certain error compared to the "true" value. The magnitude of such error is what is commonly referred to as measurement accuracy, which reflects the ability of the measuring instrument system to accurately reproduce the measured signal value.
What is the accuracy of the incremental encoder?
The accuracy of an incremental photoelectric encoder is completely unrelated to its resolution; these are two different concepts. Accuracy is a measure of the ability to determine the position of any pulse relative to another pulse within a selected resolution range. Accuracy is usually expressed in angles, arcminutes, or arcseconds. The accuracy of an encoder is related to the manufacturing quality of the light-transmitting slits in the code disk, the mechanical rotation of the code disk, and the installation technique.
What is the resolution of the incremental encoder?
The resolution of a photoelectric encoder is expressed as the number of basic cycles of the output signal produced by one revolution of the encoder shaft, i.e., pulses per revolution (PPR). The number of light-transmitting slits on the code disk equals the encoder's resolution; the more slits engraved on the code disk, the higher the encoder's resolution. In industrial electrical drives, depending on the application, incremental photoelectric encoders with resolutions typically ranging from 500 to 6000 PPR can be selected, with some reaching tens of thousands of PPR. Encoders with a resolution of 2500 PPR are commonly used in AC servo motor control systems. Furthermore, logical processing of the photoelectric conversion signal can produce pulse signals at 2x or 4x frequency, thereby further improving the resolution.
What is the relationship between the accuracy and resolution of an absolute encoder?
The number of bits in a single-turn absolute encoder represents the number of code tracks on the code disk. Because it uses a binary code disk (the same as Gray code), its precision becomes a power of 2. For example, 12 bits is 2 to the power of 12, which is 4096.
Encoder resolution and accuracy are not necessarily equivalent. Accuracy is determined by various factors such as the groove markings, the mechanical concentricity of the code disk, the reading response speed, and temperature characteristics. If an encoder achieves high resolution by using sine wave subdivision for the groove markings, its accuracy is not improved; subdivision only increases the resolution. The accuracy of the groove markings before subdivision is the same as the accuracy after subdivision. Therefore, the accuracy of some high-resolution encoders depends on the number of lines used for subdivision in the first step.
II. Hengstler Brand
How is the maximum frequency of data polling determined through the SSI interface?
The following "best case" and "worst case" scenarios must be considered when using the current location data transmitted via SSI.
The output of location data depends on several parameters, such as the factor, conversion time, and data format. Therefore, the processing time will vary.
Using a processor system, you will "only" get an average response time. If you poll the SSI channel at a maximum frequency of 500kHz, that is (pulse time 2µs * 26 bits + minimum required pause time 40 microseconds), the shortest time is approximately 100µs. After that, the system will need another 400-500µs for data updates, so in the "worst case," you might get the same result (position value) three times! Only by using a much faster DSP or ASIC can you get shorter times (by a factor of 10), or by using an encoder with a built-in SIN/COSINE code track for motor control systems.
What are the differences between AC59 and AC61?
Both encoder models feature stainless steel housings. The "61" model has a solid, robust stainless steel housing connected to a stainless steel flange. Standard cable fittings are made of nickel-plated brass. This design allows for complex encoder types, such as absolute encoders with bus covers and those requiring protected access to the encoder's internals, such as DIP switches. The "59" model includes a drawn stainless steel housing connected to a crimped stainless steel flange. Standard cable fittings are made of PVC. This design is generally less expensive (offering encoder types with reduced requirements): incremental encoders with cable connectors, absolute encoders with cable connectors, and sealed housings (such as parallel single-turn, SSI, or BiSS).
What are the differences between solid shaft encoders and hollow shaft encoders?
Solid shaft encoders require mounting flanges and couplings. Hollow shaft encoders only require a single spring plate to prevent encoder rotation and absorb vibration.
What GSD file do you need to use when using the ACURO encoder?
