The Electronic Units are mainly used together with transducers in order to protect lifting devices against overload, but can also be used in other applications, i.e., load indication, speed control, etc.

The signal from the transducer is processed by the printed circuit board of the electronic unit. The electronics have normally one PCB per hoist and one or more PCB's for summation. Each PCB has three switch functions controlling two relays.

Relay 1 is controlled by switch limit 1 set point, and is used as a warning signal, slack line switch or when engaging the micro drive of hoists with variable speed motors.

Relay 2 has two switch functions, 2A and 2B set points (delayed overload and instantaneous overload respectively) which controls the hoisting movement.

Switch limit 2A has a 0.5 sec delay before operating to allow for acceleration forces, whilst switch limit 2B = 2A + (0-25% x 2A) operates immediately in the event of a definite overload.

The PCB's have outputs for load indication instruments.

The Electronic Units are self-checking. Malfunction of the transducer amplifier or cable will indicate overload.

The Electronic Units are divided into two groups according to type of transducer used:

1. Transducers with amplifers giving an output signal of 4-20 mA. The current signal is resistant to interference and is therefore suited for long distances between the electronic unit and the transducer, and where noise interference is likely from high voltage sources.

2. Transducers giving a stablized signal of 0-approx. 5.5 mV/V. These transducers are suited for short distances between the electronic unit and the transducer and where less interference is likely. Please note that the stabilized signal at nominal capacity can vary from 0.6 mV/V to more than 2 mV/V.

For protection of individual hoists, electronic units of the types 9:100, 8:300 or 8:400 are recommended.

On cranes with more than one hoist and where the max. allowed load is less than the sum of the individual hoists, electronic units of the types 8:310 and 8:410 are used.

Electronic units are made for industrial use and can serve one or more transducers with individual and total surveillance, self-checking electronics with simple simulation of switch values and signal output for load indication.