EC – TDS General Information Sheet

INFORMATION FOR MILWAUKEE CONDUCTIVITY METERS

TDS Meter EC Meter
CF ppm ppt g/l uS/cm mS/cm
5 250 0.25 0.25 500 0.5
10 500 0.5 0.5 1000 1
14.1 706 0.76 0.76 1413 1.4
15 750 0.75 0.75 1500 1.5
16 800 0.8 0.8 1600 1.6
20 1000 1 1 2000 2
25 1250 1.25 1.25 2500 2.5
27.7 1385 1.38 1.38 2770 2.7
30 1500 1.5 1.5 3000 3
35 1750 1.75 1.75 3500 3.5
64.4 3220 3.22 3.22 6440 6.44
128.8 6440 6.44 6.44 12880 12.88
193.2 9660 9.66 9.66 19320 19.99

Milwaukee Conductivity Meters, Electrical Conductivity (EC) and Total Dissolved Solids (TDS) measure the ability of an aqueous solution to carry an electric current. It is measured with a small electrical current flowing between two probes set 1cm apart. The E.C. as it is known, flows faster when a greater amount of salts are in the solution. Microprocessor technology scales the measurement of electro conductivity into either microSiemens/cm (uS/cm) or milliSiemens/cm (mS/cm). Using inbuilt scaling the meters can also show in aqueous solutions levels as TDS in parts per million (ppm). TDS is the concentration of a solution as the total weight of dissolved solids. (1ppm = 1milligram/ltr). For Hydroponics, EC meters are favored over TDS by commercial growers, simply because they give the best estimate of the strength of a nutrient solution. TDS is a rough estimate while EC is exact. The total TDS is a mass estimate and is dependent upon the mix of nutrients as well as the concentration while EC is only dependent upon the concentration of nutrients.

When measuring a hydroponics solution in TDS it is recommended that the conversion formula TDS in ppm X .70 ( 442 Factor ) in stead of the usual .5 for aqueous solutions to obtain the equivalent EC reading.

To convert from uS/cm to mS/cm you divide by 1000 Example: 1,000 uS/cm = 1.00 mS/cm

EC meter display in uS/cm to convert to TDS –If your TDS meter is calibrated using 1382 ppm or 6.44 ppt then the conversion is (uS/cm x .50 factor) = (TDS) ppm

EC meter display in uS/cm to convert to TDS — If your TDS meter is calibrated using 1500 ppm then the conversion is ( uS/cm x .70 factor) = (TDS) ppm

Other examples:

2.00 mS/cm = 2000 uS/cm = 1000 ppm on .50 factor scale

2.00 mS/cm = 2000 uS/cm = 1400 ppm on the 442 scale or .70 factor scale

CONDUCTIVITY FACTOR CALIBRATION – microsiemens per centimeter (uS/cm) or millisiemens per centimeter (mS/cm). When using the Waterproof C66 conductivity meter in a nutrient solution after calibration, the Liquid Crystal Display (LCD) reading will be in mS/cm. A reading of 2.00 in the LCD is 2.00mS.cm or 2000uS/cm. It is worth noting that some articles in magazines and books mention EC values without specifying units. If the values are 1 to 5, it is mS/cm (dS/m has the same value) units. If the values are 10 to 50, it is in cF units. If the values are between 1000 to 5000 it is in uS/cm units.

TOTAL DISSOLVED SOLIDS – in parts per million (ppm) The total TDS is a mass estimate and is dependent upon the mix of nutrients as well as the concentration while EC is only dependent upon the concentration of nutrients. TDS meters are designed for sodium chloride (salt) solutions where the conversion factor is 1uS/cm = .5ppm. Because nutrient ions are on average much heavier than salt ions the true TDS is under estimated by 30% in a typical hydroponics solution. The conversion formula is only an approximation.

When choosing a TDS Milwaukee conductivity meter, select the TDS meter that is most suitable for your needs. The Waterproof T75 has a range of 0 – 1999ppm and the T76 has a range of 0 –9999ppm.

FAQ on EC/TDS Meters and Testers

Q. Should I store my EC/TDS meter in solution like I do my pH unit.

A. Do NOT store your EC/TDS meter in any type of solution. After use of a EC/TDS unit rinse in tap water or soapy water to neutralize the acidic fluid that was tested.

Q. Does the temperature of my EC/TDS test solution affect the reading.

A. Yes temperature has an affect on the reading unless you have an ATC unit. Almost all Milwaukee Instruments EC/TDS units are ATC ( Automatic Temperature Compensated )

Q. Do I have to calibrate before each use?

A. No, most units hold calibration very well. If you are using your unit every day then check it once a week. If you get a reading that is above or below what you were expecting then check the calibration at that point and retest your solution.

Q. There are many different brands of EC/TDS calibration solution to choose from, can I use one made from a company other than Milwaukee Instruments?

A. Yes and No: All manufacturers of meters and testers will tell you to use their specific calibration solution. That being said then Yes; most meter and tester manufacturers use the same calibration solution mix and quality control for there own meters so a 1382 for Milwaukee and 1382 for Oakton or Hanna are close enough to the same quality to be interchangeable. No, in that companies that DO NOT manufacture their own line of meters and testers do not understand and do not have the quality control necessary for production of the correct calibration solution As a manufacturer, the use of the wrong calibration solution by the public is one of our biggest problems.

