Control question

[steph]

Hi everyone my name is Steph, I'm a first year EE student. Just started control theory and I have been given a question on a heating system (water heater).

I have created a block diagram of the system and reduced it to a single transfer function. I have been asked to work out what the temperature of the water is when 2 volts is placed at the input. From the attached you will find i'm getting two different answers; 40 degrees C from the reduced block diagram, and 20 degrees C from the final transfer function. My head is telling me that the reduced block diagram is the correct answer (because the feed back voltage = input voltage). However because i have just started control theory i'm not 100% sure which will be the correct answer. If i'm thinking wrong could you please explain to me why.

Thanks Steph   

[Andy Watson]

Add voltage (or temperature) values to your block diagram. In particular, note the "error" voltage at the node between the summation and the forward-gain section (K=20).
Try it with output temperatures of 40 and 20 degrees - I think you will find that only the 20 degree senario gives consistent results.

[steph]

Hi Andy.

Thanks for that, I understand now