I build a EC meter from RVS whire and program it for the arduino. But even when I put more salt in the solution the measerment dont change. I now that the programming is correct beceause I use it from a site for schools. Only I use 180 ohm resister inplace of a 100 ohm. How do you even now wich resister you can use in a project.
And what can the reason by that mine measerment dont change, even when I put more salt in it?
The mistake(s) could be in the code, the circuit or both.
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Hi @liekske76!
Welcome to the forum!
For sound support you should post information about
- relevant hardware and its wiring
- code (inside code tags!!)
- version of the development environment (e.g. Arduino IDE 2.3.10)
If you got the project from an external page where one can find a complete description you may link that page (though not everyone in the forum likes to follow external links ...).
In your specific case it this the project you mentioned?
https://www.hackster.io/HackingSTEM/hacking-stem-electroconductivity-meter-a82c58
To give you an example of the use of code tags (see the button <code> in the post editor menue!):
// This text is inside code tags!
// It provides keyword highlighting and can be easily copied.
// The window has a limited number of viewable lines and will show
// a vertical scrollbar if the sketch is longer
void setup(){
// Put your setup code here
}
void loop(){
// Put your main code here
}
If your code does not look like this, somethings wrong ... 
ec2021
That resistor change makes a big difference, I expect you are getting just high readings. The circuit is a simple resistor divider where the 100 Ohm is the lower resistor and your probe is the upper resistor. The A/D measures the voltage at the junction of the probe and resistor.
It's helpful when you start a post to add some information instead of "EC meter from RVS".
By all means use abbreviations further in the post, but Conductivity Meter (EC) would be clearer and RSV is anyone's guess. It would also help if you gave some information on your project, especially the medium you are hoping to use it with.
Have you checked readings in deionised water? Tap water can be several hundred microS/cm and seawater about 6-milliS/cm, so quite a range. Temperature is also important.
What's the output from your conductivity meter? If it has analogue, you could check with a multimeter, but if it's digital, you will have to decode it.
Two wires and a multimeter in resistance mode would give you an idea of what's going on when you change salt? concentration.
Without knowing which Arduino you are using I will assume you are using the Arduino UNO. That A/D has a range of 0 - 1023 (10-bit ADC) or 0x0 to 0x3FF. If you are seeing the higher number which I believe you are it cannot go any higher no matter how much salt you add. If it is reading 0 short the two pins and it should jump to 0x3FF.