How to detect the 2nd falling crossing when it reaches the 2nd point. The signal will rise again after the 2nd crossing and then repeats.
Each time the signal falls at 20(2nd time) i want to capture it via relational block like the output signal in the image
Input Signal:
Model:
Output
There are multiple ways this could be done. One approach is to create a triggered counter, using a Triggered Subsystem, with the counter resetting itself if the count tries to go above 2.
An example of this is shown below. The trigger is generated by comparing your input to a constant (in this case 20) and incrementing the counter based on a rising edge of that trigger. Initialize the counter to 1, then either
increment the counter if the count value is currently less than 1.
reset the counter to 1 if the counter is already at 2.
In this example the counter resets every second crossing of the threshold.
If data typing is important this could also be done using logical/boolean values (i.e. True and False), rather than the 1 and 2 used in the example.
Using the answer above by Phil, i was able to create my version without using triggered subsystem
Sample answer
Related
I have two Matlab function blocks that one is producing zero signal for the other. I want to store the exact time that signal changes to one in another parameter in order to use it elsewhere.
How can I do it?
This type of functinality is achieved using a Triggered Subsystem, as per the image below,
The output of the trigger block will take on value of the input (which in this case is the simulation time) every time the trigger signal rises. Look at the parameters of the Trigger block inside the subsystem for other options such as falling edge, or both edge, triggering.
I want to remove a unwanted signal that occurs for 0.02sec. For example...i have a continuous signal with value 1. For a reason i become in some cases a signal with any value (+ or -) for max 0.02sec. After that I become again the value 1. Is it possible to remove this unwanted signal?
I will be very thankful for any help!
With best regards
You can debounce your signal using sample and hold as follows:
Every time a value change is detected in the input signal, start a counter and set the output to the original (pre-changed) input value for a number of cycles that you specify. After the waiting period is over, set the output value back to the input value. If the input remains at the new value after the wait period is over, then the output will assume the new value. Otherwise it will retain the original value after the input has settled to its original value and held it for the wait duration.
This can be modeled in Simulink with a combination of 'detect change' and 'switch' blocks.
Assume that you have a Simulink simulation where a certain signal is first positive and after some time t in a given interval, it becomes negative. Your goal is to find the zero-crossing.
A first approach would be to plot the signal over the given interval, save it and calculate the zero-crossing.
When repeating this simulation numerous times for varying parameters, it would be beneficial to be able to stop the simulation after the signal has become negative. Then there is already enough information for the calculation of the zero-crossing in Matlab. How could you do that?
Yes, use the Stop Simulation block with the appropriate logical input to the block:
You can use an if / else block to control the flow in the Simulink model. In the if / else block, you can choose the condition if u > 0, continue as normal if it's true, and use the else-option to bypass the rest of the flow you would otherwise run. For instance jump directly to the scope.
Another ways:
You can use Hit Crossing Block in Simulink to find time at the moment of hitting zero.
Another way - use any Trigger or Resettable system. It detects the zero crossing too. For example: this question at SO.
Of course you can also use User Defined function to detect zero crossing by your hand and do whatever you want with the signal at the same time.
About making a lot of simulations and then stops:
you can use Check Upper Static Bound for automatically stops simulation at the moment when zero will be crossed in nth time. For example:
I set upper bound = 10 for this block and this stops at 10th crossing.
There are a lot of ways to save function values in this points or just array of times but this is an another question :)
I have a matlab function block (which is not relevant) whose input is his previous output (loop). For example, if in a sample period the output is X, his input in the next sample period will be X, and so on.
This image shows a simplification of my simulation. I initialize the input of my function for the first loop.
The problem is that matlab functions recieves an event based signal from de initialization block in the first sample period (zero-duration), which I must convert to a timed based signal (so I can apply the unit delay that avoids an inifite loop, and allows to generate the next input as explained before). So, when I do so, I lose the information contained in the event-based signal (due to the zero-duration values) and the loop does not work.
If there was a way to intialize the loop in the time-based domain (green part of the image) so, in the first sample time, it is not a zero-duration signal, it would avoid the problem.
Is there any way to do so? Or, a different approach for this problem?
Two approaches come to mind
The initial condition can be set in the Unit Delay block, so it's not clear from your simplified example why you need the specific Initialization block.
You could just use a persistent variable inside the MATLAB Function block to maintain the state from one execution of the block to the next (noting that since it is event driven the block may not get called at every time step, only at each event triggger).
I'm using Matlab 7 and have a problem in creating a monoflop which shall raise for a specific time to "1" and after that time fall to "0". How can I do this with Matlab/Simulink 7?
I don't have any other version, so I can't use the "Monostable" Block from newer versions.
Any ideas?
greets, poeschlorn
There are a couple of ways to do this, depending on whether or not you want the pulse (i.e. "monoflop") to occur at a predetermined time or in response to another signal (like a rising edge)...
Creating a pulse at a predetermined time:
If you want to create a single pulse that steps from 0 to 1 at time tOnset, then steps back to 0 after a time tDur has elapsed, you can do this using a Step block, a Transport Delay block, and a Sum block. Here is what the layout would look like:
You would set the Step time of the Step block to tOnset, the Time delay of the Transport Delay block to tDur, and then subtract the delayed signal from the original signal.
Creating a pulse in response to a rising edge:
This is will be a bit more complicated. It will require two Detect Increase blocks, a Relay block, a Transport Delay block, a Gain block, and a Sum block. Here's what the layout would look like:
Assuming your input signal is either a 1 or a 0, the first Detect Increase block will output a 1 when the input steps from 0 to 1. By setting the Switch on point to 0.5 and the Switch off point to -0.5 for the Relay block, this will create hysteresis in the Relay such that the output will persist in the "on" state (i.e. an output of 1) after the brief pulse that occurs when the rising edge is detected.
To get the Relay block to switch back into the "off" state (i.e. an output of 0) after a specified time tDur, you would set the Time delay of the Transport Delay block to tDur. The Detect Increase block in the feedback loop will output a 1 when the delayed signal steps from 0 to 1, and this output will then be scaled by setting the Gain of the Gain block to 2.
When subtracted from the input signal, this gain will ensure that the output from the Sum block can be pulled below -0.5 no matter what the positive input is (0 or 1), thus ensuring that the Switch off point of the Relay block is reached and its output is turned off when the delayed signal has a rising edge (i.e. after tDur has elapsed). One result of this is that any additional rising edges occurring in the model input after the first rising edge and during the time tDur will be ignored. Once the output from the model returns to 0, the next rising edge on the model input will trigger another pulse.