Say you want to know whether the pH in a pond, a well, a process tank or a wastewater sump stays stable for weeks, and a weekend test strip no longer cuts it. Here is the short answer to how a pH probe works: a glass electrode in the probe produces a small voltage that changes with the acidity of the water. Electronics convert that voltage into a pH value, taking temperature into account, and a transmitter sends the value at fixed intervals to a system that records the trend.
For a trustworthy record, three parts have to work together: the probe sitting in the water, the electronics that turn its signal into a number, and the link that carries the number to your dashboard. Most real-world problems start at the probe, not the radio. The Dragino DR-PH01 probe and the WQS-LB LoRaWAN transmitter let you walk through each step with real datasheet numbers.
How does a pH sensor work?
pH describes how acidic or alkaline water is. Formally, it is the negative base-10 log of hydrogen-ion activity. The practical scale runs from 0 to 14, with neutral at pH 7 at 25 °C. Because the scale is logarithmic, a drop from pH 7 to pH 6 means ten times the hydrogen-ion activity, and a drop to pH 5 means a hundred times.
At the heart of almost every pH sensor for water is a glass electrode. Its tip is a thin bulb of special glass filled with a buffer solution of known pH. When the glass membrane touches the sample, a hydrated layer forms on its surface, and a voltage develops across the membrane that depends on the difference in hydrogen-ion activity inside and outside. To measure that voltage you need a stable point of comparison: the reference electrode, usually a silver wire coated with silver chloride in a potassium chloride solution. A small porous plug called the reference junction connects the reference system to the sample and closes the circuit. In modern probes, the measuring and reference electrodes almost always share one body, known as a combination electrode.
Ideally, this electrode produces about 0 mV at pH 7 and roughly 59 mV per pH unit at 25 °C, positive on the acidic side and negative on the alkaline side. The signal has an extremely high impedance and must be amplified close to the electrode.
One important limit: pH only describes acidity. It tells you nothing about bacteria, nitrate, lead, pesticides or anything else dissolved in the water. A normal-looking pH reading is therefore not a verdict on whether water is safe to drink. Only a laboratory analysis against the applicable drinking-water regulations can answer that.
pH probe vs pH electrode vs transmitter: what is the difference?
The pH electrode is the electrochemical element itself: glass membrane, reference system and reference junction. A pH probe is that electrode in a rugged housing with a cable, often with a temperature sensor and, depending on the design, its own electronics. The transmitter powers the probe, reads its value and passes it on, traditionally as a 4–20 mA signal to a controller, and increasingly as a digital or wireless message.
The Dragino DR-PH01 is a digital probe. It measures pH from 0 to 14 and water temperature from 0 to 60 °C, converts both internally and outputs them over RS485 using Modbus RTU at 9600 baud. It needs a 7 to 30 V DC supply and draws less than 0.5 W. As a standard Modbus device, it also works with a PLC or data logger with an RS485 port, which is how many industrial pH sensors are integrated.
The WQS-LB is the matching transmitter for wireless use. It combines a battery, a switchable 12 V output for the probes, an RS485 interface and a LoRaWAN radio, and it can read one to three water quality probes at once: besides pH, for example, conductivity, ORP, dissolved oxygen or turbidity. According to Dragino, the WQS-LB does not include a probe, so a complete monitoring point needs both parts.
The pH meter vs pH probe question comes up often. A handheld pH meter combines an electrode and a display for spot checks: ideal for checking an installed probe now and then, but no replacement for continuous monitoring.
How do you measure pH continuously in water?
For continuous monitoring, the probe stays in the water permanently while the transmitter wakes up at fixed intervals. The WQS-LB switches on power to the probe, waits a configurable time for the reading to settle, reads it over Modbus, transmits it and switches the probe off again. Out of the box it sends every 20 minutes, which works out to 72 readings a day. You can change the interval with an AT command or a downlink.
For slowly changing water such as a pond or a large storage tank, that is plenty for a meaningful trend. Catching short events, like a flush of wastewater, takes a shorter interval and more battery. Sending more often does not make the electrode faster, though: depending on its condition, a glass electrode takes seconds to minutes to settle on a new value.
Two things set continuous monitoring apart from spot checks. First, the glass membrane must stay wet at all times; once it dries out, it responds slowly or not at all. Second, a freshly installed probe needs time to adapt to the water. Dragino notes that the first readings in new water are inaccurate and that the measurement becomes more reliable after about two hours in the water. Don’t use readings from the first few hours after installation or cleaning to trigger alarms.
Why does pH measurement need temperature compensation?
Temperature affects pH in two ways, and only one of them can be corrected. The first concerns the electrode: the voltage per pH unit rises with temperature, from about 54 mV at 0 °C to 59 mV at 25 °C and roughly 66 mV at 60 °C. According to Hanna Instruments, the resulting error is about 0.03 pH per 10 °C of temperature difference for every pH unit away from pH 7. Measure water at pH 10 and 15 °C without compensation, and you are off by around 0.09 pH. Near pH 7, the effect is small.
Temperature compensation corrects exactly that electrode effect. What it cannot do is cancel the second effect: the water itself changes its pH with temperature because chemical equilibria shift. Even pure water has its neutral point at about pH 6.6 at 50 °C rather than at pH 7.
In practice, always store the temperature together with the pH value. The DR-PH01 measures it itself to within ±0.5 °C, and the WQS-LB includes it in every message. Dragino’s documentation is not consistent on whether the DR-PH01 compensates automatically with its measured temperature or with a set temperature (25 °C by default), so check the documentation for your firmware before relying on tenth-of-a-pH accuracy in very cold or warm water.
How accurate is a pH probe?
