Hello,
We use 5 SRF01 on an arduino 2560.
We had made a code like yours for to have the range of one sensor and it works well.
But we try since 3 weeks to have the range of the others.
Did you try to use more than one SRF01 on your arduino board?With single pin or each pin for each sensors?
Thank you for your help and sorry for our bad english, we are two swiss student.