Water Conductivity Measurement: Should You Choose a K1 or K10 Probe?

You want to set up water conductivity measurement on a well, a process water loop or the outlet of a treatment plant, and you are looking at two probes that look exactly the same: one labeled K1, the other K10. The short answer: if your water reliably stays below 2,000 µS/cm, the K1 probe is the more accurate choice. If values can climb higher, you need the K10 probe, which in the Dragino lineup covers up to 20,000 µS/cm.

A quick recap first. The EC value describes how well water carries an electric current. It rises with the amount of dissolved salts and is usually reported in µS/cm, referenced to 25 °C. This guide is about which measuring cell captures your range cleanly, how to calibrate it and how to install it so it keeps delivering useful data for months.

How do you measure water conductivity?

Every conductivity measurement works on the same principle. Two electrodes sit in the water, the electronics apply an alternating voltage and measure how much current flows. That gives you conductance in siemens. Alternating voltage is used because direct current would pile up ions at the electrodes and distort the reading. Conductance alone depends on electrode size and spacing, though. Only the cell constant turns conductance into the specific conductivity you read in µS/cm.

Because conductivity depends heavily on temperature, good probes measure the water temperature at the same time and convert the reading to a reference temperature, usually 25 °C. Without that compensation, your value would rise during the day simply because the water warms up, even though nothing about its composition has changed.

In practice there are two routes. A handheld conductivity meter is the right tool for spot checks: dip it in, read it, write it down. If you want to see trends, watch limits or trigger alarms, you need a permanently installed probe with a digital interface. The Dragino DR-ECK1.0 and DR-ECK10.0 belong to that second group. They report conductivity and temperature over RS485 using Modbus RTU at 9,600 baud, run on 7 to 30 V DC at less than 0.5 W and come with a 5 m (16 ft) cable. A controller, a data logger or an RS485 radio node that forwards the values over LoRaWAN, for example, reads them out.

What is the conductivity cell constant?

The cell constant, often called the K factor, describes the geometry of the measuring cell. In the idealized case it is the distance between the electrodes divided by their effective area, expressed in cm⁻¹. Conductivity equals the measured conductance multiplied by the cell constant. In the textbook picture, a K1 cell is two plates of 1 cm² each, 1 cm apart. In a K10 cell that ratio is ten times larger, because the electrodes are smaller or farther apart.

What does that mean for the reading? In the same water, a K10 cell passes only a tenth of the current that a K1 cell would. In highly conductive water that is an advantage: the electronics do not saturate and less polarization builds up on the electrodes. In low-mineral water, however, the current gets so small that fine differences disappear in the noise. That is why there is no single best cell, only the right cell for each range.

Two misconceptions come up again and again. First, a higher cell constant is not a quality grade; it is an adaptation to a different measuring range. Second, the nominal value on the label is not exact. Electrode shape and the electric field around it mean the real cell constant of your probe differs slightly from the nominal figure. Calibration with a standard solution corrects exactly that difference, so there is no need to measure the electrodes or work out a correction factor yourself.

K1 vs K10 conductivity probe: which range do you need?

Three numbers drive the choice: the normal value of your water, the lowest value that still matters to you and the highest value that can realistically occur. Dragino specifies the DR-ECK1.0 for 0 to 2,000 µS/cm at 1 µS/cm resolution and the DR-ECK10.0 for 10 to 20,000 µS/cm at 10 µS/cm resolution. Both models have an accuracy of ±1% of full scale.

That accuracy figure is the real key to the decision. One percent of 2,000 µS/cm is ±20 µS/cm, and one percent of 20,000 µS/cm is ±200 µS/cm, and those tolerances apply across the whole range. If you measure well water at around 650 µS/cm, the K1 probe may be off by about 3%, while the K10 probe may be off by about 30%. In the same water, the larger cell tells you much less, even though its reading shows just as many digits.

The reverse holds too. If your value can climb to 8,000 µS/cm during flushing or a salt intrusion, for example, the K1 probe is outside its range and stops delivering usable data. In that case, the K10 probe is the only option of the two.

The tricky case is a normal value that suits the K1 well, with occasional peaks above 2,000 µS/cm. Ask yourself which information matters more: fine resolution day to day, or the actual height of the peaks. If knowing that the range was exceeded is enough, the K1 probe still makes sense. If you need to quantify the peaks, go with the K10.

Which cell constant suits fresh water, process water or wastewater?

If you do not know your range yet, typical orders of magnitude are a good starting point. The table below maps common water types to the two cell constants. The values are rough guides that vary widely by region and process.

For fresh water, the K1 probe is almost always right. Germany’s Drinking Water Ordinance sets the limit at 2,790 µS/cm at 25 °C, and ordinary tap or well water usually sits far below it. With rainwater or reverse osmosis water, though, the K1 reaches its limit: with a tolerance of ±20 µS/cm, you cannot reliably tell 15 from 30 µS/cm. True ultrapure water applications need specialized cells with a smaller cell constant.

With process water, everything depends on the process. Cooling loops concentrate through evaporation, so conductivity climbs over weeks to several times the makeup water value. That rise is exactly what you want to monitor, so the upper range has to be enough. Wastewater often sits in the transition zone around 2,000 µS/cm and swings with rain events and discharges. Planning with a K1 there means losing the most important events. Seawater, finally, is well beyond both ranges.

Dragino DR-ECK1.0 vs DR-ECK10.0: what is the difference?

