High Speed Data Capture

I'm wondering if someone could point me in the right direction here. I have a test fixture traveling at a speed between 10 and 40 mph that has a 36" metal fin on it which passes through an electric eye speed gate. The signal goes high (24vdc) and then low (0vdc) when the fin passes through. Our Micrologix 1400 cannot capture the data fast enough, or so I'm told, because of the scan times, (front end and back end). Is there an add on high speed module which could capture this time within 1ms, pass it to the AB 1400 to do the speed calc? One more thing, the high speed module would have to know to stop counting after the pulse goes low in order to disregard any rebound signals.
Thanks in advance.

Investigate the EII (Event Input Interrupt) which can process the high speed inputs on a rising or falling edge, interrupting the processing of the main program. It may be fast enough to process your input.

Would the EII (Event Input Interrupt) return control of the program within say 10ms tops after detecting the falling edge? Could it store that time in a buffer to do the MPH calculation at a point later in time when the event was over?

The interrupt instantly transferrs control to a seperate program file, which you designate in the EII Function File setup. That program file can do anything available in code.

You might also want to check the input filter for the actual input you are using.
The filter is in the project tree on I/O config. I think the default is 8ms.

This will be difficult to do. As Caveman said there are filters on the input and even if they are turned off the input circuitry may be still very slow let alone the time it takes to respond to an interrupt.

The right way to do this is to have a device that is FPGA ( field programmable gate array ) based that doesn't use software in the traditional sense. These devices can respond within a micro second easily so usually it is the opto couplers that slow the response down.

Mike_E_Mike, you really should specify the accuracy you need or what you are really trying to do.
At 40mph the fin is traveling .7 inches per millisecond so count on a .7 inch error for every millisecond of delay.

So what is controlling the moving this fin at 40 mph? If it is a motion controller I would look at it because it probably has FPGA based latches that will respond in a few 10s of microseconds.

I learned a long time ago that one should never rely on software interrupt to capture motion data. There is too much jitter.

just a side thought - along the same question of accuracey.
isi it possible to install a geared reduction unit and read the speed.
then simply multiply by the reduction ratio say 40:1 or similar