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.

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?)

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.

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.

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.

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.

A single ended signal simply transmits an electrical signal, in the form of varying voltage (A, B, and Z pulses), over one wire while the other wire is grounded. Single ended is the most cost-efficient option to implement because fewer wires are required for transmitting multiple signals. However, single- ended signaling can create “noise” by design.

The most common cause of encoder failure is a warped/ bent shaft that is no longer sitting on the bearings properly, an issue also referred to as shaft run-out. A warped shaft adds stress to the internal bearings and may lead to bearing failure and eventual overheating of the encoder. Avoid encoder failure by ensuring proper installation. However, if you suspect shaft run-out in your encoder, use a dial indicator to help confirm whether or not the shaft is misaligned.

It very possible for our dual output encoders to have multiple PPRs. All NorthStar SlimTach encoders offer different PPRs. However, the NorthStar RimTach dual output encoders must be from the same PPR family. For example, an encoder with a 256 PPR can be paired with a 512 but not a 600.

Controllers detect which direction the encoder is rotating by comparing channels A and B to see which one comes first – this process is referred to as phasing. You can reverse phasing by swapping A and B channel. In doing so, you should also swap A- and B- channels.