Products > Test Equipment
New UNI-T UT892 2000V AC/DC High Voltage Multimeter
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Fungus:
Maybe there's an excess of cheap PTCs in Shenzhen right now, so ... use what you've got!  8)
Mechatrommer:
better cheap than nothing. no? where to get $40 2KV meter verified to 4KV (modded with 2x 0806 resistors) safe? ;D
joeqsmith:

--- Quote from: Mechatrommer on September 12, 2022, 06:52:17 am ---Its designed to go open, surge Resistor will go short.

--- End quote ---

Once the PTCs arc, they become a very low impedance.  Without anything to limit the current, the down stream protection will normally get damaged to where it goes open then it's everything after that.   While testing the meters, we have seen the resistors go open.   

The PTCs come into play (will start to heat)  when the low voltage clamps are active and you have applied a high enough voltage to the inputs for a long duration.  For example, you have the meter set to ohms and then proceed to plug the meter into your wall socket.   
Mechatrommer:

--- Quote from: joeqsmith on September 12, 2022, 12:39:42 pm ---
--- Quote from: Mechatrommer on September 12, 2022, 06:52:17 am ---Its designed to go open, surge Resistor will go short.
--- End quote ---
Once the PTCs arc, they become a very low impedance.
--- End quote ---
and this happens when we violate its physical law (distance between naked pins) and we cant blame the manufacturer really, if we test it beyond its recommended limit.
joeqsmith:

--- Quote from: Mechatrommer on September 12, 2022, 01:49:32 pm ---
--- Quote from: joeqsmith on September 12, 2022, 12:39:42 pm ---
--- Quote from: Mechatrommer on September 12, 2022, 06:52:17 am ---Its designed to go open, surge Resistor will go short.
--- End quote ---
Once the PTCs arc, they become a very low impedance.
--- End quote ---
and this happens when we violate its physical law (distance between naked pins) and we cant blame the manufacturer really, if we test it beyond its recommended limit.

--- End quote ---
If designers use a 100V part in a 10kV application, I most certainly will.   There is a reason that the higher class meters use the larger parts and further limit the current.  There also a reason I have never seen a PTC fail in the higher class of meters.   Nothing to do with this particular meters 2kV input. 
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