Why using "Ideal Force Sensor" affects response of a Quarter Car Model?

Dear Community,

I'm trying to model a 2-DOF quarter car model using Simscape mechanics. I give a simple ramp function to the unsprung mass and collect the acceleration, velocity and position of the sprung mass without any problem. For verification of the Simscape model, I've made the same simulation by using classical "State Space Block" of the Simulink and got the identical results with the Simscape model.

But on Simscape model, when I used the "Ideal Force Sensor" to see the force between the sprung and unsprung masses (i.e, suspension force), response of the system (acceleration, velocity and position of the sprung mass) vibrated. The position of the sprung mass looks very familiar with the model which hasn't "Ideal Force Sensor", but has little fluctuations.

My question is: Why an " ideal " sensor on the model affects the output of a system?

.mdl files of the system with and without the "Ideal Force Sensor" are attached to the question. ("QuarterCar_Simscape.mdl" and "QuarterCar_Simscape_woForce_Sensor.mdl" respectively)

Thank you.

Best regards.

Halil Yahya Yeşilyurt

Answer 1

[Steve Miller]

Your force sensor is connected incorrectly. You need to connect the force sensor in series, not in parallel. Attached is the corrected model, which shows the system with and without the sensor giving the same answer.

--Steve

[Halil Yahya Yesilyurt]

Thank you very much, I'd also solved this question by simply reviewing the "Basic Principles of Modeling Physical Networks" topic in mathworks website which includes the descriptions and connections of sensor and source blocks, but totally forgot the question I asked to the community until an e-mail notification has come. Your answer will be helpful to starters, thank you again.