ENC2 Linear Position v2

Provides the current position as measured from encoder edges. There are four encoder edges per pulse; A, B, /A, and /B. The position is 100% when the number of received edges in the forward direction equals 4 times the PPR parameter, times the Base Revs parameter.

Inputs are provided for reversing the direction, resetting the position to zero, choosing the power-up position, and Hold, i.e. ignoring counts.

Click the Internal Count button to view the raw number of edges that have been counted. Four parameters provide a 64-bit count with the most significant digits in Count 3 and the least significant digits in Count 0.

Interesting Note - A 64-bit position line is very large. A 5000PPR encoder running at 5000RPM will take over 350,000 years to reach the end of the number line! Assuming this was possible, the smarty could still find the exact edge of the starting position.

• Available only in the dw2xx series products
• Requires library: Encoder Control (option -11)
• Requires: Dual Encoder
• Singleton function block
• Firmware versions 0x2027 and later

• 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.
  
  
• Open circuit on the input channels.
  
  
• -10 V < Common Mode Voltage < 13.2 V
  

  
  
  

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

  
  
• | Differential Voltage | < 275 to 475 mV
  

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

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

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.

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

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

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.

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