Incremental
Absolute
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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 |
The output code is produced by the absolute encoder in either parallel or
serial formats.
| Parallel |
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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. |
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| Serial synchronous |
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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. |
Datasheet
(47k) |
| Analog |
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The output position is converted to a 0-10vdc voltage |
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The datasheet shows the pin functions for the DB25 and MS3102E20-20P
connectors and other useful information. See the SR12
specifications for all SR12 output connections.
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 |
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 |
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 |
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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 |
| Positive |
0 vdc |
Supply voltage |
| Negative |
Supply voltage |
0 vdc |
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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.
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.
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.
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