Water Quality Sensors: pH, Conductivity, Dissolved Oxygen and Turbidity (Panel vs RS485)
Short answer: for online water-quality measurement you choose between two formats. A panel controller (96×48 or 96×96 mm) takes an analog electrode, shows the value on the panel, gives a 4-20 mA output and switches a relay at a high or low limit. A digital RS485 sensor has the electronics in the probe and is read directly by a PLC, gateway or SCADA over Modbus RTU, with no controller in between. Pick by parameter (pH/ORP, conductivity/TDS, dissolved oxygen, turbidity), then by the signal your system reads, then by supply voltage. Find it by part number. Buy it with the specs in front of you.
Specs at a glance: pH and ORP
| Product | Format | Range (as listed) | Outputs | Supply | Price |
|---|---|---|---|---|---|
| PH-110 panel pH / ORP controller | Panel, 96×96 mm (cut-out 92×92); sold with a pH or ORP electrode, 5 m cable | pH 0-14 (±0.02 pH); ORP -1000 to +1000 mV; NTC10K temperature compensation | Isolated 4-20 mA + 2 alarm relays (250 VAC 3 A) | 220 VAC ±10 % | $229.99 – $295.99 |
| Online pH controller / transmitter | Wall/panel unit with LCD; electrode not stated as included | 0.00-14.00 pH, 0.01 pH resolution; three-point calibration | 4-20 mA + RS485 Modbus RTU | 85-265 VAC or 9-36 VDC | $479.99 |
| Digital pH sensor, RS485 Modbus | Digital probe, PG13.5 thread, PTFE junction | 0-14 pH; 0-130 °C; up to 0.6 MPa | RS485 Modbus RTU | Not stated in the listing | $650.99 |
Specs at a glance: conductivity, TDS, dissolved oxygen and turbidity
| Product | Measures | Range (as listed) | Outputs | Supply | Price |
|---|---|---|---|---|---|
| PSC-54 conductivity / TDS controller | EC / TDS, 1 sensor (1/2″ thread, 3 m) | 0-9999 µS/cm or 0-20 mS/cm; 0-9999 ppm TDS; ±1.5 % | 4-20 mA + 1 high/low relay (2 A) | 220 VAC ±10 % (not 120 V) | $151.99 |
| Dual-channel conductivity / TDS controller | EC / TDS, 2 sensors (1/2″, 3 m) | 0-9999 µS/cm or 0-20 mS/cm; ±2 % | 4-20 mA + high/low ON/OFF relay | 110 VAC | $192.99 |
| Submersible conductivity / TDS / salinity sensor | EC, TDS, salinity, temperature | K=1: 1-10,000 µS/cm; K=10: 10-100,000 µS/cm; ±1.5 % FS | RS485 | 7-30 VDC; IP68, 5 m cable | $117.99 |
| Optical dissolved oxygen sensor (analog) | DO, fluorescence; freshwater | 0-20 mg/L (0-200 % sat.); ±3 % FS; ≤60 s response | 4-20 mA, 0-5 V or 0-10 V | 10-30 VDC | $226.99 – $233.99 |
| Renke RS-LDO-N01 optical DO sensor | DO, fluorescence; freshwater or seawater version | 0-20 mg/L; ±3 % FS | RS485 Modbus | 10-30 VDC | $233.99 – $256.99 |
| YM1118B infrared turbidity sensor | Turbidity, infrared optical | 0-1000 NTU; ±3 % FS | RS485, 9600 bps default | 6-24 VDC; IP67, 1 m cable | $102.99 |
Which one fits my application?
