Adding Gas Discharge Tube to protect multimeter's input

[Willen]

Hi, I am using a $6 DT9205 multimeter from a decade, with Max 1000V DC input. Watching many videos on youtube is inspiring me to add some input over voltage protection. If I used a MOVs then the capacitance will be added to its capacitance measurement or something else. So I am thinking about a GDT, which have fairly low amount of capacitance. As a quick assume, I uploaded a picture of 9205 multimeter. Can I solder a couple of 1500V GDT across COM and two positive input wire, after there resistors, precisely indicated by red arrow in the image? If faced 1500V then maybe these resistor should be replace, blown by clamped GDT. (Shematic: https://obrazki.elektroda.pl/7393380900_1491737966.gif )

 

[Nigel Goodwin]

Why waste your time on a $6 meter?. Are you likely to ever do something so stupid as connect it to over 1500v?.

 

[JimB]

While a $6 DMM is a more valuable asset in Nepal than it is in the UK/Europe/USA, and your desire to safeguard that asset is well justified...
... I cannot help but think that the effort in protecting a $6 DMM is wasted.

If you are working on equipment which has 1500 volts, you need a better DMM.
Also, I doubt that GDTs applied as you suggest will be effective in protecting the sensitive parts of the DMM before damage occurs.
How will you test the modification to know whether it is effective or not?

JimB

 

[Willen]

Hi again, when I got this $6 DMM, I was a student and it was affordable to me. Currently any bluetooth model DMM is not arrived in Nepal. Nepal's biggest online shop Daraz has nothing about bluetooth DMM. It has been an year that we Nepalese can buy stuff from abroad. Now I am planing to buy a UNI-T's "UT60BT", an amazing $35 auto range bluetooth multimeter. It has amazing CAT III protection of maybe 5 PTCs and 3 MOVs as input protection inside. But more than $40 shipping charge to Nepal is terrific amount to me. Another Owon OW18E is also an amazing $50 bluetooth data logging multimeter in the international market. First problem is shipping again and 2nd one is this particular model has no input MOVs and maybe has just small two PTCs. So, in the future if I got an offer or lower shipping method and if I bought like a OW18E with no input protection, then my hope is to add some MOVs like UT60BT or some amazing Fluke has inside. Trying to learn something from the practice. I could use mosquito swatter high voltage generator and in my school, where I teach has an OWON oscilloscope, so I have a hope to see clamping waveform on my $6 DMM. I can experiment on it because it is pretty old, cheap and has less features than modern one.