Want up-down counter with display for industrial application reqd. to operate a safety device with reliability

Question

The reqmt. is for heavy duty crane in a steel plant.The hoists in a carne are eqquiped with limit switches to cut-off the motion at a preset height.This is a safety reqmt. since, if the hoist moves up uncontrolled with a load(in our case liquid metal) it will go to the top most point and the wire rope will break eventually. Thus reliability of the system has to be utmost.
We want supplier who can takup design and supply of an up-down counter based on the inputs from a proximity switch placed near the wire rope drum on top of crane and forward/backward pulses from the electric motor. The counter will be reqd. to give an output to trip the motor when a preset count is arrived.
The initial reqmt. is 30/35 nos after trial and approval of initial piece.But there is every chance of increased order once the product becomes succesful.

Answer 1

An Allen Bradley SLC 500 with combination digital Input Output card will do it with no problem. It has the Count Up (CTU) function that will count the various Input(s) and will trigger a done (DN) bit when the count value(s) become true. This setup will cost less than $900 and an additional 800 to 1200 for Panel View Display. You may want to investigate AB Pico Controllers which come equipped with text display this may be cheaper

Answer 2

Why use that when you could add a stepper motor to the drum reel and count rotations of the drum to know where your at on cable length. Then as an added safety, you can clip a flag to the cable to trip a limit switch.