You can use the same GSD files as the ACURO AC58 series encoders. The reason is that if the RA58 fails, the user will replace it with an AC58. If the encoder codes are different, the PLC (which uses the GSD file for recognition) will not be able to connect to the AC58 encoder replacing the RA58, so the PLC software must be modified. Making them the same makes it easier for users to apply the technology.
III. Dynapar Brand
What is Differential Line Driver Output?
Differential outputs refer to the fact that each channel has a complementary channel, such as A and /A. Differential line drivers can help improve noise immunity (see What are the /A and /B channels used for?). Differential line drivers also allow for more drain or source current than push-pull outputs. Differential line drivers have both drain and source circuitry working simultaneously. (See What is a drain or source input?) It can also help increase signal propagation distance.
What is Open Collector Output?
An open-collector output is an NPN transistor. An NPN transistor allows leakage current to the common terminal. It can be thought of as a switch, allowing the circuit to be connected to the common terminal after a load has passed through it. This means that a power supply is required for the output to operate. The power supply must be connected to the output after a load has passed through it; otherwise, the NPN transistor simply establishes a path to the common terminal, i.e., a dry contact. Therefore, if you measure the voltage of an open-collector output that is not connected to any power supply, you will not see a change in voltage. If the open-collector is operating normally, the voltage should be detectable after a load has passed through the output.
What is Totem Pole Output?
Totem-pole output is essentially the same as push-pull output, but it's a commonly used term when referring to TTL devices. The main difference between them is the magnitude of the drain or source current. Totem-pole outputs have lower drain/source current than push-pull outputs. Other key differences lie in the output voltage. Totem-pole outputs accept only a 5V DC signal, while push-pull outputs follow the input voltage.
What is push-pull output?
A push-pull output is an output that allows you to connect either a drain or source circuit simultaneously. (See What is a drain or source input?) This type of output allows you to draw more current and follow the input voltage than a totem-pole output. A push-pull output is necessary when the controller with an open-collector output and encoder connection is not functioning.
What is quadrature output?
Quadrature output means there is a 90-degree phase shift between signals A and B, with A leading B or B leading A depending on the direction of rotation. This does not mean the output will have four times the encoder's resolution per revolution. The fact that the signals have a 90-degree phase difference allows the controller to determine the encoder's rotation direction. You must use quadrature signals A and B simultaneously to obtain X2 or X4 logic relationships. (See What's the difference between quadrature and X4 logic?)
Why do I need a pull-up resistor?
Pull-up resistors are used to "pull" logic high voltage levels to the operating voltage. This is very useful when the open-collector output does not reach the voltage level required to display a logic high level or when noise appears on the signal line. When a logic high signal occurs, the voltage level for an open-collector circuit is approximately equal to the operating voltage. The difference is due to the voltage drop across the pull-up resistor. This is not necessary if the load is not ground-referenced.
What are the uses of channels A and B?
The /A and /B channels are the inverse signals of the /A and /B channels. This means that when signal A is high, signal /A is low, and when A is low, /A is high. This also applies to any situation with complementary signals. This typically minimizes noise. Some input cards accept both the A and /A signals simultaneously. The two signals are then compared to help eliminate common-mode noise that may have infiltrated the conductors. A received pulse is only acknowledged when signal A is high and signal /A is low. This applies to any channel with complementary signals ; signal A is just one example. This is often referred to as differential output.
What are the differences between orthogonal and x4 logic?
Quadrature output refers to the phase shift of the output signals. When the output signals, A and B, are 90 degrees out of phase, this is called quadrature. This is just an explanation of the term "quadrature." (See What is Quadrature Output?)
The x4 logic refers to how the controller interprets the received signals. This is done by converting the edges of each detected A and B channel pulse into its own pulse. This conversion occurs in the controller, not the encoder.
This means that if you order a quadrature encoder with 120 pulses per revolution, the output signals A and B will have a 90-degree phase shift. This does not mean the encoder will generate 480 pulses per revolution. The additional pulses only occur in the controller.
