What is Conductivity?
Measurement of a solution's ability to conduct an electric current (conductance) per unit of volume.
How does temperature effect conductivity readings?
Depends on the chemical solution. Generally aqueous solutions will read a corresponding +/-2% per change in degree Celsius from baseline.
Can conductivity only be measured in aqueous solutions?
No, all substances have conductivity. Low for organic compounds, high for metallic compounds.
What is a conductivity Cell constant, why are there different ones?
The cell constant is a measure equal to the area normal to the current flow in cm^2 divided by the cm distance between electrodes. The closer the electrode the higher the K and vice versa. Helps bring very conductive or very conductive solutions into range.
How are conductivity and TDS (total dissolved solids) related?
Dissolved substances that contribute to conductivity can have their concentration indicated by their conductivity in solution. Works well for the same source in similar solutions.
How do I calibrate my TDS meter is my dissolved solids are not the same as the ones in the catalog?
Making your own standard from the target dissolved solid will yield more accurate results. Make a solution of your dissolved solid close to the target solution as possible, or within the top third of possible variance. The formula is as follows Xpm TDS= Xmg of salt + 1 liter of distilled water.
The conductivity standard I purchased has three values listed. Which should I use?
It depends on what you are measuring. For conductivity use micromhos or microsiemens. If it is a NaCl solution TDS use ppm/NaCl, if it is the natural water use the 442 formulation (40%sodium sulfate, 40%sodium bicarbonate, 20% sodium chloride).
What is the difference between microohmos and microsiemens?
None, there is a 1 to 1 ratio. Microohmos is the name of the unit in the US while microsiemens is used in Europe.
How do I clean my conductivity cell?
Clean with mild liquid detergent, dilute nitric acid, dilute HCl, and/or dilute H2SO4. by dipping or filling the cell with solution and agitating for 2-3 minutes. Stronger cleaning can be accomplished using concentrated HCl in a 50% water/isopropanol mixture. Rinse with DI water and recalibrate before use.
How often do platinum conductivity cells need to be replatinized?
Cells are coated in platinum black in order to avoid polarization, the build up of ions around the meter to form a screen and prevent accurate readings. To prevent this the platinum should be replaced when it appears ti be flaking/ damaged or every six months.
How should I store my conductivity cell?
Rinse it in tap water after using it. It can be stored wet or dry, but if it is stored dry it will need to be reconditioned before use.
How should I condition my conductivity cell?
with power running to the cell place it in a standard solution or tap water and soak for 30 minutes to an hour unless otherwise specified..
What is the difference between conductivity and salinity?
Salinity is calculated from a conductivity reading using a correction factor specific to the salt being detected. This yields a ppm of the salt, which varies from manufacturer to manufacturer.
How far can the meter be from the cell?
Generally around 200 feet apart.
Is there an expiration date on conductivity standard solutions?
Unopened the solution will last one year. Opened, but contained, the solution will last for 6 months, opened but exposed to air the solution will last one day. Any solution under 100 microsiemens will rise in conductivity more quickly as it evaporates in order to reach equilibrium with the conductivity of the air around it (120 microsiemens). This will quickly ruin the standard.
Are conductivity cells interchangeable with other meters?
No, you cannot place one manufacturer's cell on another manufacturer's meter. The cell constants, thermomistor and pin configuration usually vary.
How and when do I need to calibrate the conductivity cell?
Calibrate the cell using standard solutions in the range of the samples you are testing. Condition it in ones sample of standard, rinse it in a second and run calibration in a third. Adjust the cell constant until the specified value is displayed. recalibrate when changing ranges.
How do I fine the correct temperature coefficient for conductivity when not working in water?
Measure the conductivity at 25 degrees Celsius then repeat at a different known temperature to see the percent change in conductivity. Divide by the difference in degree to obtain the correction factor.
How should I store my DO probes?
Store a DO probe with the membrane covered by distilled water to prevent the KCl fill solution from evaporating through the membrane.
What is the difference between a galvanic and polarographic DO probe?
A galvanic probe usually consists of silver and lead with a potassium hydroxide electrolyte and produces its own current. Polarographic probes usually have a silver anode surrounded by a gold cathode with current supplied by the meter.
How does temperature affect me DO readings?
Temperature affects DO readings in two ways. First it changes the permeability of the membrane to oxygen, becoming more permeable as temperature rises. Second it affects the amount of oxygen able to be dissolved into solution, for instance as temperature increases the saturation point of water decreases. Most meters have automatic compensation for the changes in membrane permeability. For changes in saturation use the correct reference chart for the type of water you are measuring.
I just received my DO meter and it is broken out of the box.
The probe must be allowed to polarize before it can take readings, and must be connected to a meter to polarize. How long the probe needs to polarize is determined by the manual. Also check the membrane, if air is trapped behind the membrane you will have erroneous readings.