resistance meter

[javari]

hi,
I want to ask that can we measure liquid resistance meter like ohm meter..I mean that ohm meter and liquid conductivity meter has a same logic..or are they different things
can you help me thanks

 

[javari]

hi,
I want to ask that can we measure liquid resistance meter like ohm meter..I mean that ohm meter and liquid conductivity meter has a same logic..or are they different things
can you help me thanks

 

[Leftyretro]

hi,
I want to ask that can we measure liquid resistance meter like ohm meter..I mean that ohm meter and liquid conductivity meter has a same logic..or are they different things
can you help me thanks

Same logic, however most will add a temperture element to the probe for compensation. I believe that normal units for resistivity in liquids is ohms/cm, at least that is a specification we have to test for when we are checking the deionized cooling water in a large variable speed drive system I support. The probe is just two wires spaced one cm apart and the we have to meet a spec of one megohm per cm or better. We use a omega conductivity meter that reads out in conductivity units or resistance units.

Here is the unit we use to measure out DI water resistivity:

**broken link removed**

 

[kchriste]

It really depends on the liquid. The problem usually is corrosion of the electrodes and the fact that the very act of measuring resistance puts current through the liquid you wish to measure.
If you are trying to measure the liquid level of say water in a plastic tank, then the capacitance meter method is much more reliable; you put two foil strips apx 5cm wide, close together, down the side of the tank and measure the capacitance between them to determine the liquid level.

 

[Sceadwian]

The ones we use at work are encased in thick plastic, they have small circular donut like nodes at the end, some kind of inductive meter, because the solutions we measure are very corrosive to metal. For some reason they measure in Siemens, which is just the reciprocal of resistance. I never figured out why they do that as it's like the difference between saying 1 megahertz and saying the time constant is 1 micro second. They should just use Ohms and be done with it.

 

[BeeBop]

the fact that the very act of measuring resistance puts current through the liquid you wish to measure.

And for this reason, you cannot use DC current to measure it. You need to use AC, around 10kHz, and above will work. A wien bridge oscillator can generate this...

For some reason they measure in Siemens, which is just the reciprocal of resistance. I never figured out why they do that as it's like the difference between saying 1 megahertz and saying the time constant is 1 micro second.

I guess since conductivity is the opposite of resistance. Siemens is mho/cm squared, or something like that. The interesting thing is ohm spelled backwards.

 

[Sceadwian]

It's not the opposite, it's the reciprocal. VERY big difference. It's as I said the difference between saying 1MHZ and 1 micro second peak to peak.
The term mho is an 'obsolete' according to Wikipedia.
Siemens == 1/Ohms

It's like saying "I have a 500 pico second time constant processor" instead of "I have a 2ghz processor" Why bother? It's just another 1/ you have to add to convert to modern resistance based equations.

 

[Roff]

Same logic, however most will add a temperture element to the probe for compensation. I believe that normal units for resistivity in liquids is ohms/cm, at least that is a specification we have to test for when we are checking the deionized cooling water in a large variable speed drive system I support. The probe is just two wires spaced one cm apart and the we have to meet a spec of one megohm per cm or better. We use a omega conductivity meter that reads out in conductivity units or resistance units.

Here is the unit we use to measure out DI water resistivity:

**broken link removed**

The unit of resistivity is ohm metres (or ohm cm, or ...), not ohms/cm.

 

[javari]

is there any circuit for resistance meter in liquid