PLC dummy needs help picking a device

[thaukom]

Ok, any help would be great.
I am looking for a device to activate a speed warning sign for semi trucks. I have a device that has two 12V dc optocouplers that I need input from each to get a signal. One is a presence detector the other is a speed detector. One of the optocouplers will only give me a 1ms pulse.
I then need to control a relay (be nice if it was built in to the PLC) to give 120VAC to the flasher sign. I want to have the sign active for 7 seconds, so instead of a separate timing circuit I would like to have the PLC control the timing.
Also, to make it more fun it has to be a low temp device for minnesota weather.
Any thoughts on what device can do this.

 

[arkyny]

I would suggest buy a radar with analog output, then configure with your PC, make it simple

 

[rootboy]

Use those pneumatic hoses that you occasionally see on the highway. Have each of them connected to a pressure switch, and then set a bit in your PLC when the first hose gets crossed, and use that to start a timer. Reset it when the second hose gets crossed, and calculate your speed based on the amount of time it took to go from hose "A" to hose "B".

 

[Lancie1]

One of the optocouplers will only give me a 1ms pulse.

That is too fast for most PLCs, so if you have to use that optocoupler, you would need a pulse stetcher.

Also, to make it more fun it has to be a low temp device for minnesota weather.

Put the PLC and other electronics in an insulated heated cabinet, or indooors. You can run wires to the input and output terminals of a remote PLC (remote from the truck road).

 

[boneless]

Pick a PLC with integrated high speed counters. Being a Siemens user, I have used the 313C a lot for applications like these. 1 ms = 100 Hz is no problem. It is probably overkill for this application tho..