JohnnyPotSeed1969
Well-Known Member
Here is some information about nutrient strength. It's an in depth explanation of measuring TDS & EC and exactly what that means to you as a grower.
[FONT="]Know your Conductivity meter[/FONT]
[FONT="]Measuring Nutrient Strength[/FONT]
[FONT="]TPS Conductivity and TDS meters measure the ability of an aqueous solution to carry an electric current. It does this by measuring the electric current between two electrodes (the electricity flows by ion transport). A nutrient-rich solution will have a higher conductivity than a solution with less ionic salts (nutrients). The higher the nutrient level the higher is the conductivity.[/FONT]
[FONT="]Microprocessor technology scales the Conductivity measurement into either milliSiemens/cm (mS/cm) or microSiemens/cm (uS/cm). Using a mathematical formula, the meters are also able to show the nutrient levels as TDS in parts per million (ppM) or parts per Thousand (ppK). TDS is the concentration of a solution as the total weight of dissolved solids. (1 ppM = 1 milligram/litre and 1 ppK = 1 gram/litre).[/FONT]
[FONT="]Conductivity meters are favoured 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 Conductivity is exact. The total TDS is a mass estimate and is dependent upon the mix of nutrients as well as the concentration while Conductivity is only dependent upon the concentration of nutrients.[/FONT]
[FONT="]The true ppM conversion factor is complicated by factors, including the type of ionic salts present in a nutrient solution, their concentration, and the temperature of the solution.[/FONT]
[FONT="]Our meters are capable of compensating for temperature. No meters have ability to distinguish between different types of ionic salts. Conductivity measurements are also complicated by the fact that not all salts conduct an electric current equally. Ammonium sulphate conducts twice as much electricity as calcium nitrate, and more than three times that of magnesium sulphate (Resh, 1989). Also, nitrate ions do not produce as close a relationship with conductivity as do potassium ions (Alt, D. 1980). Consequently, the higher the nitrogen to potassium ratio in a nutrient solution, the lower the conductivity values.[/FONT]
[FONT="]Millimho and micromho are commonly used by hydroponicists in North America and in earlier scientific literature. The basis for this unit came from the ohm, which is the unit used to measure electrical 'resistance'. A 1 ohm resistance with 1 Volt across it will conduct 1 Ampere of electrical current. The electrical equation is V (volts) = I (ampere) * (times) R (resistance) where R is measured in ohms. The reciprocal of resistance is 'conductance', with the mho (ohm spelt backwards) used to describe conductance.[/FONT]
[FONT="]The scientific literature adopted Millimho per centimetre (mmho/cm) and micromho per centimetre (mmho/cm), where 1mmho/cm = 1000 mmho/cm.[/FONT]
[FONT="]The metric equivalent for mho is Siemens, where 1mho/cm = 1mS/cm = 1000uS/cm. The metric system is used extensively throughout Europe, South Africa, Australia and New Zealand.[/FONT]
[FONT="]For hydroponics, scientific literature generally uses deciSiemens per metre (dS/m) to measure conductivity, with milliSiemens/cm (mS/cm) and microSiemens/cm (S/cm) the established and accepted units of measurement for soilless culture, where 1dS/m = 1mS/cm = 1000uS/cm as measured by a Conductivity meter.[/FONT]
[FONT="]An old unit of measurement is cF (Conductivity Factor). These meters use a scale of 0 to 100, where 0 represents pure water (zero ionic salts). cF is not a recognised scientific measurement, and it has as its basis 1mS/cm = 10cF. cF measurements were first introduced in the United Kingdom during the early development of NFT (Nutrient Flow Technique).[/FONT]
[FONT="]Calibration Solutions[/FONT]
[FONT="]For hydroponics applications there are two requirements. The calibration solution should represents a value close to the expected conductivity of a nutrient solution. The solution should use the same or similar types of ionic salts known to be in the nutrient solution.[/FONT]
[FONT="]The calibration solution most suitable for hydroponics applications is the KCl (potassium chloride) Standard. Standard values used in hydroponics applications are 2760 uS/cm or 1413 uS/cm at 25 OC. TDS standards are also available from TPS. [/FONT]
[FONT="]When to Calibrate[/FONT]