Q. How do I know what calibration solution to use with my meter?

A. Please read the manual included with the meter.

Q. Can I reuse my EC/TDS calibration solution.

A. No, evaporation and contamination quickly change the mix.

Q. What are the symptoms of weak batteries?

A. For the end user to be assured that the readings are accurate and not worry about battery strength all Milwaukee Instruments units are designed to shut down when the batteries become too weak to give an accurate reading.

Milwaukee Instruments pH General Information Sheet

The pH value of a nutrient solution is a measure of the acidity or alkalinity of a solution. A basic, neutral solution is numerically equal to 7. The solution gets more acidic as the numbers decrease and more alkaline as the numbers increase. The ph scale ranges from 0 pH (very acidic) to 14 pH (highly alkaline). Pure water has a pH of 7, indicating that it is neither alkaline nor acidic, but neutral . Different nutrients are absorbed at different pH levels. Most plants need a pH level between 5.8 and 6.5 for optimum nutrient uptake. If the pH is too low, nutrients are bound up and the roots are unable to absorb them. If the pH is too high, your plants may succumb to toxic salt buildup, limiting the ability of the roots to intake water and food.

Your pH will fluctuate and should be monitored regularly. pH meters come in various degrees of sophistication and price. Some are handheld and need to be turned on each time they are used. They cost less but need more frequent calibration to keep them reading accurately. Other pH meters, such as the Milwaukee SMS115 & SMS110 are continuous reading models which are always on and should be mounted next to the reservoir.

FAQ on PH Meters and Testers

Q. Why is it important to keep my ph probe wet?

A. All ph probes use a cloth junction in the construction of the probe. This cloth is part of the diagnostic process in reading the ph. If the cloth becomes dry the unit will not be able to read.

Q. What is the difference between “Single Point” and “Two Point” calibration units in accuracy?

A. Single point is almost always done at the 7.0 position. Single point is fine as long as the area you are testing is within the neutral zone of 6.0 to 8.0 however 90% of everything we test in agriculture is acidic and for accuracy you need to have two point calibration. That is why most Milwaukee Instruments come with a 2 point calibration procedure and most of our units are provided with both 7.01 and 4.01 calibration solution.

Q. Why is it important to have a full range pH meter ( 0 to 14 ) when my test range is ( 4 to 10 ) ?

A. If a pH meter has a limited range such as 4 to 10 almost always the closer you get to the end of the range the less accurate your reading will be. Most of these limited range meters either can not be calibrated or are single point calibrated at 7.0 & they are not as accurate as full range meters

Q. How much effect does temperature of the solution have on pH accuracy?

A. Most pH meters are set for a optimum temperature of 77 F and have very little degradation between 45 F and 85 F

Q. How long will my pH probe last?

A. All Milwaukee Instruments a warranted for 1 year and should last from 18 to 24 months if the probe is kept wet in the proper storage solution and kept clean

Q. How can I test the life left in my probe?

A. A simple test can be performed using Windex glass cleaner with ammonia and any type of soft drink The procedure is as follows: Turn your meter or tester on and place the probe in a soft drink which is acidic and the reading will be from 2.7 to 3.9 then go to the Windex with ammonia which is alkaline. Your dis play should move very quickly up the scale to 10.5 –

11.8 If the probe slowly moves up the scale then it is time to consider replacing it.

Q. Do I have to calibrate before each use?

A. No, most units hold calibration very well. If you are using your unit every day then check it once a week. If you get a reading that is above or below what you were expecting then check the calibration at that point and retest your solution.

Q. There are many different brands of pH calibration solution to choose from, can I use one made from a company other than Milwaukee Instruments?

A. Yes and No: All manufacturers of meters and testers will tell you to use their specific calibration solution. That being said then Yes; most meter and tester manufacturers use the same calibration solution mix and quality control for there own meters so a 7.01 or 4.01 for Milwaukee and a 7.01 or 4.01 for Oakton or Hanna are close enough to the same quality to be interchangeable. No, in that companies that DO NOT manufacture their o wn line of meters and testers do not understand and do not have the quality control necessary for production of the correct calibration solution As a manufacturer, the use of the wrong calibration solution by the public is one of our biggest problems.

Q. How do I know what calibration solution to use with my meter?

A. Read the instruction manual included with the meter.

Q. Can I reuse my pH calibration solution.

A. No, evaporation and contamination quickly change the mix.

Q. What are the symptoms of weak batteries?

A. For the end user to be assured that the readings are accurate and not worry about battery strength all Milwaukee Instruments units are designed to shut down when the batteries become too weak to give an accurate reading.

Q. My pH meter has a little mould or dirt on the white strip and bulb will that affect the performance?

A. Yes, you can clean the probe in Isopropyl Alcohol ( rubbing alcohol ): Put the probe in full strength for 10 min. stirring gently then rinse well in tap water and let sit in Bottle Drinking Water ( RO water ) for 2 hours and then recalibrate.