From the outside you can barely tell the two probes apart. Housing, cable, connector and protocol are identical. The difference lies in the electrode and in a few communication details. The table summarizes the figures from the Dragino documentation.

Both models share the RS485 interface with Modbus RTU, the 7 to 30 V supply, IP68 protection, a maximum pressure of 0.6 MPa (about 87 psi) and the 5 m cable. Both measure temperature from −20 to +60 °C with 0.1 °C resolution and ±0.5 °C accuracy. Temperature compensation works between 0 and 60 °C and converts to 25 °C by default.

One detail is easy to miss when swapping probes: both deliver a raw register value that your software multiplies by the cell constant. Dragino illustrates this with an example: the same raw value of 686 means 686 µS/cm on the K1 probe and 6,860 µS/cm on the K10 probe. If you change the probe without adjusting the scaling, your reading is off by a factor of ten. The address changes as well: a query sent to 0x12 goes unanswered by a K10 probe with factory settings. So for every measuring point, write down which model is installed with which address and scaling.

How do you calibrate a conductivity probe?

The Dragino probes use one-point calibration. You need distilled water, the matching standard solution and a way to send Modbus commands to the probe, such as a USB-to-RS485 adapter with a Modbus utility on a laptop.

The procedure is short. First, rinse the electrode in distilled water so that residue from the process does not contaminate the solution. Then immerse it in the standard and wait until both conductivity and temperature stop changing. Only then send the calibration command with the solution’s nominal value, multiplied by ten according to the documentation, so 14,130 for 1,413 µS/cm. The probe acknowledges the command, and you read the value once more to confirm it.

A few mistakes cost accuracy more often than others. Air bubbles between the electrodes reduce the effective area and fake a reading that is too low, so move the probe gently after immersing it. If the solution is colder or warmer than the probe, the temperature sensor needs a few minutes to catch up, and calibrating too early stores a temperature error along with the calibration. And according to Dragino, a probe that has been stored dry for a long time should soak in distilled water for several hours before use so the electrode surface is wetted again.

Dragino recommends calibrating before each use and roughly every three months in continuous operation. In heavily contaminated water or where deposits form, check more often. Slow drift while the process is unchanged is a good warning sign.

Which conductivity standard solution should you use?

The solution depends on the cell constant. For the K1 probe, Dragino specifies the 1413 µS/cm standard; for the K10 probe, 12.88 mS/cm, which is 12,880 µS/cm. Neither number is arbitrary: 1,413 µS/cm is the conductivity of a 0.01 mol/L potassium chloride solution at 25 °C, and 12.88 mS/cm is that of a 0.1 mol/L solution. That is why practically every lab supplier carries them, and you can use them to check any conductivity meter as well.

What matters is that the calibration point lies inside the probe’s working range. Calibrating a K10 probe at 1,413 µS/cm would use a point at the bottom of its range, where its ±200 µS/cm tolerance is already a large share of the value. Stick to the pairing from the documentation.

Handling the solution follows a few simple rules. Pour a small amount into a clean container and discard it afterward; never pour it back into the bottle. Rinse the probe with distilled water before immersing it, then briefly with a little standard so that no film of water dilutes it. Open bottles change over time because water evaporates and carbon dioxide from the air dissolves in. Watch the expiration date and record the lot number together with the calibration date. The nominal values apply at 25 °C. Many labels also list values for other temperatures.

How do you install a conductivity probe to avoid bubbles and deposits?

A well-calibrated probe still reads wrong if it sits in the wrong place. Dragino lists several acceptable mounting styles: through the side wall of a tank, from above on a flange, in a pipe bend, in a flow-through fitting or freely submerged. What they all have in common is that water flows fully around the electrodes and is renewed constantly.

The documentation explicitly describes two installation mistakes. If the fitting is too long and the probe does not reach far enough into the pipe, you get a dead zone where old water stands still. The second mistake is mounting at a high point or in a pipe that is only partly full. Air collects there, and every bubble between the electrodes makes the reading jump or drop. A pipe bend or a section with rising flow, where the pipe always stays full, is the safer choice.

Deposits are the second long-term problem. Scale and other mineral films act like an insulating layer and make conductivity slowly read too low. For calcium and magnesium deposits, Dragino recommends a 10% citric acid solution; for organic fouling, warm water with dish soap or alcohol. Never wipe the electrode surfaces, because that damages the platinized coating. Cleaning here means soaking and swirling in liquid.

Also plan the installation so you can remove the probe without much effort. A ball valve ahead of a flow-through fitting or a bracket in the tank saves time at every calibration. Stay within the datasheet limits: a maximum of 0.6 MPa and an ambient temperature between 0 and 60 °C. The connector at the cable end should stay dry and protected from condensation.

Where can you buy a conductivity sensor?

Before you decide, run a quick check against your measuring point. First, pin down the highest value that can realistically occur and the normal value you see day to day. If both stay safely below 2,000 µS/cm, the K1 cell gives you better accuracy. If your values go beyond that, the K10 cell is the right one.

Next, confirm that your controller or radio node can read RS485 with Modbus RTU and that your supply falls within 7 to 30 V. Settle on the matching calibration solution at the same time, 1,413 µS/cm for K1 or 12.88 mS/cm for K10, and schedule the recalibration. Finally, sort out the mounting location: fully flowed through, free of dead zones and air, and accessible enough for regular cleaning.

If you are planning water conductivity measurement and need a suitable probe, you can find both Dragino models in our Conductivity category.