How to define s + 2, no denominator, in a transfer func block in simulink ??

[cigua]

hi to all, have this problem, matlab doesnot allow me to enter just s + 2 defining in the numerator os a transfer func block and leaving nothing or just 1 as denominator, anyway to overcome this? thanks in advance for any help

numerator coefficient = [1 2] , denominator coefficient = [0 1] doesnt work in transfer func block parameters screen

 

[xnuke]

s + 2 isn't a causal transfer function since there is no such thing as a pure derivative, i.e., the s term. You can either send a signal to both a derivative block and a gain of 2 in parallel with each other and then add the output of the two blocks, or you can add a denominator with a high frequency pole (i.e., add a low-pass filter to the derivative function) and normalize the gain, e.g., (as+2a)/(s+b), where b is a positive integer >> 2 and a is b/2. If you have need of the signal into the function to be a step signal, use the latter suggestion, or the derivative block may cause the output signal to blow up.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[cigua]

thank you xnuke