How do I select the pulses per revolution (PPR)?
When selecting the PPR value for your encoder, keep some simple rules in mind. Ensure that the PPR value you choose does not exceed the maximum frequency of your controller or encoder. Try to choose a PPR close to the value you want to display, thus eliminating or reducing the need for a calibration constant. For example, if you want to display 12 inches per revolution, choose a PPR of 12. If you want to display 12.00 inches, choose 1200 PPR. However, don't forget the multiplier of your controller input. Most controllers have either X2 or X4 logic. With X2 logic, displaying 12.00 will result in a PPR of 600; with X4 logic, it becomes a PPR of 300. These choices give you only one pulse per unit as you expect. Remember to keep the frequency in mind when you create your PPR. When selecting a PPR, do not exceed the frequency that the encoder can handle at the highest speed. Conversely, do not choose a PPR that is too low, as your controller will not be able to recognize the signal. Try selecting your PPR so that your calibration constant is between 0.5 and 1.
How do I set my calibration constant?
Choosing the correct pulses per revolution (PPR) can simplify the calibration factor selection. Once the PPR is selected, you can either simply calculate it according to the formula in the technical manual. When choosing the calibration constant, remember that the closer to 1, the better. The value of the calibration constant is the resolution per pulse of your best encoder.
How far apart can the Dynapar encoder be from my system?
There is no fixed answer. Many factors come into play, including the maximum cable length connecting the devices together. The biggest problem with using long cables is that they become more susceptible to noise interference. This is due to the cable's capacitance, which causes it to act like an antenna, and there are power losses through the cable. The maximum cable distance can be determined, but some basic wiring principles must be followed: Keep cables away from objects that generate significant electrical noise. This includes AC motors, arc welding machines, AC power lines, and transformers. Use twisted-pair cables when using complementary signals, and shielded cables when using any type of signal. Use the highest permissible output voltage. For example, if the encoder can output 5 to 24 volts, use 24 volts. Use open-collector or differential line driver outputs with a differential receiver (PM28S00) to obtain the maximum drain/source current source.
If you are using an encoder as an input to more than one controller, use a signal amplifier. This is also a good way to increase the signal transmission distance. When using differential inputs, the typical maximum distance for a differential line driver is about 100 feet, and for an open collector, it is about 35 feet.
What is a zero-speed sensor?
The zero-speed indicator is a separate output that triggers an alarm when the speed falls below a certain frequency, not when the speed is actually zero. Zero speed itself cannot be detected; only a drop below a certain frequency can be detected. This is extremely useful when the application is critical and requires constant monitoring.
Do we need to use shielded cables?
Yes. Shielded cables are highly recommended, especially in areas with significant electrical noise. If you have any noise problems, or suspect there might be, please use shielded cables.
Why use an absolute encoder?
First, what is an absolute encoder? An absolute encoder has a unique code for each position per revolution. Instead of pulse output, you obtain a binary value output. This is extremely useful when accurate position is required. Because an absolute encoder has a unique binary value for each position per revolution, the actual position can be identified even if the power is off and when power is restored. This applies even if the controller loses power and the process is moved.
What is Gray code?
Gray code is a form of binary code. The difference between Gray code and binary code lies in the method of increment. In Gray code, only one bit changes with each increment. This means the counting order will be 0 , 1 , 3 , 2 , 6, and 7. This differs from standard binary, which uses the order 0 , 1 , 2 , 3 , 4, and 5.
Gray code binary
0000000000
0001100011
0011200102
0010300113
Gray code prevents errors that occur during transitions to the next state. Here's an example illustrating what might happen. This could be due to timer and cable capacitance. A transition from 0011 to 0100 might result in 0111, a possibility that Gray code would not present.
How do I convert Gray code to binary code?
The following is an example of converting Gray code to binary code.
