Hi Eric,
I agree 100%.
It is sad to see that safety standards have joined to the pool of double standards recently.
Guys, you’re straying into an area of politics/sociology that too many people treat like a religious conviction. Discussions like that are best left to other not specifically technical forums.
My post was merely meant to be a warning to be aware of the legal regime where you do business.
In my over 40 years in the business I’ve sadly seen too many small business people miscalculate the financial equations and end up with horrific consequences. Usually it was only of consequence to the businesses viability, but occasionally the fall out included their own personal property due to their not consulting their liability insurance provider. I think it’s safe to say, not many people are OK with losing their house over failure to consult an insurance agent about their coverage.
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Hello Eric,
This is a very interesting thread.
Please allow me to add a few thoughts.
Assuming we are dealing with a DC power supply, we typically find a capacitor that can store a significant amount of energy. Is your voltage divider part of the bleeder circuitry for this capacitor? If it is I would advise against disconnecting it. It’s better to waste a bit of power than to risk failure of the bleeder resistor. Failure of the disconnect circuit will leave the system charged risking physical harm to an unsuspecting technician.
On a related note, the bleeder resistor often provides a measure of voltage stabilization. This may or may not apply to the laser application. However, having a small to moderate resistor load relative to the primary load is often desirable.
One final thought is to watch out for Thévenin with regards to that voltage divider. The schematic in your opening post has a Thévenin resistance of approximately 1 MΩ. That is very high. We must prevent loading by the op am buffer.
If you will allow a bit of self-promotion, you may want to consider the video linked below. You may have already considered these things, but it may be interesting to our readers. The input impedance is high and there is a measure of protection. This material may or may not be suitable to your application.
We would greatly appreciate if you would share your solution to this problem. Your lessons learned would be valuable way to help others. Pictures of your designs are especially welcome.
Best Wishes,
APDahlen
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Hi APDahlen,
No, the circuit is stand-alone HV measurement of the C02 laser tube voltage. The voltage is DC only. The C02 laser tube runs fine by itself from the laser power supply and what I propose to do is add the HV circuit to measure this laser tube voltage. I also have a circuit with a 1 ohm shunt resistor and shunt amplifier with 100 gain to measure the 0-50mA current from the laser tube return. I have tested the current measurement circuit on my K40 laser and it works well.
I want to measure the high voltage and the current from the laser tube so that I can get the voltage, current and calculate power so I can precisely calibrate my laser controller and also to get the state of health of the laser tube and the laser power supply. The laser tube is considered a consumable and it is also beneficial to make sure the laser power supply is functioning correctly.
When the customer receives a laser controller board from me there are some complex steps to take to get the tube current from an analog current meter, then they have to assume or find out what the theoretical drive voltage is and then use a calculator to calculate three values to input into the software to “calibrate” the settings required to set the laser PWM high and low cutoffs to get a valid usable and accurate range. As you can see a “theoretical” high voltage isn’t considered ACCURATE and therefore I want to create this voltage sense circuit. I need a safe way to measure this high voltage. This is a requirement, not a nice to have.
I hate to say it there are not a lot of people who are tech-savvy and they probably cannot do the complex steps above and that is why I want the circuits to measure and do all these things automatically behind the scenes. This means the customer installs this module and I tell them to run a command and it is done. Simple and accurate…
By the way, great video. Thank you for sharing 
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Some lasers require the bleeder resistor for stabilization, but some do not, and I believe these are integrated into the laser power supply or there are other means to control this. I know for my K40 it does not require one to operate.
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Hello ericn,
I wanted to say thank you for your quick and detailed responses on this thread. I can tell you are a passionate person, an educator, and a good writer.
If you have some time, I encourage you to answer a few questions on this forum.
Your expertise would be greatly appreciated by the readers.
Sincerely,
APDahlen