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Voltage and current measurement of TIG welding machine using data acquisition system

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Anujs

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Hi i have a TIG welding machine, i want to monitor its voltage and current during welding operation . i have a data acquisition system to do that but the problem comes when arc start using HF voltage circuit as it generates 3000V that damages the hardware used to measure voltage. please suggest any device using that i can isolate the voltage measurement circuit during HF operation.
 

To avoid 3000V HF, you can open the cover of the TIG welding machine and do the voltage measurement before the HF generation stage. I think it is easier.
 

Hi,

...or you make it 3000V proof.

Use HV resistors and a good clamping circuit.

Klaus
 

actually i need continuous measurement during welding process, so can not connect and disconnect manually. i have to use a method that can disconnect during HF spark only like relay.

can you please explain the circuit in detail
 

Can you explain the elaming and HV resistor circuit in detail
 

Hi,

The only value you give is "3000V". The rest is guessing.

Use high ohmic resistors that are rated for the 3000V.
A simple clamping circuit are two zeners in anti-series connection.

(Input) - R - (output) - zener - zener - Gnd.

*****

We don't know
* the voltage range of interest
* any timing specification of the 3000V pulse
* any timing specification of your signal of interest
* your aquisition system input voltage range
* any other specification


Klaus
 

Thanks sir,
i have all the information.
1. Voltage range of interest is:- 5VDC to 150VDC.
2. Timing specification of the 3000 V Pulse:- 2KHz, and duration is 100 ms.
3. Timing specification of your signal of interest: DC voltage and duration of measurement is 10 Min.
4. aquisition system input voltage range:- 0-150VDC
that is the information that i have.
 

actually i need continuous measurement during welding process, so can not connect and disconnect manually. i have to use a method that can disconnect during HF spark only like relay.

can you please explain the circuit in detail

Hi Anjus,
Relay is not a good idea, because it can not interrupt high voltage and it is slow.
The HF generation stage has a HF coil made of thick wire and few turns which is in series with the electrode (tungsten) cable. It's resistance is negligible and cause negligible voltage drop during welding. So if you measure the voltage before this coil you will get almost the same voltage which is across the arc. To get accurate result it is possible to subtract the voltage drops across the electrode cable and HF coil if you know the current. For continuous measurement, you connect wires at the specific terminals and bring the other terminals out of the machine and keep connected the data acquisition system there.
 

thanks for replying, i have sketch block diagram of the electrical connection as per my connection please check the attached circuit and reply correct solution. HF circuit is in parallel not in series so voltage will be same at all points. IMG_20160714_223529.jpg
 

I have attached two pictures below showing the HF circuit. You can see the secondary coil of HF transformer is connected in series with the electrode (negative) terminal. Your machine design may be different. If your sketch is correct then there must be an inductor which will block HF to enter into the DC power supply. This inductor will carry the welding current, so it must have several turns of thick wire on a ferrite core. You need to measure voltage before the position of it. First you need to find the inductor. If possible you can post a picture of the real connection.





- - - Updated - - -

Showing possible inductor location, I edited your picture and attached below.

 

Measuring the voltage outside the welder creates some interesting problems, because TIG welders have high voltage radio frequency ac (pilot arc) superimposed on the main high current dc.

To measure that requires high bandwidth, but the wideband noise from the arc is going to make nonsense out of anything you can monitor.

Kind of like asking how can I record a close intimate whispered conversation in the presence of a heavy metal rock band going full blast. Its not really possible.

Back inside the guts of the welder, the dc current can easily be monitored before the pilot arc rf is added, so its not a problem there.
 

Like any arc, the power conducted occurs at low voltage after the high voltage trigger.
Simply use a low pass filter and the fast transient RF will be filtered. Start with 100Hz LPF to monitor both V and I then multiply.

When I monitored 100kA diffusion welding below 6V back in the late 70's , I used shielded twisted pair at right angles to the weld current to a monitor. As the welded joint length increased around the tube, the tube conduction current had to be increased between inner and outer tubes being welded with a zirconium shim. Forced water cooling had to be regulated at the same time as current. I monitored current using a length of the massive copper arm calibrated for 50mV / per 100kA
 

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