Encoder FAQs

All measurements are a rough approximation of the “true” value, meaning that the measured value always has a certain amount of error from the “true” value. The size of such an error is what is commonly referred to as the measurement accuracy, which reflects the measurement The ability of the instrument system to faithfully reproduce the measured signal value.
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What is the encoder?
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Encoders are devices that convert angular or linear displacements into electrical signals. The former is called code wheel, the latter called yardstick. According to read out the encoder can be divided into contact and non-contact two. Contact using brush output, brush contact conductive area or insulation to indicate the status of the code is “1” or “0”; non-contact to accept the sensitive element is a photosensitive element or magnetic sensor, Light and opaque areas to indicate whether the status of the code is “1” or “0”.
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According to the principle of encoder can be divided into two types of incremental and absolute. Incremental encoder is the displacement is converted into periodic electrical signals, then the electrical signal into a count pulse, with the number of pulses that the size of the displacement. Each position of the absolute encoder corresponds to a specific digital code, so its indication depends only on the start and end position of the measurement, regardless of the intermediate process of the measurement.
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Definition of measurement accuracy?
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As we all know, all the measurements are rough estimates of the “true” value, that is, the measured value always has a certain error from the “true” value. So the size of such an error is what is commonly called the measurement accuracy Reflects the ability of the measuring instrument system to faithfully restore the measured signal value.
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Incremental encoder accuracy?
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Incremental optical encoder accuracy and resolution have nothing to do, which is two different concepts. Accuracy is a measure of the ability to determine the position of any pulse relative to another pulse at a resolution selected. Accuracy is usually expressed in terms of angle, angle or angular seconds. The accuracy of the encoder is related to the quality of the machining of the light-transmitting slit of the code wheel and to the manufacturing accuracy of the mechanical rotation of the code wheel, and to the installation technique.
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Incremental encoder resolution?
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The resolution of a photoelectric encoder is expressed in terms of the number of basic cycles of the output signal produced by the revolution of the encoder shaft, namely the number of pulses / revolution (PPR). The number of light-transmitting slits on the code wheel is equal to the resolution of the coder. The more the slits engraved on the code wheel, the higher the resolution of the coder. In the industrial electric drive, depending on the application object, you can choose incremental optical encoder usually 500-6000PPR resolution, up to tens of thousands of PPR. AC servo motor control system is usually selected with a resolution of 2500PPR encoder. In addition, the photoelectric conversion signal is processed logically, you can get 2 times or 4 times the frequency of the pulse signal to further improve the resolution.
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What is the relationship between absolute encoder resolution and resolution?
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The number of lapped absolute encoders represents the number of code tracks on the code disc. Because it uses a binary codec (the same Gray code), its accuracy becomes a factor of 2, such as 12, which is 2 12th power is 4096.
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Encoder resolution and accuracy are not necessarily the same accuracy with the score, mechanical concentricity encoder, the reading response speed, temperature characteristics and other factors. If an encoder is engraved with a sine wave subdivision high resolution, then it does not improve the accuracy, subdivision only increase the resolution. Before the subdivision of the number of scribing accuracy, subdivision accuracy or how much, so some of the high resolution of the encoder depends on the accuracy of how many lines prior to subdivision.
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Second, Hengstler brand
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Through the SSI interface, the maximum frequency of data polling how to determine?
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The following “best case” and “worst case scenario” must be considered for the current position data transmitted via SSI.
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The output of the position data depends on several parameters such as: factor, conversion time, data format and so on. Therefore, the processing time will be different.
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With a processor system you will “get” only one average response time. If you poll the SSI channel using the highest frequency of 500kHz. That is, (pulse time 2 μs * 26 bits + minimum required pause time 40 μs) is the shortest time approximately 100 μs. Since then, the system will require an additional 400-500 s of time for data updates, so you may get the same result (location value) three times in the worst case! You can achieve shorter times (factor of 10) using faster DSPs or ASICs, or encoders with SIN / COSINE codec applied to the motor control system.
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What is the difference between AC59 and AC61?
