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TDS Meters

How do I care for my TDS meter?
Why do I experience different reading in the same water?
How can I get the best reading?
Doesn't your body need the minerals in drinking water?

 


HOW DO I CARE FOR MY TDS METER

1. Do not store meter in high temperature or in direct sunlight.

2. Do not drop or completely submerge the meter in water or dip beyond the maximum immersion level. (2") NOTE: The COM100 is water tight and can be completely submerged. Please ensure that the battery compartment for this meter and probe gasket ring are firmly tightened before submersing in water.

3. The batteries may need to be replaced after extended usage or life span.

4. When necessary, clean the electrodes by soaking the tip in an acid (e.g., vinegar or diluted hydrochloric acid (muriatic acid)) and then rinse well in water. If it is heavily fouled with organic material, soak the tip in alcohol or bleach. Gently wipe with a soft, nonabrasive cloth may also be acceptable.

5. After repeated use in high TDS water, it is advised to clean the electrodes to prevent residue build-up.

 

CALIBRATION

1. All meters come factory calibrated. HM Digital meters are calibrated at (342 PPM) and are ready to use. They are designed to stay consistent. However, after prolonged usage, it may help to re calibrate your meter using a commercial standard NaCI-based solution, which is approximately, 0.5 uS of conductivity.

NOTE: HM Digital products are calibrated with a 342 PPM NaCI solution. This is suitable for most applications. However, if you are measuring samples that are consistently over 1000 PPM, it is recommended to re calibrate the meter for that specific application. TDS meters are more accurate when calibrated at levels that are as close as possible to the sample being tested (such as hydroponics, aqua culture, tinting and dying or brackish water). The COM100 is factory calibrated with Potassium Chloride, which is 1413 micro-siemens solution (default mode is EC-KCI).

COM100 calibration solutions:
KCI - Potassium Chloride is the international standard to calibrate instruments that measure conductivity.
442 - Developed by the Myron L Company, 442 simulates the properties of natural water (rivers, lakes, wells, drinking water, etc.) with a combination of 40% Sodium Bicarbonate, 40% Sodium Sulfate and 20% Chloride.
NaCI - Sodium Chloride is used in water where the predominate ions are NaCI, or whose properties are similar to NaCI, such as seawater and brackish water.
EC (uS) - Measurements in EC (uS) do not have conversion factors, but do require the correct setting for the proper temperature coefficient.

2. Immerse the meter into the calibration solution. If the meter does not read within 2% of the calibration solution, adjust the reading by inserting a mini screwdriver into the trimmer pot (the hole on the back of the meter). Turn the trimmer clockwise to increase the reading and counterclockwise to decrease the reading. NOTE: that the adjuster is very sensitive.

 

WHY ARE THERE DIFFERENT READINGS IN THE SAME WATER WITH THE SAME METER?

IONS:
The nature of charged positive ions (which is what the TDS meters are measuring) is that they are always moving. Therefore, there may always be variations in the conductivity, and thus a different reading.

TEMPERATURE:
A tenth of a degree change in temperature may increase or decrease the conductivity. Additionally, the temperature coefficient (what the reading is multiplied by to adjust for temperature differences) changes slightly depending upon the range of PPM. Virtually every meter under $500 has a single temperature coefficient, regardless of the range. ( The COM-100 offers three temperature coefficient options, but each is linear once selected).

AIR BUBBLES:
Tiny air bubbles that have adhered to a probe could potentially affect the meter reading.

LINGERING ELECTRICAL CHARGES:
Electrical charges off fingers, static electricity off clothes, etc. on the meter and lingering electrical charges in the water will affect the meter reading.

BEAKER / CUP MATERIAL:
A plastic cup can retain lingering electrical charges more than a glass can. If the meter touches the side of the glass or plastic, it could pick up a slight charge. If the container is retaining a charge, it could affect the meters reading.

VOLUME CHANGES:
Different volumes of the same water may have different levels of conductivity, which will affect the meters reading. Displacement may also affect the reading as well.

PROBE POSITIONING:
The depth and position of the probe in the water sample may affect the meter reading. For example, if a meter is dipped into the water, removed and then dipped into the water again, but in a different spot, the reading may change.

 

HOW CAN I GET THE BEST READING

SHAKE:
Always make sure to shake excess water off the probe before dipping it into a water sample, even if it's the same water.

STIR / TAP:
After dipping probe in the water, always lightly tap it against the side and stir the meter to remove any lingering air bubbles.

POSITIONING:
When taking the reading, always make sure to hold the meter straight up without it touching the sides or bottom of the glass/beaker/cup. The probes should be suspended as close to the center of the water sample as possible. In-line meter probes need to be positioned in the tee so that the water will flow between the two metal prongs, not against them.

TIME:
The longer the probe is in the water, the more accurate the reading will be.

TEMPERATURE:
25 degrees celsius is the ideal temperature for meter readings, even if the meter has ATC.

RINSE:
If switching between very low and very high PPM water, always rinse the probes with distilled water to avoid any build-up.