Any thoughts about this would be appreciated!! I'm in the mist of a project in which thee specs have changed. basically I have a conveyor that feeds a pipe through two pre-heat coils into a furnace for heat treat. I have set up an aray of 12 sensors to detect pipe movement along the line. lets say that there are two groups of sensors. In the first group #1 is located before the entry, #2 is at the entry of the coils and #3,#4 are between each coil #5 is at the exit of the coils and #6 is mid ways between the last coil and the furnace. the goal is to detect a pipe hanging up entering the coils and furnace. To accomplish this I start a timer at each sensor and load the acc. at the next sensor. the distance between each sensor is known so I divide the distance by the time to get mm. per .o1 sec. and use that calc to determine the estimated time of travel to the next sensor. If the pipe is not there in that amount of time (I have a adder for error) then an alarm is set. I than add time to this value for a shutdown of the coil to prevent overheating of the pipe. After this was accomplished the end user decide we should monitor the trailing edge in case the pipe hangs up in the oven, thus the other 6 sensors. The idea in general is to move the time to travel each time so as the speed of the pipe changes so does the time needed between each sensor. OK thats a start not sure if I'm clear in my description so fire away if you have questions!! Thanks in advance!!