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Both types of encoders are stainless steel. The “61” is equipped with a solid, sturdy stainless steel housing and is attached to a stainless steel flange. Standard cable accessories are made of nickel-plated brass. “This design allows for complex encoder types such as absolute encoders with bus bonnets and guard-in access to the encoder’s interior, such as DIP switches.” The 59 “includes a deep-drawn stainless steel housing and a crimp Stainless steel flange connection. The standard cable accessories are made of PVC. “This design is usually less expensive (with a reduced number of encoder types required): Incremental encoder with cable connector with cable connector Absolute Encoders and Sealed Enclosures (eg Parallel Single Lap, SSI or BiSS).
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What is the difference between a solid shaft encoder and a hollow shaft encoder?
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Solid shaft encoders require mounting flanges and couplings. Hollow shaft encoders require only one spring leaf to prevent encoder rotation and vibration absorption.
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What GSD files do you need to use when using ACURO encoders?
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ACUROAC58 Series Encoder You can use the same GSD files as the RA58 series. The reason is: If the RA58 is broken, the user will replace it with AC58. If the code of the encoder is not the same, the PLC (GSD file identification used) will not be able to connect to the AC58 encoder replacing the RA58, so the PLC software must be modified. We made the same is to make the user application more convenient.
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Third, Dynapar brand
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What is differential line driver output (DifferentialLineDriverOutput)?
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Differential output refers to the fact that each channel has a complementary channel, such as A and / A. Differential line drivers can help improve noise immunity (see / A and / B channels for what?). Differential line drivers also allow you to output more drain or source current than push-pull. Differential line drivers have both leakage and source circuitry to work together. (See What Is a Drain or Source Input?) It can also help increase the signal transmission distance.
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What is the OpenCollectorOutput?
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An open collector output is an NPN transistor. NPN transistors allow leakage current to the common terminal. It can be thought of as a switch that allows the circuit to be connected to a common terminal after it has been loaded. This means that you need a power supply if you have output. The power supply must be connected to the output load, or NPN transistor is to establish a path to the common end, that is dry contact. Therefore, if you measure an open collector output voltage that is not connected to any power supply, you will not see a voltage change. If the open collector is working properly, the voltage should be detected after the output load.
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What is totem pole output (TotemPoleoutput)?
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The totem-pole output is basically the same as the push-pull output, but it is a common term when it comes to TTL devices. The main difference between it and the push-pull output is the size of the drain or source current. Totem-pole output than push-pull output leakage / source current is smaller. The other major difference is that the output voltage is different. The totem-pole can only be a 5V DC signal, and the push-pull output will follow the input voltage.
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What is PushPullOutput?
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Push-pull output is an output that allows you to connect a drain or source circuit at the same time. (See What Is a Drain or Source Input?) This type of output allows you to output more current and follow the input voltage than the totem-pole. When the open collector output and the encoder connected controller can not work, you need to select the push-pull output.
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What is quadrature output (Quadrature output)?
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Orthogonal output refers to a 90 degree phase shift between signals A and B, and A leading B or B leading A depends on the direction of rotation. This does not mean that the output will be 4 times the encoder’s resolution per revolution. The fact that the signal has a 90 degree phase difference allows the controller to determine the encoder’s direction of rotation. You must use orthogonal A and B signals in order to get the logic of X2 or X4. (See What is the difference between Orthogonal and x4 Logic?)
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Why do I need a pull-up resistor?
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Pull-up resistors are used to “pull” logic high voltage levels up to operating voltage. This is useful when the open-collector output does not meet the voltage level or noise level required to show a high logic level on the signal line. When a logic high signal appears, its open collector voltage level is approximately equal to the operating voltage. The difference is due to the voltage drop across the pull-up resistor. If the load is not for reference, this is not necessary.
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A and B channel what is the use?