[FONT="]Meters should be calibrated when first used, and then regularly thereafter. Whilst conductivity sensors are generally very stable long term, a regular calibration check will ensure your system is operating correctly. [/FONT]
[FONT="]Checking the calibration should be a routine that uses a fresh calibration solution. The recommended shelf-life for a factory sealed calibration solution is 1 year. Do not mix used calibration solution with new solution. Once the meter has been tested and/or calibrated, the solution should be discarded; not returned to the reagent bottle.[/FONT]
[FONT="]Remember - the accuracy of your measurements can determine the success or failure of your crop. Regular calibration checks in accurate standards may avert disaster ![/FONT]
[FONT="]The Importance of Temperature Compensation[/FONT]
[FONT="]Conductivity requires mobile ions in solution, when the mobility rises because of increases in temperature the conductivity measured also rises. For every 1OC temperature change, the conductivity of a nutrient solution will increase by around 2% (Resh, H.M., 1991). This temperature coefficient varies with the type of salts in the solution, the concentration of those salts and the temperature itself.[/FONT]
[FONT="]When calibrating meters, the calibration solution temperature should be as close as possible to the nutrient solution to be tested, to minimise temperature effected errors.[/FONT]
[FONT="]TPS conductivity meters have an Automatic Temperature Compensation (ATC) feature, which scale the readings to a standard temperature of 25OC. When the temperature deviates from 25OC, then the meter automatically compensates for temperature changes experienced in the nutrient solution.[/FONT]
[FONT="]Meter Ranges[/FONT]
[FONT="]TDS meters suitable for soilless culture should have a range from 0 to 10,000ppM, and Conductivity meters from 0 to 20mS/cm (20,000uS/cm).[/FONT]
[FONT="]TPS manufactures the multi-range, hand-held Aqua-C and WP-84 for agricultural applications. Models that also incorporate a pH readout are the Aqua-CP (single Conductivity range) and WP-81. They also manufacture the purpose-designed hydroCHEM-DS Conductivity and pH dosing controller for hydroponic applications. This unit continuously monitors Conductivity and pH and maintains user-set levels using inbuilt peristaltic dosing pumps.[/FONT]
[FONT="]Know your Conductivity meter[/FONT]
[FONT="]Measuring Nutrient Strength[/FONT]
[FONT="]TPS Conductivity and TDS meters measure the ability of an aqueous solution to carry an electric current. It does this by measuring the electric current between two electrodes (the electricity flows by ion transport). A nutrient-rich solution will have a higher conductivity than a solution with less ionic salts (nutrients). The higher the nutrient level the higher is the conductivity.[/FONT]
[FONT="]Microprocessor technology scales the Conductivity measurement into either milliSiemens/cm (mS/cm) or microSiemens/cm (uS/cm). Using a mathematical formula, the meters are also able to show the nutrient levels as TDS in parts per million (ppM) or parts per Thousand (ppK). TDS is the concentration of a solution as the total weight of dissolved solids. (1 ppM = 1 milligram/litre and 1 ppK = 1 gram/litre).[/FONT]
[FONT="]Conductivity meters are favoured 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 Conductivity is exact. The total TDS is a mass estimate and is dependent upon the mix of nutrients as well as the concentration while Conductivity is only dependent upon the concentration of nutrients.[/FONT]
[FONT="]The true ppM conversion factor is complicated by factors, including the type of ionic salts present in a nutrient solution, their concentration, and the temperature of the solution.[/FONT]
[FONT="]Our meters are capable of compensating for temperature. No meters have ability to distinguish between different types of ionic salts. Conductivity measurements are also complicated by the fact that not all salts conduct an electric current equally. Ammonium sulphate conducts twice as much electricity as calcium nitrate, and more than three times that of magnesium sulphate (Resh, 1989). Also, nitrate ions do not produce as close a relationship with conductivity as do potassium ions (Alt, D. 1980). Consequently, the higher the nitrogen to potassium ratio in a nutrient solution, the lower the conductivity values.[/FONT]
