Page 106 - ExtendSim User Guide
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Areas of Application
The Clippers can be eliminated, but limiting the VCO input voltage to between 0 and +1 volt makes it easier to enter frequency modulation range parameters.
The Filter-Bandpass block (labeled Antenna tuner) is set to elliptical because of its economy (fewer poles & zeroes yield the fewest components). The Comparator block after the antenna acts as a limiter and detector of the FM signal. The Phase Locked Loop (PLL) block demodu- lates (separates) the input signal from the FM carrier signal. The output from the loop has a lot of pulses on it, so it is filtered slightly by a simple Butterworth filter. The low-pass filter after the PLL smooths out the switching transients always present in PLL outputs.
Because elliptical filters have very large group delays at their edges, a Chebyschev might be better. Try setting the noise to 1.0 volts and running the simulation with the elliptical filter. Then try setting the filter type to Butterworth, Chebyschev, click “Recalculate poles...” and rerun the simulation. The Chebyschev option works better than the elliptical filter, but notice how many poles are generated and how complex (costly) the filter will become.
The PLL's parameters can be easily changed for experimentation. For example, enter different bandwidths, damping, loop types, and phase comparators, and running the simulation again. Playing with the amount of noise on the signal can give interesting results. For example, increasing the amplitude in the Noise Generator block will quickly destroy the signal.
Finance, economics, inventory management, and marketplace competition all lend themselves to analysis through simulation. The following example explores how to minimize costs while still being able to provide products based on customer demand.
Inventory Management
A company holding inventory incurs both ordering costs and holding costs:
• Orderingcostsincludeorderprocessing,labortransportation,inspection,andsoforth.They are generally stated as a fixed cost per order.
• Holding cost includes such expenses as warehousing, insurance, taxes, obsolescence, and management. They are generally stated as an amount per item per time period or as a percent of unit cost per time period.
These costs are involved in a classic trade-off because as the number of orders per time period increases, ordering cost increases and holding cost decreases. The objective of inventory man- agement is to minimize the sum of the two costs.
☞ The Inventory Management model is located at \Examples\Continuous\Standard Block Mod- els. The model uses blocks from the Value and Plotter libraries.
Model assumptions
• Initiallythereare50unitsofinventoryonhand
• Demand is 10 units of product per week and increases to 12.5 units at week 4
• The lead time from stock order to stock delivery is 4 weeks for the first run
• SensitivityAnalysisautomaticallyvariestheleadtimebytwoweeksperrun,from4weeks on the first run to 10 weeks on the fourth run
• The stock-ordering pipeline is full at 10 units/week for the 4 weeks
• TheCorrectionFactoris1

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