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| What is sampled-data system? |
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Definition
| system which has both discrete and continuous time signals |
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Term
| What does it mean by stable if system is open loop? |
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Definition
| transfer function has all poles in open left half plane |
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| what does it mean by stable if system is close loop? |
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Definition
| every possible closed-loop transfer function is stable |
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Definition
| yes, because the output is always bounded |
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Term
| why is it impossible to build a controller that's improper? |
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Definition
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Term
| what's the difference between stable and stablizing? |
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Definition
| stable is for when open loop, stablizing is for when closed loop |
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Term
| what does it mean by a function is linear? |
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Definition
| super position principal holds |
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Term
| what are steps of designing process? |
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Definition
1. Get the requirement
2. Model the plant (System identification)
3. Get transfer function for the plan
4. Design a controller
5. Simulate controller
6. implement the controller |
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Term
| what is system identification? |
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Definition
| given input and output, find model |
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Term
| what's the main difference between discrete time systems and continuous time systems? |
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Definition
| discrete time signal has a maximum frequency that can be exhibited, W <= 0.5 Ws |
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Term
| describe ADC by giving a system that has input and output. Draw the behavior of input and output |
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Definition
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| describe DAC by giving a system that has input and output. Draw the behavior of input and output. |
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Definition
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Term
| what's the condition for an ideal sampler? |
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Definition
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Term
| what's the condition for an ideal hold? |
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Definition
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Term
| in ece 481, what do we assume regarding S and H? |
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Definition
1. S and H are synchronized
2. sampling period is constant
3. no signal quantization |
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Term
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Definition
| yes, so they can be moved around |
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Term
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Definition
| no, they are not transfer functions because they are not time invariant |
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Term
| describe an SH and HS system. |
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Definition
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Term
| What are some causes of non-linearity? |
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Definition
1. on and off switch (relay)
2. saturator
3. static friction |
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Term
| What are some solutions to non-linearity? |
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Definition
1. cancel out the non-linearity
2. approximate by linearization
3. use limit cycles |
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Term
| Why does higher frequency mapped into lower frequency? |
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Definition
| because all signals can be decomposed into cos and sin which have property of higher frequency mapped to lower frequency |
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Term
| what are two ways to deal with aliasing? |
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Definition
1. sample really fast
2. use an anti-aliasing filter |
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Term
| what is a rule of thumb for cutoff frequency for AA filter? |
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Definition
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Term
| what are two disadvantage of sampling really fast to avoid aliasing? |
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Definition
1. noise might be also included
2. money issue |
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Term
| what are two disadvantage of using AA filter? |
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Definition
1. money issue
2. phase lag |
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Term
| what are three advantages to gain from fast sampling rate? |
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Definition
1. good at tracking and reject disturbances
2. sometimes you can only get good output by sampling fast
3. if AA is used, want cutoff for AA to be big, so sampling rate has to be big as well |
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Term
| what are rule of thumb when sampling using sampling really fast and when using AA filter? |
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Definition
1. sampling fast: 10Ws
2. AA: 25Ws |
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Term
| what are disadvantages to sample that fast? |
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Definition
| 1. economy 2. numerical issues |
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Term
| what are three ways to design controllers for sampled-data systems? |
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Definition
1. design by emulation
2. direct design
3. true sampled-data design |
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Term
| what are advantages of emulation? |
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Definition
| 1. easy because don't need to iterate designing C(s), only need to change sample frequency |
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Term
| what are disadvantages of emulation? |
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Definition
| economy issue (might not be able to sample that fast) |
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Term
| what are design steps in emulation? |
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Definition
| 1. find C(S) 2. find D[Z] by approximation 3. implement C[Z] |
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Term
| will emulation work for large T? |
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Definition
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Term
| What are design steps of designing in discrete time? |
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Definition
1. get Pd[z]
2. get C[z]
3. implement C[z] |
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Term
| What are advantages of doing direct design? |
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Definition
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Term
| what are disadvantages of doing direct design? |
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Definition
1. Sometimes final performance is not that good
2. inter-sample behavior is ignored
3. have to redo if T is changed |
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