Encoder
ENC2 Linear Position
Description This function block is used to count pulses on the appropriate encoder channel. The count isinternally stored as a 64-bit number and increments with each transition of each encoder channel(i.e., the actual count for one revolution of the encoder will be four times the pulses perrevolution of the encoder).
Availability
  • Available only in the dw2xx series products
  • Requires library: Encoder Control (option -11)
  • Requires: Dual Encoder
  • Singleton function block
  • Firmware versions 0x2008 through 0x2026
savvy-SFD Graphic enc2p5
Graphic with Parameters enc2p5

Parameters

Status Internal Parameter, Read-only, Enumerated (signed 16-bit integer)

For proper operation, the Status parameter must read OK. The parameter indicates:
  • The presence of input channels A, B, and their complements.
  • The status of communications to the external encoder module (if present).

When the Status changes to a faulted state, the internal ENC# Position Block count is held at its last value until the status returns to an OK state. If a fault clears, the Status will immediately return to OK (i.e., fault conditions are not latched).

For critical or sensitive applications, a drive.web connection may be made from the Status parameter to logic designed to handle a faulted encoder.

Possible causes for Fault on A, Fault on B, Faults on A and B are shown below:

  • Short circuit between input channels.
    enc_short_circuit
  • Open circuit on the input channels.

  • -10 V < Common Mode Voltage < 13.2 V

    enc_cmv_low enc_cmv_high

    The CH3 signal going high results in the Status parameter changing to a faulted condition.


  • | Differential Voltage | < 275 to 475 mV
    enc_diff_voltage

    The CH2 signal going high results in the Status parameter changing to a faulted condition.

If the Status parameter indicates a Comms Fault, there may be extreme radio frequency(RF) noise coupling to your smarty2 I2I signal wires, a wiring fault, or a hardwarefault. Check for proper shielding and routing of cabling.
0 = OK
1 = Fault on A
2 = Fault on B
3 = Fault on A and B
4 = Comms Fault
Pulses Per Revolution Input, Read-write, Analog (signed 16-bit integer)
1 ppr to 30000 ppr

The Pulses Per Revolution (PPR) parameter calibrates the ENC# Position block for theattached incremental encoder. Usually, this parameter is easily determined from the model numberand is typically a power of 2 (e.g., 210 = 1024, 211 = 2048, or212 = 4096). Generally, the higher the PPR, the more precise motion profile than can beachieved.

The Pulses Per Revolution (PPR) parameter is used with the Base Revs parameter toscale the Output parameter as follows:

Output % = [Internal Position Count / (4 * Pulses Per Revolution * Base Revs)] * 100
Base Revs Input, Read-write, Analog (unsigned 16-bit integer)
1 to 65535

The Base Revs parameter calibrates the ENC# Position block for 100% output when thedesired number of revolutions is achieved. The Base Revs parameter is used with thePulses Per Revolution parameter to scale the Output parameter as follows:

Output % = [64-bit Internal Position Count / (4 * Pulses Per Revolution * Base Revs)] * 100

The larger the Base Revs the lower the resolution of the Output; however, too small a Base Revs will quickly result in an overrange on the Output (i.e., either 327.67 % or - 326.67% depending on direction). Generally, it is good practice to set the Base Revs at just above the maximum expected number of revolutions and then use multiple instances of the ENC Position Monitor with the appropriate scaling for control purposes.

Even if an overrange is indicated, the internal 64-bit value is maintained and updated and still available for use with other encoder count type function blocks. If the Output comes back into range, the current percentage will be displayed.
Count 0 Internal Parameter, Read-only, Hexadecimal (unsigned 16-bit integer)
0x0 to 0xFFFF
Count 1 Internal Parameter, Read-only, Hexadecimal (unsigned 16-bit integer)
0x0 to 0xFFFF
Count 2 Internal Parameter, Read-only, Hexadecimal (unsigned 16-bit integer)
0x0 to 0xFFFF
Count 3 Internal Parameter, Read-only, Hexadecimal (unsigned 16-bit integer)
0x0 to 0xFFFF
Persistence Internal Parameter, Read-write, Boolean (signed 16-bit integer)

The Persistence parameter defines the behavior of the 64-bit internal count when the moduleis powered down. By default the internal count is reset to zero at power-up. If you would like thevalue to be stored at power down, change to Persistent.
0 = Clear on power-up
1 = Persistent
Sign Input, Read-write, Boolean (signed 16-bit integer)

The Sign parameter is used in conjunction with the encoder wiring (A with respectto B channel) to determine the count direction.

Behavior of the internal 64-bit count is defined below:

Sign Direction Internal Count
Positive Forward Increments
Positive Reverse Decrements
Negative Forward Decrements
Negative Reverse Increments

The Sign parameter can be controlled by logic to change the behavior of the count which directly affects the Output parameter.


0 = Positive
1 = Negative
Reset Input, Read-write, Boolean (signed 16-bit integer)

When asserted, the Reset parameter resets the 64-bit internal count to zero.
0 = Inactive
1 = Reset
Output Output, Read-only, Analog (signed 16-bit integer)
-327.67 % to 327.67 %

The Output parameter is generated from the 64-bit internal count as follows:

Output % = [Internal Position Count / (4 * Pulses Per Revolution * Base Revs)] * 100

If the Output exceeds +/- 327.66%, the parameter will indicate overrange; however, the 64-bit internal count is unaffected.


-32767 = - overrange
32767 = + overrange
Direction Output, Read-only, Boolean (signed 16-bit integer)

The Direction parameter indicates the relationship of encoder channel A with respectto encoder channel B.

To invert the behavior of the Direction parameter, swap the A and not A signals at the input terminals.
0 = Forward
1 = Reverse