Page 1 of 2HYSYS 3.0.1Transfer Function - Integrator-3.doc

Introduction:The Integrator option in the TransferFunction operation provides a special typeof ramping functionality, where the PVvalue is used to trigger ramping directionand rate but will not influence the final OPvalue.

Adding to the Flowsheet:The Integrator option is part of the TransferFunction operation.

Figure 1

Using the Integrator function:Setting up the Integrator Function is composed of thefollowing:1- Selecting the connections, on the Connections tab). The

PV signal is optional and a constant user-input PV canbe used in place of a connection.

2- Filling the PV and OP ranges (minimum and maximumvalues for the PV and OP), on the Parameters tabConfiguration page.

3- Specifying a PV value if a connection is not specified.Note that the PV value cannot be entered until the PVrange has been specified.

4- Check the Integrator option and specify the IntegratorPeriod (the default value is 10 minutes).

The behavior of the Integrator function is best describedthrough an example.

Example:An Integrator function is used to ramp the feed valve of athree-phase separator between fully closed and fully opened.The OP range is clearly the range of opening allowed by thecontrol valve, 0 to 100%. A user-input PV will be used inthis case, and we can select any PV range we desire. For

simplicity we will use a PV range of 0 to 100 too. In the “Q& A” section below we will discuss the usage of differentranges for the PV and OP and how it affects the outputsignal.The PFD below represents the model used:Figure 2

The setup on the Configuration page is shown below:Figure 3

So how does it work?The description below is not how the calculations are doneinternally within HYSYS, but is just a way to clarify whatthe function does.1- A “PVerror” is evaluated as follows:

PVerror = (PV – PVmin) / (PVmax – PVmin)

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Page 2 of 2HYSYS 3.0.1Transfer Function - Integrator-3.doc

How HYSYS Works is a series of short documents intended to shed light on specific tasks and operations in HYSYS and howthey work. These documents are offered free of charge to our clients courtesy of our Worldwide Technical Support team.

2- A “∆OP/time” is then calculated as follows:∆OP/time = PVerror * OPrange / T (time)where T = Integrator Period

3- The OP is then evaluated as follows:OP = OPold + ∆OP/time

4- The OP is then checked against the OP range as follows:If OP > OPmax Then OP = OPmaxIf OP< OPmin Then OP = OPmin

So how does this apply to our example above?Let us consider the following scenarios (using the rangesshown in the above):Scenario 1:Integrator Period = 10 MinutesInitial OP = 0PV set to 50%PVerror = (50 – 0) / 100 = 0.5∆OP/minute = 0.5 * 100 / 10 = 5OP will be ramped from 0 to 100 using a ramp rate of 5%per minute. It will take 20 minutes to reach 100%.

Scenario 2:Integrator Period = 10 MinutesInitial OP = 0PV set to 5%PVerror = (5 – 0) / 100 = 0.05∆OP/minute = 0.05 * 100 / 10 = 0.5OP will be ramped from 0 to 100 using a ramp rate of 0.5%per minute. It will take 200 minutes to reach 100%.

Scenario 3:Integrator Period = 10 MinutesInitial OP = 100PV set to -100%PVerror = (-100 – 0) / 100 = -1∆OP/minute = -1 * 100 / 10 = -10OP will be ramped down from 100 to 0 using a ramp rate of10% per minute. It will take 10 minutes to reach 0%.

Questions and Answers:1- HYSYS wouldn’t accept a PV value outside the PV

range, Why?The transfer function has an option to limit the PVvalues to only those within the PV range. If you uncheckthis option (found on the Parameters tab Configurationpage) you will be able to change the PV value to anyvalue you want. Note that cases read from older versionsof HYSYS (2.x) will have this option checked bydefault. For cases created in HYSYS 3.0.1 or later thisoption is unchecked by default.

2- Can I use a PV that is larger than the PV maximum?Yes. It will just make your “PVerror” term bigger andwill ramp the OP faster.

3- To ramp down, should I always use a negative PVvalue?To ramp-down use a PV that is less than the PVminimum. Any value will work, as it will make thePVerror term negative. For example if the PV range was50 to 100, a PV of 40 will result in the following:PVerror = (40 – 50) / (100 – 50) = -0.2, which willresult in a negative ∆OP (ramping down).

4- What happens when the PV = PV minimum?When PV = PV minimum the PVerror = 0 and noramping occurs.

5- What happens when the PV = PV maximum?When PV = PV maximum the PVerror = 1 and theramping time becomes equal to the Integrator Period.

6- Can I use the Integrator with other transferfunctions?Yes. Any of the functions can be combined.