The DR-PH01 datasheet lists a resolution of 0.01 pH, a repeatability of ±0.02 pH and an accuracy of ±0.15 pH. Resolution is the smallest displayed step, repeatability is how closely repeated readings of the same water agree, and accuracy is how far the displayed value may be from the true value.
For continuous monitoring, the distinction matters: a repeatability of ±0.02 pH means you can see changes in the trend much more finely than the absolute accuracy suggests. An accuracy of ±0.15 pH, on the other hand, means a displayed 7.20 could really be 7.05 or 7.35. Because the scale is logarithmic, that equals an uncertainty of roughly 40 percent in hydrogen-ion activity. For monitoring ponds, process water or wastewater, that is usually enough; for lab results with two reliable decimal places, it is not.
How close a pH probe stays to its datasheet accuracy depends mainly on the condition of the electrode. Coatings, a clogged reference junction or an aged glass membrane shift the zero point and slow the response. Low-ionic water such as rainwater or deionized water makes readings settle more slowly and wander more. Calibration with buffer solutions is a topic of its own; for long-term use, Dragino recommends it roughly every three months. A value that drifts slowly for no visible reason usually points to the electrode rather than a real change in the water.
How long does a pH probe last?
A pH probe is a consumable, and its glass membrane ages even on the shelf. Dragino rates the DR-PH01 for a lifespan of one year under normal use, and the manufacturer’s warranty on the probes is six months. How long yours actually lasts depends heavily on the water.
Typical signs of aging are longer settling times, readings that no longer recover after cleaning, and a shrinking voltage per pH unit. Wear speeds up with heat, strongly acidic or alkaline water, oil, scale and biofilm on the glass, and a fouled reference junction. The fastest way to ruin a probe is letting it dry out.
That is why the DR-PH01 ships with a storage cap holding a little storage solution that keeps the glass bulb and junction wet. Before use, Dragino says the cap and the blue foam pad must be removed completely. When you take the probe out of the water later, rinse it and put it back in the cap with storage solution, meaning potassium chloride solution, not distilled water, which leaches the electrode.
If a probe becomes sluggish, Dragino describes a reconditioning step: 24 hours in dilute hydrochloric acid (0.1 mol/L), followed by 24 hours in potassium chloride solution. That can revive a tired membrane, but not an aged one, so budget for replacement from day one.
Where should you install a pH probe?
Where you install the probe decides what your reading represents. The DR-PH01 has a 3/4-inch thread at the top and supports two mounting methods. For submerged installation, you run the cable through a waterproof pipe and screw the probe onto the end with thread seal tape. Dragino requires that the top of the probe and the cable exit stay out of the water, even though the probe is rated IP68. For pipeline installation, you screw it straight into the line via the 3/4-inch thread. The maximum pressure is 0.6 MPa (about 87 psi), and the permitted water temperature is 0 to 60 °C.
Within a tank, place the probe where the water is well mixed and represents the water you actually want to know about. Right next to a dosing point or an inlet, you will measure short spikes; in a dead corner, you will measure stagnant water. Keep it away from the surface, with its air bubbles, and from bottom sludge. Many manufacturers recommend mounting glass electrodes tip down at an angle of at least 15 degrees from horizontal, so the air bubble inside does not sit at the glass bulb.
Plan for maintenance, too: if you cannot return the probe to exactly the same spot after cleaning, readings before and after service won’t be comparable. Outdoors, winter matters: below 0 °C the probe is outside its operating range, so for ponds that can freeze, store it in its cap over the winter. The WQS-LB itself stays dry above the water, and the 5 m probe cable gives you room to mount it where the antenna has a clear view.
LoRaWAN pH sensor: how do readings reach your dashboard?
With a wireless setup, every reading follows a fixed path. The probe hands it over RS485 to the WQS-LB, which sends it as a LoRaWAN message to a gateway in range. The gateway forwards it to a network server such as The Things Stack or ChirpStack, where a decoder turns the bytes into values for your database or dashboard. The WQS-LB supports LoRaWAN 1.0.3, including the EU868 and US915 bands.
The message is compact. Alongside the battery voltage, it carries a section for each connected probe, with pH value and temperature for the pH probe. Dragino’s manual gives the example of hex 02DE, which is 734 and, divided by 100, pH 7.34.
A useful detail is the built-in data log. The WQS-LB waits for a confirmation from the network for every message. If none arrives, it stores the reading with a timestamp and sends the backlog once the connection is restored. Your system should distinguish measurement time from arrival time, so a late reading does not look like a new event.
For alarms, derive thresholds from your own application and trigger only when the value stays out of range across several readings. Missing messages deserve their own alarm, because a missing reading is not the same as a bad pH value. The WQS-LB runs on a non-rechargeable 8500 mAh lithium thionyl chloride battery. Its life depends mainly on the reporting interval and how long the probes are powered per reading.
Where can you buy a pH probe for continuous water monitoring?
Before you pick a model, write down the conditions at your measuring point. What water are you measuring, what pH range does it cover, and how warm or cold does it get over the year? If the temperature falls outside 0 to 60 °C or the pressure exceeds 0.6 MPa, a standard probe like the DR-PH01 is not the right choice. Then decide on mounting: submerged on a pipe or threaded into a line, both with a 3/4-inch thread.
Also check how the reading gets out. A digital RS485 probe needs a transmitter or controller with the right interface and power supply; for sites without power or a network, a battery-powered LoRaWAN transmitter such as the WQS-LB plus a gateway in range is the obvious route. Budget for the probe as a consumable with about a year of life, keep storage solution and an easily accessible mounting point for maintenance, and always log temperature and measurement time.
If you are looking for a suitable pH probe or pH sensor, you will find our models in the pH sensors category.