Name: Emerson unidrive sp
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Menu 12

Unidrive SP Advanced User Guide 223

Issue Number: 10 www.controltechniques.com

Sectional control

The sectional control function is intended to apply scaling and a speed offset to a 16 bit position value to generate a new 16 bit position value. The

output can be used as an input to the position controller (menu 13) or to generate an encoder simulation output via the SM-Universal encoder plus

module. This function can be selected for either variable selector, but the description below relates to variable selector 1.

The position input can be derived from any parameter, however it is intended to be used with a position value that has a range from 0 to 65535. The

input is scaled so that as Pr 12.13 is varied between -4.000 and 4.000, the proportion of the input position change added to the accumulator varies

from 0.000 to 2.000 (the change of position input value is added without scaling if Pr 12.13 is 0.000). The remainder from the scaling division is stored

and then added at the next sample to maintain an exact ratio between the position input and the position output, provided the speed input is zero. The

controller only takes the change of position from the input source parameter, and not the absolute value, so that when the controller is first made

active the output does not jump to the source position, but only moves with any changes of source position after that point in time.

The range of the output of the accumulator is 0.00% and 100.00%. Unlike other functions the value is not simply limited, but rolls under or over

respectively. Although the output destination can be any parameter it is intended to be used with a position value that has a range from 0 to 65535.

The speed input defines a speed offset with a resolution of 0.1rpm. Full scale of the source parameter corresponds to 1000.0rpm. Scaling may be

applied using Pr 12.14 to give a full scale value of 4000.0rpm. The speed input is added to the accumulator to move the output position forwards or

backwards with respect to the position input.

This sample time for this function is 4ms x number of menu 9 and 12 functions active. Extending the sample time does not cause any overflow errors

within the function, however, care must be taken to ensure that the input or output positions do not change by more than half a revolution within the

sample time, i.e for a sample time of 4ms the input or output speed should not exceed 7500rpm, for a sample time of 8ms the speed should not

exceed 3750rpm, etc. If the output of this function is to supply a reference to the position controller in menu 13 it must be the only user function in

menu 9 or 12 enabled. If another function is enabled the input to the position controller will only change every 8ms (i.e. every 2 samples of

the position controller) and the speed reference applied to the drive could be very noisy.

The diagram below shows how the variable selector in Sectional control mode can be used to provide a position reference for the drive and act as a

source for encoder simulation to give the position reference for the next drive in the system.

Mode value Action Result

0 Select input 1 output = input1

1 Select input 2 output = input2

2 Add output = input1 + input2

3 Subtract output = input1 - input 2

4 Multiply output = (input1 x input2) / 100.0

5 Divide output = (input1 x 100.0) / input2

6 Time constant output = input1 / ((control param)s + 1)