Control Techniques Digitax ST Advanced User's Manual page 72

Parameter
Menu 4
structure
4.10 Torque offset select
Bit SP
Coding
1
Default 0
Update rate 4ms read
The torque offset is added to the torque reference when Pr 4.10 is one. The torque offset is updated every 4ms when connected to an analog input,
and so Pr 4.08 should be used for fast updating if required.
4.11 Torque mode selector
Bit SP
Coding
Range 0 to 4
Default 0
Update rate 4ms read
When this parameter is set to 1, 2 or 3 the ramps are not active while the drive is in the run state. When the drive is taken out of the run state, but not
disabled, the appropriate stopping mode is used. It is recommended that coast stopping or stopping without ramps are used. However, if ramp stop
mode is used the ramp output is pre-loaded with the actual speed at the changeover point to avoid unwanted jumps in the speed reference.
0: Speed control mode
The torque demand is equal to the speed loop output.
1: Torque control
The torque demand is given by the sum of the torque reference and the torque offset, if enabled. The speed is not limited in any way, however, the
drive will trip at the overspeed threshold if runaway occurs.
2: Torque control with speed override
The output of the speed loop defines the torque demand, but is limited between 0 and the resultant torque reference (Pr 4.08 + Pr 4.09 (if
enabled)). The effect is to produce an operating area as shown below if the final speed demand and the resultant torque reference are both
positive. The speed controller will try and accelerate the machine to the final speed demand level with a torque demand defined by the resultant
torque reference. However, the speed cannot exceed the reference because the required torque would be negative, and so it would be clamped
to zero.
Current
Depending on the sign of the final speed demand and the resultant torque the four areas of operation shown below are possible.
+ final speed demand
+ resultant torque
+ final speed demand
-resultant torque
This mode of operation can be used where torque control is required, but the maximum speed must be limited by the drive.
3: Coiler/uncoiler mode
Positive final speed demand: a positive resultant torque will give torque control with a positive speed limit defined by the final speed demand.
A negative resultant torque will give torque control with a negative speed limit of -5rpm.
Negative final speed demand: a negative resultant torque will give torque control with a negative speed limit defined by the final speed demand.
A positive resultant torque will give torque control with a positive speed limit of +5rpm.
72
Keypad and
Parameter x.00
display
FI DE Txt VM DP ND
FI DE Txt VM DP ND
Pr 4.08 +
Pr 4.09 (if enabled)
Speed
Pr 3.01
- final speed demand
+ resultant torque
- final speed demand
- resultant torque
www.controltechniques.com
Parameter Advanced parameter
description format descriptions
RA NC NV PT US RW BU
1 1
RA NC NV PT US RW BU
1 1
Serial comms Electronic
protocol nameplate
PS
PS
1
Digitax ST Advanced User Guide
Issue Number: 1
Performance