Redstone signals shortened by devices that output a shorter signal

I had a redstone wire running with a redstone torch putting the line at almost full strength where I was, I placed a weighted pressure plate down (Heavy) and put two light prssure plates on it.
I expected the redstone wire to stay the strength it was at (nearly full) when I activated the pressure plate by putting items on it.
What actually happened was the redstone signal that was near full strength was replaced by a much weaker signal that the pressure plate gave out.