Viewing Results for

Existing Controllers

2-6  Tutorial 2 - Modifying the Control Scheme Getting Started Guide

For each controller block, Aspen Dynamics has an associated

results table that displays the values of the process variable, set

point and output. To view the results table for controller LC1:

1. In the Process Flowsheet window, click controller block LC1

to select it.

2. Click the right mouse button and from the menu that appears,

point to Forms then click Results.

The results table appears:

3. Click the Close button to close the Results table.

Getting Started Guide Tutorial 2 - Modifying the Control Scheme  2-7

Adding a New Controller

You will now add a fourth controller, the MCHCOMP PID

controller. This controller will maintain the purity of MCH in the

liquid distillate product by manipulating the phenol solvent feed

flow rate of stream 2.

To add the controller block:

1. In the All Items pane of the Simulation Explorer, click the

expand (+) button next to Dynamics (the Dynamics library).

An expanded view of the Dynamics library is displayed.

2-8  Tutorial 2 - Modifying the Control Scheme Getting Started Guide

2. Click the Expand (+) button next to the ControlModels icon.

3. From the ControlModels list, click the PID object to select it.

4. Drag PID onto the Process Flowsheet window and drop it in a

suitable position above stream 2.

5. Click this newly-positioned block to select it.

6. Click with the right mouse button on the block and from the

menu that appears, click Rename Block.

7. In the Input dialog box, type the new controller name

MCHCOMP, then click OK.

Getting Started Guide Tutorial 2 - Modifying the Control Scheme  2-9

In this section, you will modify the control scheme to simulate a 5-

minute sensor dead time. This represents a delay in the

composition analysis.

To add the dead time block:

1. In the All Items pane of the Simulation Explorer, ensure that

the Dynamics library is in expanded view and the

ControlModels list is displayed.

2. Click Dead_time and drag it to the Process Flowsheet

window. Drop it to the left of the MCHCOMP PID block.

3. Click the newly-positioned block to select it.

4. Click with the right mouse button on the block and from the

menu that appears, click Rename Block.

5. In the dialog box that appears, type the name MCHCOMPDT

for the Dead_time block and click OK.

Your flowsheet looks like this:

Adding a Dead Time

Block

2-10  Tutorial 2 - Modifying the Control Scheme Getting Started Guide

Now you will specify the measured variable as the mole fraction of

MCH in the liquid distillate of column block B1.

1. If the ControlModels list is still expanded, in the All Items

pane of the Simulation Explorer, click the collapse (-) button

by ControlModels to collapse it.

2. In the Dynamics library, click Stream Types to display the

stream types in the Contents pane of the Simulation Explorer.

3. In the Contents pane of the Simulation Explorer, click and

hold down the mouse button on the ControlSignal icon and

drag it to the Process Flowsheet window. Continue holding

down the mouse button.

The ports that can be connected to this ControlSignal stream

type become highlighted with arrows. As you move the mouse

pointer over a port, the name of the port appears and an arrow

is highlighted to guide your selection.

Connecting the Measured Variable

Getting Started Guide Tutorial 2 - Modifying the Control Scheme  2-11

4. Move the mouse pointer over stream 3 and release the mouse

button on the port marked OutputSignal.

The Select the Control Variable dialog box for stream 3, the

liquid distillate stream, appears.

5. Click STREAMS("3").Zn("MCH") to select the liquid mole

fraction of MCH in the liquid distillate, then click OK.

In the Process Flowsheet window, the cursor becomes an arrow

connected to a solid black line.

6. On the MCHCOMPDT dead-time block, click the port

marked InputSignal.

Because there is only one input variable to connect to, the

control signal (blue broken lines) is automatically connected

to the dead-time block.

7. In the Contents pane of the Simulation Explorer, click and

hold down the mouse button on the Control Signal icon again

and drag it to the Process Flowsheet window.

8. Release the mouse button on the port marked OutputSignal of

the MCHCOMPDT dead-time block.

A control signal is automatically created and is ready to be

connected to a port.

2-12  Tutorial 2 - Modifying the Control Scheme Getting Started Guide

9. On the MCHCOMP block, click the port marked InputSignal

to connect the control signal.

The Select the Control Variable dialog box appears:

10. In the Select the Control Variable dialog box that appears,

click MCHCOMP.PV then click OK to connect the control

signal.

Your Process Flowsheet now looks like this:

Getting Started Guide Tutorial 2 - Modifying the Control Scheme  2-13

To specify the manipulated variable:

1. Ensure Stream Types is still selected in the Simulation

Explorer.

2. In the Contents pane of the Simulation Explorer, click and

hold down the mouse button on the ControlSignal icon.

3. Drag it onto the Process Flowsheet to the port marked

OutputSignal on the MCHCOMP block.

A control signal (black line with a cursor) is automatically

created and is ready to be connected to a port.

4. Move the pointer to stream 2 and click the InputSignal port.

The Select the Control Variable dialog box appears:

5. To select the phenol component mole flow of stream 2, click

the variable .STREAMS("2").FcR ("PHENOL").

6. Click OK to connect the controller output signal to the

manipulated variable.

Specifying the

Manipulated Variable

2-14  Tutorial 2 - Modifying the Control Scheme Getting Started Guide

Your Process Flowsheet window now looks like this:

You have finished connecting the MCHCOMP PID controller and

the MCHCOMPDT dead-time block. Now you can modify the

tuning properties for the controller blocks.

Modifying Controller Tuning

Properties

When you create new controllers, it is important to specify the

correct direction for the action. It is also important to check other

main properties such as gain, integral time, derivative time, bias,

and so on.

The following table shows the effects of direct or reverse action:

When the

action is

And the measured