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The / A and / B channels are the inverse of the / A and / B channels. This means that signal / A is low when signal A is high and / A is high when A is low. The same applies to any situation where there is a complementary signal. This usually minimizes noise. Some input cards accept both A and / A signals. The two signals are then compared to help eliminate common-mode noise propagating on the wire. The received pulse is acknowledged only when signal A is high and signal / A is low. This applies to any channel with complementary signals, signal A is only an example. This is commonly referred to as differential output.
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What is the difference between quadrature and x4 logic?
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Orthogonal output refers to the phase shift of the output signal. When the signal is output, the signals A and B are 90 degrees out of phase with each other, which is called quadrature. This is only an orthonormal term explanation. (See what is quadrature output?)
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The x4 logic refers to how the controller interprets the received signal. This is done by converting the edge of each detected A and B channel pulse to its own pulse. This conversion happens at the controller, not at the encoder.
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This means that if you ordered 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 that the encoder will produce 480 pulses per revolution. The added pulse only happens to the controller.
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How to choose the pulse number per revolution (PPR)?
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When choosing the encoder’s PPR value, keep in mind a few simple rules. Make sure the PPR value you select does not exceed the maximum frequency of the controller or encoder. Try selecting PPR close to the value you want to display, thus eliminating or reducing the need for calibration constants. For example, if you want 12 inches per turn, select PPR 12. If you want to show 12.00 inches, choose 1200PPR. However, do not mistakenly forget the controller input multiplier. Most controllers have X2 or X4 logic. If it is X2 logic, it will change to 600 for your PPR when 12.00 is displayed, and 300 for PPR when X4 is logic. These choices give you only one pulse per unit you expect. Remember when you create your PPR, be sure to remember the frequency. When selecting PPR, the maximum speed can not exceed the frequency that the encoder can handle. The opposite is the case, please do not choose too low PPR, your controller does not recognize the signal. Try selecting your PPR so your calibration constant is between 0.5 and 1.
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How to set my calibration constant?
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Correct selection of the number of revolutions per revolution (PPR) simplifies the calibration factor. Once the PPR is selected, or just follow the formula in the technical manual. When choosing a calibration constant, keep in mind that the closer you get to 1, the better. The value of the calibration constant is the resolution of each pulse of your best encoder.
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How far can my Dynapar encoder and my system be?
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No fixed answer. Many factors work, and the maximum cable length that connects the devices together. The biggest problem with using long cables is that the cables become more susceptible to noise. This is due to the capacitance of the cable, which acts like an antenna, while losing power through the cable. The maximum distance of the cable can be obtained and some basic wiring guidelines must be followed. Keep cables away from objects that generate a significant amount of electrical noise. This includes AC motors, arc welders, AC power cords and transformers. Use twisted pair when using signals with complementary signals and shielded cables when using any type of signal. The maximum voltage allowed for output voltage use. For example, if the encoder can output 5 to 24 volts, then 24 volts is used. Use a differential line driver output with open collector or differential receiver chip (PM28S00) for maximum drain / source current source.
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If you are using an encoder as 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 differential line driver has a maximum distance of about 100 feet and the open collector distance is about 35 feet.
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What is a zero speed sensor?
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Zero speed indication is a separate output, the application when the speed is lower than a certain frequency as an alarm, not zero speed appears. Zero speed can not detect, only drop below a certain frequency can be detected. This is very useful when the application is critical and must be monitored.
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Need to use shielded cable?
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Yes. Shielded cable is strongly recommended. In particular, it is used in areas where there is a lot of electrical noise. If you have any noise problems or if you suspect you may have used shielded cables.
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Why use absolute encoder?
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First, what is an absolute encoder? Absolute encoders have unique encodings at every turn. This replaces the pulse output, you can get binary special value output. This is very useful when asked for the exact location. The absolute encoder has a unique binary value for each position on each revolution, and if the power is off, the actual value of the position can be discerned when power is restored. Even if the controller loses power and the process is moved.
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What is Gray code?
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Gray code is a form of binary code. The difference between a Gray code and a binary code lies in the method of incrementing numbers. There is only one change for each Gray code. This means that the order of counting will see 0, 1, 3, 2, 6 and 7. This is binary with the standard