Hi all,
I am working on a SPOT WELDING machine controller. I have been asked to modify the controller to modify some of the features. The welding machine controller is AT89S52 based system.

1. In our spot welding machines the welding current can be set initially and the job of welding controller is to keep this current constant even in case of power fluctuations. We use a thyristor for this purpose. In case of the power fluctuations the thyristor firing angle is adjusted accordingly to keep the welding current constant. In the existing design we use a Current transformer -> CA3140 -> ADC 0809 ->uC for measuring the current through the primary winding of welding transformer and in case the current flowing is altered due to power fluctuations than the thrystor firing angle is adjusted to bring the current to set value. In existing design we monitor the current through the primary of welding transformer which is of the order of 40-200Amp and assume that the actual welding current or the secondary current is in proportion to the primary and thus by keeping the primary current constant secondary current is also constant.

2. In the new modified design I have been asked to keep the welding current constant by actually manitoring the secondary current or the welding current. The secondary current is of the order of 30,000Amp to 100,000Amp. How to measure this so huge current and give the digital i/p to micro.

Please suggest me some Ideas.

Regards.
Prahlad Purohit