The calibration of TDS-3 at a factory calibration solution of 1382 ppm (mg / l) based on NaCl is shown.
The video contains complete information on the calibration of TDS meters (in accordance with the requirements).
In the absence of a calibration solution, its "likeness" can be prepared by yourself. For this, it is necessary to have a pure NaCl salt (for example "Extra") and an accurate scale (preferably up to 0.001 g). The latter can be bought on aliexpress. Weigh the exact amount of salt (for example, 1 g, ie 1000 mg) and dissolve in 999 ml of distilled water. And on this solution check the instruments!
For reference (about existing calibration solutions):
Potassium chloride (KCl) is generally accepted for the calibration of conductivity meters. The instruments are calibrated to a value of 1413 μSim / cm at 25 deg. C. The conversion factor from μSim / cm in mg / l according to KCl is (usually) 0.5 - 0.57.
Solution 442 creates some imitation of natural water properties (water of rivers, lakes, wells, etc.) with a combination of 40% sodium bicarbonate, 40% sodium sulfate and 20% chloride. The conversion factor 442 usually ranges from 0.65 to 0.85.
Sodium chloride (NaCl) is used for water in which NaCl ions predominate or whose properties are similar to NaCl (marine and other saline and brackish waters). The conversion factor for NaCl (usually) is 0.47-0.5.
WHY DISTILLED WATER IS UNACCEPTABLE ?!
In the case of calibration with distilled water, we will only calibrate ("adjust") the very beginning of the measuring range (the calibration range will be very narrow, even considering that these cheap devices can be calibrated in increments of 0.1 to 1 ppm (depending on the model )).
2. Water for injection does correspond to distilled water (GOST 6709-72), HOWEVER it is manufactured according to FS.2.2.0019.15 Water for injection (pharmacopoeia.r... -inektsij /). After reading the information on the link, you can see the spread of conductivity under different conditions (in particular, at different temperatures).
3. I also met on my personal experience distilled water that is prepared in pharmacies (used for preparation of medicines and which can be bought) of different conductivity (even 3-6 μS / cm, these are, rather, exceptions). However, water for inectivities also has a spread of parameters; accordingly, we can not be sure that it is of "concrete" conductivity (this, of course, is not of significant importance for medical use). CORRESPONDENTLY, when calibrating the instrument with this water, accuracy can not be guaranteed, especially considering that only the beginning of the measuring range is calibrated !!!
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