The "Anti Two-Block"system, from now on described as A2B, generally splits up in three systems theorys. I will describe each separately.
1. 24V, NC Feedback.
This system is not used a lot, but you will find it on some cranes, ex- Liebherr LTM 1400 +++. Safety evaluation of this A2B system is rather high, and the only possibility for error that will generate a element of risk, is a sneak current on to the wire for the feedback signal.
2. 24V, NC To 0V.
This system is often used on Japanese cranes. Safety evaluation of this A2B system is dependent on the condition of the wiring and reel, and the possibility for error that will generate a element of risk, is any short circuit between the output wire and crane body.
3. Adjusted voltage/current, NC in serial with resistor.
This system is very safe, and the only possibility for error that will generate a element of risk, is any error in the A2B switch. The resistor must be in the switch, or very near it, and any short circuit, sneak current or bad connection, will stopp the winsh. PAT, Ettlingen, Germany, uses this system.
For more details, please contact Skailand Kranservice at www.mobilcrane.com