Thank you, @WD0HHU. I have successfully used the Pade approximation now, and it works great.

I really appreciate the help you gave me to get over this hump.

I hope you had a great Thanksgiving yesterday.

@WD0HHU thanks again.  I'll give 4/4 a try later today and see what I can learn.

@WD0HHU Thanks for your help.  I had an issue downloading the Maple file, a 404 Server error, so I experimented with the two example functions you sent , but I didn't get great results.

I don't know much about the Pade Approximation so I didn't know how to choose the order of the numerator and the denominator.  I did some trial and error, but I was mostly guessing, so I didn't get very far.  Is there any guidance on the orders to best fit the delay?

Thanks, @Samir Khan ,for your reply.

Are there any plans to add support for delays to the Dynamic Systems package?

With everyone's help, I have managed to produce step responses, etc, by using the inttrans functions instead of the DynamicSystems functions.

Thanks @WD0HHU .

I've heard of it, but I have never used it. I would be interested in seeing how it is used and the benefits of it.

Thanks, @dharr for the insights on the convert(f,Heaviside).  That is very useful.  I also discovered the inverse convert(f, piecewise).

@C_R 

Thank you for your explanation.  I see what you mean. PhasePlot has just taken the opposite perspective since the phase always exceeds -180.  

As an experiment, I removed the doubling of the pole at zero and doubled the pole at two instead so that the phase ranged from -90 to -270.  This resulted in the range being what I expected, -90 to -270.

@Shaggy It looks like you've discovered some more interesting, but I would argue, undesirable behaviour.  Do you know what the mechanism is to raise it as an issue with Maplesoft?

@acer 

Wow, thank you for your help.  Your plot looks much better than mine!  I will give it a try.

@acer 

Thanks for your suggestion.

I tried that by using the MagnitudePlot and the PhasePlot funcions and then displaying the plots using the dualaxisplot.  While it did show both on one plot, it was pretty busy with the two curves overlying each other.  I'm not an expert in anything Maple, so can I ask if there is a way to separate the two plots vertically with dualaxisplot to mimic the output of BodePlot?

Do you know if Arrays of plots are supported in the plots:-display function in MapleFlow like it is in Maple?

@Kitonum 

Thanks for your help.

For my understanding, I would summarize the seq function support for units this way.

The seq function support units in the input parameters of a function and the return value but not in its iterand?

@Kitonum 

Thanks for that, but what if, for example, you have a function f(x), where x is expected to have units of length, and you have a problem where you want to mix metric and US Customary Units?

seq(f(x), x=1.0*Unit('m')..10.0*Unit('m'), 6.0*Unit('inch')), do you have to do the conversion yourself, seq(f(x*Unit('m')), x=1.0..10.0, 0.1524)?

@Thomas Richard 

On a related note, I thought I would use the modelica editor to create my component.  When I opened the Library Components->Thermal->FluidHeatFlow->Components, I discovered a few more components than in Maplesim: cylinder, OneWayValve and OpenTank.  Why aren't they available in MapleSim?

@Joe Riel Thanks for your help.