Step 1
Write the number down and retain the highest bit of the Gray code as the highest bit of the natural binary code. (11011 Gray code = 1 binary)
Step 2
The second-highest natural binary code is obtained by XORing the highest natural binary code with the second-highest Gray code. The XOR operation returns 0 if the bits are the same, and 1 if they are different. (11011 Gray code = 10 binary)
Step 3
Repeat step 2 until all numbers have been converted.
11011 Gray code
100 binary
11011 Gray code
1001 binary
11011 Gray code
10010 binary
What is a leaky or source input?
Drain and source inputs only involve the flow of transistor current. This means they require both voltage and load to operate. A drain input requires both voltage and load before it is connected to the circuit. For the circuit, this is "draining" to ground. A source input must be placed before the circuit's load. This means it is "source" current to the circuit. Both voltage and load must be present in either case to detect changes in the input voltage. The same applies to drain or source outputs.
What are the main differences between the outputs of the line drivers 7272 and 4469?
Linedrives
As the name suggests, this type of output chip originates from "driving" current to the line. Unlike open-collector outputs, line driver chips actively drive the output high or low, thus enabling the load to generate drain and source currents (see Figure 2). The main advantage is its line-driving capability, allowing it to push higher currents through the cable and enabling longer cable runs. While line drivers can be used in single-ended formats (i.e., push-pull outputs), they are most commonly used for complementary or differential signals. When using differential signals, line drivers are preferred when using shielded twisted-pair cables, operating with longer cables, or in high-noise environments.
7272
The 7272 is perhaps one of the most widely accepted line drivers. This chip is used in many competitive encoders for good reason; the 7272 achieves a good trade-off between current capability, usable voltage range, and chip cost. Typical current output capability for the 7272 chip is in the 40-50mA range, suitable for cables running in proximity to the encoder at 50-75 feet. Furthermore, the 7272 chip generally offers a “mirror voltage” output, meaning that regardless of the input encoder voltage, the output voltage will be the same (minus a small amount to account for the encoder’s power requirements). Another significant feature is its temperature protection function. If the 7272 is driven to its limits (high load, high voltage limits, high frequency) and the temperature rises, it enters protection mode, initiating an “exit” or stopping the output. If allowed to cool, the chip will restart, much like a thermal switch, and begin operation again. However, too much of this can cause the reset threshold or start-up point to decrease over time, eventually leading to encoder unreliability. In short, if the application continuously causes such shutdowns, a different line driver should be selected.
4469
The 4469 is another very prominent line driver option. Unlike the 7272, the 4469 has a much higher current drive capability, typically in the 100mA range depending on the manufacturer. This is a significant advantage for applications with longer cable runs, typically 100-300 feet. However, this higher current capability comes with a drawback. The 4469 wastes so much energy that its high current voltage range is affected. A typical mirrored voltage output is limited to 15VDC, although the input voltage can be increased to 24V if an adjustable 5V output is selected. In terms of cost, the 4469 is comparable to the 7272. Furthermore, the 4469 lacks automatic protection features; it can drive at full power without worrying about downtime, but this has a significant negative impact on its lifespan.
IV. NorthStar Brand
Can the NorthStar encoder provide 26V output?
Yes, we have designed a new generation of sensors that are compatible with all our RIMTach® and SLIMTach® products.
Can NorthStar sensors provide orthogonal, bidirectional, or Z-signal outputs?
Yes, all our sensors are capable of providing velocity and direction feedback signals (orthogonal/bidirectional), while also offering differential output for interference immunity. All our sensors have the same output capability and are interchangeable, provided they have the same number of pulses. An optional Z-marker (flag) pulse with a complementary signal can be used for zero-point reference.
Should the membrane on the sensor be removed?
No. That membrane is used to protect the sensor on the encoder. It helps retain the sensor sealing material during manufacturing and adds protection to the sensor surface.
Why did I order a 1024ppr pulse wheel, but it actually read 512ppr?
