Frequently Asked Questions (Encoder FAQs)
Click a question to jump to the answer:
What is a Differential Line Driver Output?
Answer: A differential output refers to the fact that each channel has a complement channel, i.e. Channel A and Channel A not. A differential line driver is used to help increase noise immunity (see What are the A not and B not Channels used for?). A differential line driver also allows you to sink or source more current than a Totem Pole output. A differential line driver will work both with a sinking or sourcing circuit. (see What is a Sinking or Sourcing input?) It can also help in increasing the distance in which a signal is transmitted.
What is an Open Collector Output?
Answer: An Open Collector output is an NPN transistor. An NPN transistor allows the sinking of current to common. It can be thought of as a switch that allows the circuit, after the load, to be connected to common. This means that a source is required for the output to work. A supply through a load must be connected to the output,
otherwise the NPN transistor is simply creating a path to common, i.e. a dry contact. Therefore, if you were to measure the voltage at the output of an open collector that is not hooked up to some supply you would not see a change in voltage. The voltage should be measured across the output load to determine if the open collector is working properly.
Back to topWhat is a Totem Pole Output?
Answer: A Totem Pole output is essentially the same as a Push-Pull output; however, it is the terminology commonly used when referring to a TTL device. The major difference between it and a Push-Pull is the amount of current that it can sink or source. The Totem Pole output is going to sink/source less current then a Push-Pull output is capable of sinking or sourcing. The other major difference is the output voltage between the two. The Totem Pole is a 5V DC signal only, where the Push Pull will follow the input voltage.
Back to topWhat is a Push-Pull Output?
Answer: A Push-Pull output is an output that allows you to connect either a sinking or sourcing circuit. (see What is a Sinking or Sourcing input?) This type of an output allows you to sink more current than a Totem Pole output and follow the input voltage. A Push-Pull output is chosen when an Open Collector output will not work with the controller that is connected to the encoder.
Back to topWhat is a Quadrature output?
Answer: Quadrature output refers to the fact that the signals A and B are separated by 90 degrees of phase shift with A leading B or B leading A depending on the direction of rotation. It does not mean that the output will be 4 times the amount of the Pulses Per Revolution of the encoder. The fact that the signals are 90 degrees out of phase enables the controller to determine the direction that the encoder is spinning. You must use both the A and B signal to have a quadrature output and to get X2 or X4 logic. (see What is the difference between Quadrature and x4 Logic?)
Back to topWhy do I need a pull-up resistor?
Answer: A pull up resistor is used to "pull" the logic high voltage level up to the level of the operating voltage. This is useful when the output of the Open Collector is not reaching the voltage level needed to indicate a logic high signal or when noise is present on the signal line. When a logic high signal is present its voltage level will be approx. that of the operating voltage for an open circuit. The difference is due to the voltage drop across the pull-up resistor. This is not necessarily true if the load is referenced to ground.
Back to topWhat are the A not and B not Channels used for?
Answer: The A not and B
not channels are the compliments of the A and B channels. This means that when signal A is high, signal A not is low and when A is low, signal A not is high. The same is true for any signal that has a compliment. This is commonly used to keep noise to a minimum. Some input cards will accept both the A and A not signal. It then compares the two signals to help eliminate common mode noise that may have been picked up on the line. This is done by accepting a pulse only when signal A is high and signal A not is low. This is true for any channel that has a compliment, signal A was used only as an example. This is commonly called a Differential Output.
Back to topWhat is the difference between Quadrature and x4 Logic?
Answer: Quadrature output refers to the phasing of the output signals. When the output signals, signal A and B, are 90 degrees out of phase with each other, the output is said to be in quadrature. This is the only thing that the term quadrature implies. (see What is a Quadrature output?)
x4 Logic denotes how the controller will interpret the signal that it is receiving. This is done by translating each edge of the pulse detected for the A and B channel into its own pulse. This translation takes place in the controller and not at the encoder.
This means if you order a quadrature encoder with 120 pulses per revolution, the output of signal A and B will be out of phase by 90 degrees. It does not mean that for every one revolution that the encoder makes you will get 480 pulses. The multiplication of the pulses only occurs at the controller.
Back to topHow do I choose the Pulses Per Revolution (PPR)?
Answer: When choosing the PPR value of the encoder, please keep a few simple rules in mind. Make sure that you do not choose a PPR that will cause you to exceed the maximum frequency of your controller or encoder. Try to choose a PPR that is close to the value you wish to display, this eliminates or reduces the need for a calibration constant. For example, If you wish to display 12 inches for every revolution choose a PPR of 12. If you wish to display 12.00 inches, choose 1200 PPR. However, do not make the mistake of forgetting the multiplication of the controller's input. Most controllers have X2 or X4 logic. If it is X2 logic, this would change your PPR to 600 for a 12.00 display; and the PPR would be 300 for X4 logic. These choices give you one pulse for every one unit of measurement desired. It is important to remember the frequency that your PPR will create. When choosing the PPR, do not choose one that will result in a higher frequency than the encoder can handle at your max. speed. The reverse is also true, do not choose too low of a PPR, that your controller cannot recognize the signal. Try to choose your PPR so that your calibration constant is between .5 and 1.
