Electronics > Beginners
How to set reference for a sine wave with dc supply
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Zero999:
Have you considered a current transformer?

A precision rectifier circuit and comparator could then be used to monitor the current and it has the added bonus of being able to adjust the threshold, rather it being fixed, as in the case of an opto-coupler.
C:
Hero999
This chain of posts is about changing from a foot switch to trigger spot weld to a contact sense trigger.

Think when it's all done, anishkgt will find that having spot weld contacts spring loaded and sensing pressure/displacement will do a better job.

Yes a current transformer could do sensing part, but first need current limited output to get contact sense with out doing spot weld.
anishkgt:
So i just checked the optocoupler with the input voltage from the secondary and they seem to be working. I was thinking of a low pass filter to cut off at 100Hz comprising of a resistor of 15.9k and a ceramic cap 0.1uf.

Can i use 5x1k and a 10k resistor all in series or should it be one 15k resistor ? About the TRIAC short pulse of 50ms Max should be ok as long as they are not continuous.

Attached schematic with a current sensor and a fuse.
C:

If the optocoupler  output is an input to a micro controller you can easily handle the pulses in software.

In addition with a little better software, you can get a better check as if it is not a series of pulses then something is wrong.

Resistors in series is same as total series resistance. With proper layout series resistors will allow higher voltage across the chain.

A TRIAC is for AC, Easy to turn on and stays on until less then holding current.
Not normal to try to turn off TRIAC.

 
anishkgt:
I have two things to decide on, should i go with a TRIAC or an SCR. TRIACs have lower current ratings than SCRs but conduct both ways unlike an SCR which only conduct one way.

If i were to go with SCRs i would need two in a back to back configuration.
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