| Application | Look at | Why |
|---|---|---|
| Cooling tower or boiler blowdown on conductivity | PSC-54 (220 VAC) or dual-channel controller (110 VAC) | High/low relay to drive a blowdown valve or alarm, plus 4-20 mA to the PLC |
| RO system: feed and permeate conductivity on one panel | Dual-channel conductivity controller | Two sensor inputs in one 96×48 mm cut-out |
| Neutralization or chemical dosing on pH | PH-110 (electrode included) or online pH controller (wide-range or 24 VDC supply) | Alarm relays and 4-20 mA; the online unit also has RS485 Modbus |
| Several parameters on one Modbus bus to a PLC, RTU or SCADA | RS485 sensors: digital pH, submersible conductivity, Renke DO, turbidity | One 2-wire RS485 cable, one address per sensor, no controller per parameter |
| Aeration basin or fish tank DO into an existing analog card | Optical DO sensor with 4-20 mA / 0-10 V | Analog output; fluorescence sensor with no membrane to refill (film life about 1 year per supplier) |
| Seawater, brine or produced water | Conductivity sensor with K=10 electrode; Renke DO seawater version | K=10 reads up to 100,000 µS/cm; seawater DO version listed separately |
What goes with a water-quality sensor
- Put 4-20 mA values on Modbus: the 4AI-4DI-4DO Modbus RTU module ($33.99 – $34.99) reads 4 analog inputs onto RS485.
- Send RS485 readings over Ethernet, WiFi, cellular or LoRa: see our RS485 Modbus gateway guide.
- Choosing between analog signals: 4-20 mA vs 0-10 V. Measuring temperature at the same point: Pt100 and temperature transmitter guide.
Questions buyers ask
Panel controller or RS485 digital sensor?
Choose a panel controller when an operator needs to read the value at the panel and a relay must act at a set point without a PLC. Choose an RS485 digital sensor when a PLC, RTU or SCADA already handles display and logic: you wire several sensors on one bus and read each by Modbus address.
Is the pH electrode included?
It depends on the listing. The PH-110 is sold with a pH or ORP electrode on a 5 m cable (choose the body type). The online pH controller listing does not state that an electrode is included, so plan a compatible pH electrode. The digital pH sensor is itself the probe.
What is the K=1 / K=10 option on a conductivity sensor?
K is the electrode cell constant. K=1 covers 1-10,000 µS/cm (tap, process and RO feed water); K=10 covers 10-100,000 µS/cm (brine, seawater, concentrated solutions). Pick the one whose range includes your normal reading.
Do these controllers run on 120 V?
Check the supply column. The dual-channel conductivity controller is the 110 VAC version. The PSC-54 and PH-110 are 220 VAC. The online pH controller accepts 85-265 VAC or 9-36 VDC. The RS485 conductivity, DO and turbidity sensors and the analog DO sensor run on low-voltage DC; the digital pH sensor listing does not state its supply.
What is the difference between optical and membrane dissolved oxygen sensors?
Both DO sensors listed here are optical (fluorescence). They have no electrolyte or membrane to refill; the supplier states a fluorescent film life of about one year in normal use. Response time is listed as 60 s or less.
Can I use one of these for drinking-water compliance reporting?
No listing includes a third-party certification or regulatory approval. Use them for process monitoring and control; for compliance reporting, use instruments and methods your regulator accepts.
Can a pH or conductivity controller relay be a safety interlock?
No. None of these units carries a safety (SIL) rating. Use the relays for process alarms and dosing or blowdown control, not as the only protection of a safety function.
See every reading on one screen: AutomationBotX Cloud
Once your pH, conductivity, DO or turbidity values reach a Modbus gateway, AutomationBotX Cloud shows live readings, trends and alarms in the app on one dashboard. It is read-only monitoring: it never sends commands to your equipment, so it does not replace a control or safety system. First 10 machines free, no card needed. How the signal gets from the sensor to your phone.
Need several units?
Ask for a written volume quote on our wholesale page. More sensors: IoT sensors.
Free US shipping on every order. Specs above come from the product listings; if a value you need is not listed, it is not stated by the supplier. Prices checked on November 14, 2026 and may change; the product page shows the current price.