How do I set my Calibration Constant?
The calibration constant can be simplified by simply selecting the correct Pulses Per Revolution (PPR). Once the PPR has been selected or is known simply follow the formula presented in the Technical Manual. When choosing your calibration constant remember the closer to 1 the better. The value of the calibration constant is your best resolution per pulse of the encoder.
Back to topHow far away can I place my Dynapar encoder from my system?
Answer: There is no set answer to this question. Many factors play a role in determining the maximum length of cable that can be used to connect the units together. The largest problem with running long lengths of cable is that the cable becomes more susceptible to noise. This is due to the capacitance of the cable, the cable acting as an antenna, and the loss of power through the cable. The maximum distance of cable can be achieved by following some basic wiring principles. Do not run the cable near objects that create a lot of electrical noise. This includes AC motors, Arc welders, AC power lines, and transformers. Use twisted pair cabling when using the signal and its complement, and shielded cabling when running any type of signal. Use the highest voltage available for the output voltage. For example, if the encoder will output 5 to 24 volts, then use 24 volts. Use an Open Collector or Differential Line Driver output with a differential receiver (PM28S00) so that the maximum amount of current can be sink/sourced.
If you are using the encoder as an input to more than 1 controller, use a signal amplifier. This is also a good way to help increase the distance a signal can travel. Typical maximum distances for a Differential Line Driver are around 100 ft.or more when using a differential input, and for an Open Collector the distance is around 35 ft.
Back to topWhat is a Zero Speed sensor?
Answer: A zero speed indicator is a separate output used as an alarm when the speed of the application drops below a certain frequency, not when zero speed occurs. The zero speed is not detected, only the drop below a set frequency can be detected. This is useful when the speed of the application is critical and must be monitored.
Back to topIs shielded cable needed?
Answer: YES. The use of shielded cable is highly recommended. This is especially true for areas in which large amounts of electrical noise exist. If you are having any noise problems, or suspect that you might, then use a shielded cable.
Back to topWhy use an absolute encoder?
Answer: First, what is an absolute encoder? An absolute encoder has each position of the revolution uniquely numbered. This means that instead of an output of pulses, you get an output that is a specific value in a binary format. This is very useful when exact positioning is a must. Since each location in an absolute encoder's revolution is a unique binary value, if the power should be lost, the actual value of the position will be known when power is restored. The exact position will be known even if the controller loses power and the process is moved.
Back to topWhat is Gray Code?
Answer: Gray Code is a form of binary. The difference between Gray code and binary is the method of incrementing to the next number. In Gray Code, only one digit may change states for every increment. This means the count sequence would look something like this 0,1, 3, 2, 6, and 7. This is different than standard binary, where the sequence would be 0, 1, 2, 3, 4, and 5.
Gray Code Binary
0000 0 0000 0
0001 1 0001 1
0011 2 0010 2
0010 3 0011 3
Gray Code is used to prevent errors as transitions to the next state occur. An example of how an error could occur would be where both values in the sequence were true. This can occur due to the timing sequence and the capacitance of the cable. The transition from 0011 to 0100 could cause 0111 to be generated, with Gray code this is not possible.
Back to topHow do I convert Gray code to Binary?
Answer: The conversion from Gray Code to binary is simple.
Step 1
Write the number down and copy the
left most digit under itself. (1 1 0 1 1 Gray Code = 1 Binary)
Step 2
Add the highlighted binary digit to the Grey code immediately up and to the right of it. So 1 plus 1 is 0 dropping the carry. Write the result next to the binary digit just added. Drop all of the carried digits. (1 1 0 1 1 Gray Code = 1 0 Binary)
Step 3
Repeat Step 2 until the number is completed.
1 1 0 1 1 Gray Code
1 0 0 Binary
1 1 0 1 1 Gray Code
1 0 0 1 Binary
1 1 0 1 1 Gray Code
1 0 0 1 0 Binary
Back to topWhat is a Sinking or Sourcing input?
Answer: Sinking and Sourcing inputs simply refer to the current flow in a transistor. This means that they require a voltage and a load to operate. A sinking input requires the voltage and load to be present before connecting it to the circuit. This means that it is "sinking" the current to ground for the circuit. A sourcing input must be before the load in the circuit. This means that it is "sourcing" the current to the circuit. Voltage and a load must be present in either case to detect a voltage change at the input. The same is true for sinking or sourcing outputs.
NorthStar brand FAQs
Are NorthStar encoders able to provide a 26V output?
Answer: Yes, we have designed a new generation of sensors that will soon be available in all of our RIM Tach® and SLIM Tach® products.
Back to topDo the NorthStar sensors provide a quadrature, bi-directional, or Z marker output?
Answer: Yes, all of our sensors are capable of providing a speed and directional feedback signal (quadrature/bi-directional), as well as noise immunity (differential output). All of our sensors are packaged with the same output capability and are interchangeable as long as they are within the same pulse family. An optional Z marker (index) pulse with its complement is also available for zero referencing.
