Milwaukee CD611 EC meter

A simple pocket conductivity meter with a wide range to 20,000 µS/cm and automatic temperature compensation.

The Milwaukee CD611 is designed for water analysis: from nearly pure water to distinctly salty solutions. Accuracy ± 2% of full scale, supplied complete in a storage box with protective cap, calibration screwdriver, batteries and instructions. Around 350 hours per set of batteries.

µS/cm or mS/cm: same measurement, different unit

This meter reads in µS/cm while most growing meters work in mS/cm or EC. That is not a different kind of measurement. It is the same quantity in another unit, and the conversion is worth learning once.

The rule is simple: 1 mS/cm is 1000 µS/cm. And what growers call "EC 1.8" is just 1.8 mS/cm.

• EC 0.4 = 0.4 mS/cm = 400 µS/cm
• roughly where much tap water starts
• EC 1.2 = 1.2 mS/cm = 1200 µS/cm
• a light nutrient solution
• EC 2.0 = 2.0 mS/cm = 2000 µS/cm
• a strong solution in flower
• EC 2.77 = 2770 µS/cm: the value of the familiar calibration solution

Do note this meter's resolution of 100 µS/cm. It reads in steps of 100, which is steps of 0.1 EC. For watching your source water or your stock, that is fine. To see differences of 0.05 EC you need a finer step: a meter with 0.01 mS/cm resolution, for instance.

The wide range to 20,000 µS/cm is the other side of the same coin: you can measure water well outside an ordinary growing meter's range, such as brackish water or a concentrated stock solution.

Technical Specifications:

• Range: 0 to 20,000 µS/cm
• Resolution: 100 µS/cm
• Accuracy: ± 2% of full scale
• Temperature compensation: automatic, 5 to 50 °C
• Environment: 0 to 50 °C, max. 95% relative humidity
• Battery: 4 x 1.5 V alkaline (included), approx. 350 hours continuous use
• Dimensions: 150 x 30 x 24 mm
• weight: 85 g
• Supplied with: storage box, protective cap, screwdriver, batteries, instructions

Frequently asked questions

Can I measure my nutrient solution with it?
Yes, that sits comfortably inside the range. Bear in mind you read in steps of 0.1 EC, so fine adjustments will not show.

What is the difference from a meter reading in EC?
Only the unit. Divide the µS value by 1000 and you have the EC.

Does it show TDS or ppm?
This one reads in µS/cm. Ppm is a conversion using a factor that varies by brand; working in conductivity avoids that confusion.

Does it need calibrating?
Yes, at one point, with the screwdriver supplied. A conductivity sensor drifts little, so often is not necessary: keeping it clean matters more.