[FONT="]Millimho and micromho are commonly used by hydroponicists in North America and in earlier scientific literature. The basis for this unit came from the ohm, which is the unit used to measure electrical 'resistance'. A 1 ohm resistance with 1 Volt across it will conduct 1 Ampere of electrical current. The electrical equation is V (volts) = I (ampere) * (times) R (resistance) where R is measured in ohms. The reciprocal of resistance is 'conductance', with the mho (ohm spelt backwards) used to describe conductance.[/FONT]
[FONT="]The scientific literature adopted Millimho per centimetre (mmho/cm) and micromho per centimetre (mmho/cm), where 1mmho/cm = 1000 mmho/cm.[/FONT]
[FONT="]The metric equivalent for mho is Siemens, where 1mho/cm = 1mS/cm = 1000uS/cm. The metric system is used extensively throughout Europe, South Africa, Australia and New Zealand.[/FONT]
[FONT="]For hydroponics, scientific literature generally uses deciSiemens per metre (dS/m) to measure conductivity, with milliSiemens/cm (mS/cm) and microSiemens/cm (S/cm) the established and accepted units of measurement for soilless culture, where 1dS/m = 1mS/cm = 1000uS/cm as measured by a Conductivity meter.[/FONT]
[FONT="]An old unit of measurement is cF (Conductivity Factor). These meters use a scale of 0 to 100, where 0 represents pure water (zero ionic salts). cF is not a recognised scientific measurement, and it has as its basis 1mS/cm = 10cF. cF measurements were first introduced in the United Kingdom during the early development of NFT (Nutrient Flow Technique).[/FONT]
[FONT="]Calibration Solutions[/FONT]
[FONT="]For hydroponics applications there are two requirements. The calibration solution should represents a value close to the expected conductivity of a nutrient solution. The solution should use the same or similar types of ionic salts known to be in the nutrient solution.[/FONT]
[FONT="]The calibration solution most suitable for hydroponics applications is the KCl (potassium chloride) Standard. Standard values used in hydroponics applications are 2760 uS/cm or 1413 uS/cm at 25 OC. TDS standards are also available from TPS. [/FONT]
[FONT="]When to Calibrate[/FONT]
[FONT="]Meters should be calibrated when first used, and then regularly thereafter. Whilst conductivity sensors are generally very stable long term, a regular calibration check will ensure your system is operating correctly. [/FONT]
[FONT="]Checking the calibration should be a routine that uses a fresh calibration solution. The recommended shelf-life for a factory sealed calibration solution is 1 year. Do not mix used calibration solution with new solution. Once the meter has been tested and/or calibrated, the solution should be discarded; not returned to the reagent bottle.[/FONT]
[FONT="]Remember - the accuracy of your measurements can determine the success or failure of your crop. Regular calibration checks in accurate standards may avert disaster ![/FONT]
[FONT="]The Importance of Temperature Compensation[/FONT]
[FONT="]Conductivity requires mobile ions in solution, when the mobility rises because of increases in temperature the conductivity measured also rises. For every 1OC temperature change, the conductivity of a nutrient solution will increase by around 2% (Resh, H.M., 1991). This temperature coefficient varies with the type of salts in the solution, the concentration of those salts and the temperature itself.[/FONT]
[FONT="]When calibrating meters, the calibration solution temperature should be as close as possible to the nutrient solution to be tested, to minimise temperature effected errors.[/FONT]
[FONT="]TPS conductivity meters have an Automatic Temperature Compensation (ATC) feature, which scale the readings to a standard temperature of 25OC. When the temperature deviates from 25OC, then the meter automatically compensates for temperature changes experienced in the nutrient solution.[/FONT]
[FONT="]Meter Ranges[/FONT]
[FONT="]TDS meters suitable for soilless culture should have a range from 0 to 10,000ppM, and Conductivity meters from 0 to 20mS/cm (20,000uS/cm).[/FONT]
[FONT="]TPS manufactures the multi-range, hand-held Aqua-C and WP-84 for agricultural applications. Models that also incorporate a pH readout are the Aqua-CP (single Conductivity range) and WP-81. They also manufacture the purpose-designed hydroCHEM-DS Conductivity and pH dosing controller for hydroponic applications. This unit continuously monitors Conductivity and pH and maintains user-set levels using inbuilt peristaltic dosing pumps.[/FONT]