Back to topShould the tape on the sensor be removed?
Answer: No. The tape is applied to the sensor on our encoders for protection. It helps keep the sensor encapsulant from getting on the sensor during curing and is added protection on the sensor face.
Back to topWhy does my pulse wheel read 512 ppr when I ordered a 1024 ppr?
Answer: To allow our customers to standardize their inventory, we use common pulse wheels with a base count of 480, 512, and 600 to derive pulse counts from 60-1200
ppr.
Back to topWhat type of wire should I use to wire the encoder?
Answer: You should use twisted pair/shielded cable such as Belden 9728 or 9730, 18 or 22 AWG (depending on the length needed).
Back to topDo I need to shut down my motor or machine to change out NorthStar sensors?
Answer: Some units will require shutdown due to loss of tachometer feedback when the connector is disconnected. The best way to reduce downtime is to keep a space sensor in a dual output encoder (if applicable). NorthStar sensors are designed for quick connection/disconnection and replacement.
Back to topWhat information do you need to determine the type of NorthStar encoder best suited for an application?
Answer: To determine the mounting requirements, we need the motor manufacturer, frame size, AC or DC, cooling (if any), shaft size, and required mounting: drive-end or opposite drive end.
How do I troubleshoot a NorthStar encoder?
Answer: Troubleshooting an encoder requires an Oscilloscope or a NorthStar M100 Encoder Tester to test the output waveform of the sensor(s). The specifications for encoder operation are in the instruction manual. The specifications consist of phase and duty cycle. If the sensor is not within specification, you should check the alignment of the pulse wheel. Follow the instruction manual or call a NorthStar Product Specialist for more details.
Back to topWill a nick, chip, or a scratch on the pulse wheel affect the output of my NorthStar encoder?
Answer: Depending on the severity and location of the damage, it may cause missed pulses.
Do you have a converter that will take a digital input and give an analog output?
Answer: Yes. Our FV2 by Dynapar unit is a frequency to voltage unit capable of providing a 0-10V or a current loop output of 4-20mA configured to customer specifications.
Are the sensors repairable in the NorthStar RIM Tach or SLIM Tach products?
Answer: No, they are not repairable. Our sensor electronics are encapsulated to prevent them from damage in harsh environments.
Back to topAre the NorthStar RIM Tach or SLIM Tach encoders repairable?
Answer: We are able to repair the bearings and shaft on the RIM Tach® 6200. Other RIM Tach® and SLIM Tach® products require sensor replacement. Wheels can also be replaced. Contact a NorthStar Product Specialist for more information.
What if I need a wheel mounted on a shaft-coupled tachometer?
Answer: The RIM Tach® 6200 is designed for foot mount applications and retrofitting older analog tachometers such as the BC42 and BC46 GE Tachometers.
Back to topWhat do I check if I have no output on a NorthStar encoder?
Answer: Make sure: The unit is powered. The sensor is not cracked. The wheel is aligned. There are no shorts between the power and ground. The wheels are used with the proper sensors.
NOTE: Wheels and sensors must be compatible (i.e. 512 wheel w/ 64, 128, 256, 512,1024 sensor or 600 wheel w/ 75,150,300,600, 1200 sensor). *Must be in multiples of two.
Back to topWhat is a potential solution for a noisy signal?
Answer: Make sure: The shield wire pin 10 is hooked to the shield on the drive. Grounding pin10 sometimes helps in the signal clarity.
The wheel is aligned.
The pairs of wire are grouped with their complements (i.e. A, /A pair, B, /B pair, Z, /Z pair, Vcc, Com pair) and that they are properly connected at the terminal.
If all else fails, call a NorthStar Product Specialist for termination information.
Should my NorthStar encoder have intermittent failures, what should I do to check?
Answer: Check: The alignment of the wheel.
To be sure the shaft is not moving axially on the motor.
To see if the encoder ambient temperature is above 90 degrees C.
Back to topWhat do I do if the wheel breaks loose on the NorthStar encoder shaft and is slipping?
Answer: This should not happen unless the screws were not tightened properly or there is an over torque problem, as with braking applications. Drill or punch holes where the set screws meet the shaft.
If there is no Z signal on a NorthStar SLIM Tach product, what is the most probable cause?
Answer: If the gap between the wheel and the SLIM Tach® frame near the sensor is greater than .006", the sensor will not be able to pick up the Z pulse. Check C-face concentricity. Use the M100 Encoder Tester to check for this type of problem. If you are testing for a Z marker, the M100 Encoder Tester must be in the option 3 position signal type or it will not be able to recognize the Z pulses.
How will chipped wheels or cracked sensors affect the output of my NorthStar encoder?
Answer: Damage to the pulse wheel may or may not affect the output of the encoder or may cause intermittent problems. Do not drop the sensors or the pulse wheels. All threaded rods should be used as guides when taking the encoder housing off of the 8500. Make sure the sensor modules are removed when the housing is removed or installed on the motor.
