Overload protection method

1. A method of generating an overload condition for an output module driving a load having a load current and a load voltage comprising the steps of:

monitoring the load current at sample intervals;

comparing the monitored load current to a predetermined load current threshold;

starting an overload timer in the event that the timer is not running and the monitored load current is greater than said load current threshold;

monitoring the load voltage at said sample intervals;

generating a ramped load voltage waveform for reference purposes in dependence upon an initial load voltage and a predetermined step size load voltage in the event that the overload timer is running;

generating the overload condition in the event that the monitored load voltage is less than said ramped load voltage reference waveform, the ramped load voltage is less than a predetermined positive ramp limit and the overload timer is running.

2. The method according to claim 1 , in which the predetermined step size is a function of an initial value of said monitored load voltage when said overload time is started.

3. The method according to claim 1 , further comprising the steps of:

setting a voltage max flag in the event that the ramped load voltage reaches a predetermined positive max voltage;

generating the overload condition in the event that the monitored load voltage is less than a predetermined negative ramp limit, the voltage max flag is set and overload timer is running.

4. The method according to claim 1 , further comprising the step of:

generating the overload condition in the event that the monitored load current is greater than said load current threshold and said timer exceeds a predetermined time limit.