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Absolute Encoder Options and Features

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Custom Models Logic Output Formats Resolution
DataReady Signal Output Circuits Output Connections Rotation
Interrogation Rate Output Codes Supply Voltages  

 

Output Codes

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View FileDatasheet

Absolute encoders generate multi-bit codes that represent the angular position of the shaft using one of the following formats:

  • Gray Code
  • Natural Binary
  • Excess 76 Gray Code - 360 count (call for details about this output code)
  • Others are available on special request, such as BCD

 

Output Formats

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The output code is produced by the absolute encoder in either parallel or serial formats.

Parallel

One encoder connector pin is used to output each bit of resolution. For example, an 8-bit encoder uses 8 pins to generate the output code.

Serial synchronous

The output code is output on one connector pin using a predefined format and clocked out at a rate given to the encoder on a clock input pin.
View FileDatasheet

Analog

The output position is converted to a 0-10vdc voltage

 

Output Connections

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View FileDatasheet

The datasheet shows the pin functions for the DB25 and MS3102E20-20P connectors and other useful information. See the SR12 Datasheet for all SR12 output connections.

 

Supply Voltages

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The following supply voltage options are available for the R30 and SR30:

  • 5 vdc ± 5%
  • 8 to 28 vdc

Supply voltage for the MR30 is 5 vdc ± 5%.

The following supply voltage options are available for the SR12:

  • 5 vdc ± 5% vdc for digital output models
  • 12 to 30 vdc for analog output model

 

Resolution

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Refers to the number of unique output positions for one revolution of an absolute encoder shaft. For example with a 360 resolution encoder, one revolution of the shaft is divided into 360 equal size segments of 1º each and numbered from 0 to 359. Continuously rotating the shaft in one direction results in successively outputting the same values 0 through 359, once per revolution. This is referred to as a single-turn absolute encoder.

The following shows the available resolutions for each absolute encoder model:

  • MR30: 256, 512, 1024, 2048
  • SR12: 128, 256, 512
  • SR30: 256, 512, 1024, 2048
  • R30: 256, 360, 512, 1000, 1024, and others

 

Interrogation Rate

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The rate at which the absolute encoder code disk is sampled. Regardless of rotational speed, this determines the maximum rate the outputs change.

Model Rate
R30 with Gray Code Continuous
R30 with Natural Binary 40K Hz
MR30, SR12, SR30 1K Hz
MR31, SR31 3K Hz

 

Logic

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Refers to the output voltage levels that are interpreted as binary values for absolute encoders. For example, with positive logic an output of zero volts is to be interpreted as a binary "0" value, and an output approximately equal to the input supply voltage is to be interpreted as a binary "1". This interpretation must be followed regardless of the output circuit type used. In particular with a current sinking or open collector output circuit, when the output transistor is "on" the output voltage is zero volts, and therefore should be interpreted as a binary "0".

Logic "0" Value "1" Value
Postive 0 vdc Supply Voltage
Negative Supply Voltage 0 vdc

 

Rotation

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As a standard convention on Photocraft absolute encoders, counts increase with clockwise rotation as viewed from the shaft end. Decreasing counts are available on some models. Selectable direction is available on some R30 models.

 

DataReady Signal

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For output codes other than gray code, more than 1 output bit can change as the encoder shaft is rotated from one position to another adjacent position. For example with a 256 resolution natural binary encoder, as the shaft rotates from position 255 to position 0, all 8 bits of the output change. In this case it is not possible for the encoder to guarantee that all output bits change simultaneously, rather there is a period of several micro-seconds during which individual output bits are changed independently. Reading the outputs during this period should be avoided. The DataReady output can be used to determine when outputs are changing - it is normally high and goes low to indicate the outputs are changing. An optional low DataReady is available on some models.

 

Output Circuits

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0-10vdc Analog - The digital position is converted to a 0-5vdc analog signal using a digital to analog converter. That signal is then amplified to a 0-10vdc signal using an OPA251 op amp. RS422
Current Sinking - An NPN transistor with a pull-up resistor and capable of sinking either 5ma or 50ma of current per output, depending on model number. Current Sinking
Current Sourcing - A PNP transistor with a pull-down resistor and capable of sourcing 50ma of current per output. Current Sourcing
Open Collector - An NPN transistor without a pull-up resistor and capable of sinking 50ma of current per output. An external pull-up resistor must be used. This output type is typically used when the encoder and the device receiving the encoder's output are operating at different supply voltages, or if the control device, such as a PLC, includes its own pull-up resistor. Caution: the output must not be pulled-up more than 30 vdc, and both supplies must reference the same common. Open Collector
Push/Pull - A general purpose circuit capable of either sourcing or sinking up to 5ma of current per output, and is compatible with most motion control equipment. Push/Pull

 

Custom Models

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Photocraft manufactures many modified versions of our standard products to meet specific application requirements. Custom versions of our standard products could include any of the following:

  • Shaft lengths, diameters, or modifications such as flats and keyways.
  • Mounting configurations and adapters.
  • Output circuits and formats
  • Software features such as custom output codes
  • Cables and connectors
  • Private labeling

For economical solutions to your special encoder needs, allow our engineers to work with you to design a product that exactly meets your requirements.