A negative input value for integrator gives a positive output

I have a simulink continuous integrator block with a lower limit output saturation at zero.

It takes a negative input and produces a positive output.

What am I missing here?

[Priyanshu Mishra]

Hi Maarten

Can you share your simulink file and elaborate your question so we can understand the model .

[maarten de Jong]

I could... But it is really a one-block-issue, as you can see from the inputs and outputs that are given in the question.

The time derivave of the quantity (dotN) is negative, yet the quantity itself (N_CH3OH) grows.

If you think you really need the entire model, I will gladly share it. However, it is quite large and I think matters will be needlesly complicated.

[stozaki]

Hello Maarten,

I thought the following :

N_CH3OH does not become less than "0" because the saturation lower limit setting value is 0.

If you set the saturation lower limit setting value to a negative value, you can obtain a negative value in N_CH3OH.

Regards,

stozaki

[Jonas]

@stozaki

The problem is not that N_CH30H does not go lower than zero really, the issue is more why it is RISING although the input is negative. I would expect that with a negative input, the output should just be saturated to zero.

Can you experiment with the saturation value? Does it work without the saturation to zero? What is you saturate to -eps for example?