Control Techniques Digitax ST Advanced User's Manual page 53

Parameter Keypad and
structure display
An incremental digital encoder or a SINCOS encoder without communications may have a marker channel. When this channel becomes active it may
be used to reset the encoder position and set the marker flag (Pr 3.31 = 0), or just to set the marker flag (Pr 3.31 = 1). The marker flag is set each time
the marker input becomes active, but it is not reset by the drive, and so it must be cleared by the user.
If Pr 3.35 is set to zero the marker system operates in a conventional manner and only resets the position (Pr 3.29 and Pr 3.30) and not the turns
(Pr 3.28) on a marker event. If Pr 3.35 is set to one the whole position (Pr 3.28 to Pr 3.30) are reset on a marker event. The full reset mode allows the
marker to give a form of registration where the marker event defines zero position.
The marker function only operates when Ab, Fd, Fr, Ab.Servo, Fd.Servo, Fr.Servo type encoders are selected with Pr 3.38.
Drive encoder turns bits / Linear encoder comms to sine wave ratio
3.33
Bit SP
Coding
Range 0 to 255
Default 16
Update rate Background read (Only has any effect when the drive is disabled)
This parameter has a different function depending on the type of encoder selected with Pr 3.38 and Pr 3.39.
Ab, Fd, Fr, Ab.Servo, Fd.Servo, Fr.Servo, SC
It is sometimes desirable to mask off the most significant bits of the revolution counter with these types of encoders. This does not have to be done for
the drive to function correctly. If Pr 3.33 is zero the revolution counter (Pr 3.28) is held at zero. If Pr 3.33 has any other value it defines the maximum
number of the revolution counter before it is reset to zero. For example, if Pr 3.33 = 5, then Pr 3.28 counts up to 31 before being reset. If Pr 3.33 is
greater than 16, the number of turns bits is 16 and the Pr 3.28 counts up to 65535 before being reset.
SC.Hiper, SC.EnDat, SC.SSI and 03.39 = 1 or 2 (Rotary encoder)
Pr 3.33 must contain the number of bits in the comms message used to give the multi-turn information. For a single turn comms encoder, Pr 3.33
must be set to zero. As well as setting the number of comms turns bits this parameter also sets up a mask on the turns displayed in Pr 3.28 as
described above. With SC.Hiper or SC.EnDat encoders it is possible for this parameter to be obtained automatically from the encoder (see Pr 3.41).
If Pr 3.33 is greater than 16 the number of turns bits is 16.
SC.Hiper, SC.EnDat, SC.SSI and 03.39 = 0 (Linear encoder)
When a linear encoder is selected no mask is placed on the turns information displayed in Pr 3.28, and so this parameter always displays the turns
information as a full 16 bit value with a maximum of 65535. Linear SINCOS encoders with comms are normally specified with a length for each sine
wave period and the length for the least significant bit of the position in the comms message. Pr 3.33 should be set up with the ratio between these
two lengths so that the drive can determine the drive encoder position during initialization. The Linear encoder comms to sine wave ratio is defined as
follows:
Linear encoder comms to sine wave ratio
With SC.Hiper or SC.EnDat encoders it is possible for this parameter to be obtained automatically from the encoder (see Pr 3.41). This ratio can be
greater than 255 for some EnDat encoders. If this is the case it is possible to use auto-configuration to set up the correct value provided the ratio is
less than or equal to 65535. The value cannot be stored in Pr 3.33 because it will be too large, and so Pr 3.33 is set to 255. Auto-configuration must
be enabled (Pr 3.41=1) and this setting must be saved, so that auto-configuration is carried out at power-up and each time the drive encoder is
initialized. Once auto-configuration has been carried out so that the internally stored value (not visible to the user) is larger than 255, this value cannot
be changed via Pr 3.33. The internal value can be reset to re-enable the function of Pr 3.33 by powering down and then powering up again, or by
auto-configuration with an alternative encoder where the corresponding value for Pr 3.33 is less than or equal to 255.
EnDat, SSI
Pr 3.33 must contain the number of bits in the comms message used to give the multi-turn information. If the encoder gives no turns information, for
example a single turn comms encoder, Pr 3.33 must be set to zero. As well as setting the number of comms turns bits that the drive will attempt to
obtain from the encoder, this parameter also sets up a mask on the turns displayed in Pr 3.28 as described above. With an EnDat encoder it is
possible for this parameter to be obtained automatically from the encoder (see Pr 3.41). If Pr 3.33 is greater than 16 the number of turns bit is 16.
It should be noted that some SSI encoders include leading zeros before the turns information. In this case the number of turns bits should include the
leading zeros.
Drive encoder lines per revolution
3.34
Bit SP
Coding
Range 0* to 50,000
Default 4,096
Update rate Background read (Only has any effect when the drive is disabled)
*Limited to a minimum of 1 except for Ab.Servo, Fd.Servo and Fr.Servo encoders.
When Ab, Fd, Fr, AbServo, Fd.Servo, Fr.Servo, SC, SC.Hiper, SC.EnDat or SC.SSI encoder are used the equivalent number of encoder lines per
revolution must be set-up correctly in Pr 3.34 to give the correct speed and position feedback. This is particularly important if the encoder is selected
for speed feedback with Pr 3.26.
Digitax ST Advanced User Guide
Issue Number: 1
Parameter
Parameter x.00
description format
FI DE Txt VM DP ND
=
Length representing the LS bit of the position in the comms message
FI DE Txt VM DP ND
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Advanced parameter Serial comms
descriptions protocol
RA NC NV PT US RW BU
1 1
Length for a sine wave period
RA NC NV PT US RW BU
1 1
Electronic
Performance
nameplate
PS
1
PS
1
Menu 3
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