To help our customers standardize their inventory, we use common basic counts of 480, 512, and 600 pulse wheels to obtain pulse counts from 60 to 1200 ppr.
What type of cable should I use to connect the encoder?
You should use twisted pair/shielded cable such as Belden 9728 or 9730, 18 or 22 AWG (depending on the length required).
Do I need to shut down my motor or machine to change the NorthStar sensor?
Some devices require shutdown, and speed feedback will be lost when the connector is disconnected. The best way to minimize downtime is to reserve sensor positions for dual-output encoders (if applicable). NorthStar sensors are designed for quick connection/disconnection and replacement.
How do I set my calibration constant?
To determine the installation requirements, we need the motor manufacturer, frame size, AC or DC, cooling (if applicable), shaft size, and the required mounting: either at the drive end or the other end of the drive.
How to perform fault detection on a NorthStar encoder?
Encoder fault detection requires an oscilloscope or a NorthStar M100 encoder tester to test the sensor's output waveform. The encoder's specifications are detailed in the instruction manual. These specifications include phase and duty cycle. If the sensor is outside the specified range, you should check the pulse wheel for alignment. Refer to the instruction manual or call a NorthStar product expert for more details.
Will cracks, gaps, or scratches on the pulse wheel affect the output of the NorthStar encoder?
Depending on the severity and location of the damage, this may result in pulse loss.
Do you have converters that can convert digital inputs to analog outputs?
Yes. Dynapar's FV2 is a frequency-to-voltage device that, according to customer specifications, can provide 0-10V or a current loop output of 4-20mA.
Are NorthStarRIMTach® or SLIMTach® sensors repairable?
No, they cannot be repaired. Our sensors are electronically packaged to prevent them from being damaged in harsh environments.
Are NorthStarRIMTach® or SLIMTach® encoders repairable?
We can repair bearings and shafts for the RIMTach® 6200. Other RIMTach® and SLIMTach® products require sensor replacement. Pulse wheels can also be replaced. Contact NorthStar product experts for more information.
What should I do if I need to install the wheel onto the shaft coupling speed meter?
The RIMTach® 6200 is designed for foot-mounted applications and retrofitting of older analog speedometers, such as the BC42 and BC46GE speedometers.
What should I check if the NorthStar encoder has no output?
Please confirm: The device is powered on. The sensor is not broken. The pulse wheel is aligned. There is no short circuit between power and ground. The pulse wheel uses a matched sensor.
Note: The pulse wheel and sensor must be compatible (i.e., a 512 pulse wheel with 64, 128, 256 , 512, 1024 sensors or a 600 pulse wheel with 75 , 150 , 300 , 600 , 1200 sensors), and (must be a multiple of 2).
What are some potential solutions for dealing with noisy signals?
Please confirm that the shield of pin 10 is connected to the driver's shield. Grounding pin 10 can sometimes help with signal clarity in pulse wheel pairs. Cable pairs must be grouped with complementary signals (i.e., A , /A pair, B , /B pair, Z , /Z pair, Vcc, Com pair) and correctly connected to the terminals. If all of this does not work, call a NorthStar product expert for assistance.
My NorthStar encoder is having intermittent malfunctions. What should I check?
Check: Align the pulse wheel. Confirm whether the motor shaft has axial movement. Check if the ambient temperature exceeds 90 degrees Celsius.
What should I do if the shaft on the NorthStar pulse wheel is loose and slipping?
This should not happen unless the screw is not tightened or the torque is exceeded, in braking applications. The holes drilled for the locating screws must match the shaft.
If the Z signal cannot be detected on a NorthStarSLIMTach® product, what is the most likely possibility?
If the gap between the wheel and the SLIMTach® frame near the sensor is greater than 0.006 ", the sensor will not pick up the Z pulse. Check the concentricity of the C-face. Use an M100 encoder tester to detect this type of problem. If you are testing Z marks, the M100 tester must be set to Option 3 position signal type or it will not be able to recognize the Z pulse.
