Measuring Load Vltg of TRIAC using 89c52 and ADC

firing triac using variable voltages

hi,

I m currently working on project named, Butt Welding controller.... In this pro TRIAC (BTA41) is used to control the load voltage(AC)....

89c52 microcntroller is used to provid Variable voltage To fire the TRIAC.... Via DAC0808....

Now finally i want to disply the ACTUAL Load vltage on my display.

Here i m using ADC0804 to rread the load voltage.... Prior to ADC 230vAC to 0-9V DC transformer is used ... n then ATTENUATOR and Precision Rectfier (Using Op07) is uned ...

Now problen is .... the voltage i am getting at te output of Precisin rectifier is not Linear... Because i have tried my ATTENUATOR and Precision Rectfier circuit with ADC for a Variable AC Source.. it is working fine ... but it have problem in sensing LOAD voltage of TRIAC....

Does anybody gone through same kind of problem... Plz tel the Reason ... n if opssible Solution too.......

Thanks in Advance...

circuit dac0808 with 89s52

The way you try to measure voltages only applies if the input wave shape is sinus ..
Try to find an economical true AC-to-RMS converter and all troubles should vanish ..

Regards,
IanP