Process pH and Conductivity Sensors: How to Choose by Media, Range and Output in Canada

A process pH, conductivity or turbidity sensor stays in the line and sends a continuous signal to a controller, which is the whole difference from a handheld meter. Choose it by the fluid it will sit in (acid, seawater, ultra-pure water, solids), the conductivity range you need to read, and the output your controller or PLC expects. ERE stocks Icon Process Controls sensors for each of these and can match one to your line.

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What Is the Difference Between a Process Sensor and a Handheld Meter?

A handheld meter takes a spot reading when someone is standing at the sample point; a process sensor measures all the time and feeds a controller that can alarm, dose or log. If you need a reading once a shift, use a meter. If a pH excursion or a conductivity spike has to trigger a relay, you need an inline sensor.

Our buyer's guides cover the portable side: the pH meter guide, the portable conductivity meter guide and the ORP meter guide. This guide is for the fixed installation: a sensor on a pipe, tank or sump. The full range sits in the Water Quality Instrumentation collection.

How Do You Choose a pH Sensor for Industrial Process Water?

Choose the pH sensor by the chemistry of the fluid, because the reference junction is what fails first in harsh media. EPA's pH reference for aquatic systems notes that pH is logarithmic, so one unit is a tenfold change in hydrogen ion concentration, and that U.S. EPA freshwater criteria suggest a 6.5 to 9 range. A sensor that drifts by half a unit is a real error at those limits.

Every Icon P14 model uses a PTFE Teflon Nexus double junction designed to resist reference poisoning, a polypropylene body with a 3/4 in NPT connection, temperature compensation and no preamp. Each comes with a flat or bulb electrode (the P14P is bulb only). The difference between models is the media:

Model	Built for
Icon P14C	Harsh, contaminated process media
Icon P14H	Hydrofluoric acid up to 4000 ppm HF
Icon P14F	Hydrofluoric acid above 4000 ppm HF (antimony electrode)
Icon P14S	Seawater and saltwater
Icon P14D	Desulfurization and demanding industrial processes
Icon P14P	Low-conductivity, ultra-pure water

If you also need redox control, the Icon R7G is a general-purpose ORP sensor in the same compact body and with the same output options.

Which Conductivity Sensor Fits Your Range?

Pick the conductivity sensor from the range you must read, because one cell cannot cover ultra-pure water and brine. EPA's conductivity indicator page explains that a significant change, usually an increase, can signal that a discharge or other disturbance has entered the water, which is the reason many sites monitor it continuously.

Model	Range and electrode	Typical use
C250	Ranges down to 2 uS, titanium electrode	Ultra-high-purity water
C350	Up to 2000 uS/cm, 316L stainless tri-clamp (1, 1-1/2 or 2 in)	Sanitary lines
C450	Up to 200,000 uS/cm, titanium or graphite, several cell classes	General process fluids
C850	Up to 500,000 uS/cm, graphite, PP housing	High-conductivity fluids
C950	Up to 200,000 uS/cm, stainless steel, four cell classes	High temperature
C750	Toroidal (inductive), up to 2000 mS/cm, PFA Teflon or PP body, PT1000	Corrosive, coating or fouling media

The C-series double-electrode sensors are temperature compensated and factory calibrated, with direct 4-20mA and RS485 outputs and no conductivity module required. Toroidal sensors have no electrodes in contact with the fluid, which is why they are the usual choice when electrodes would coat or corrode.

When Do You Need a Turbidity, Dissolved Oxygen or Ion Sensor?

Add these when the control question is about solids, aeration or a specific ion rather than pH or conductivity. The Icon TB Series turbidity sensor uses ISO 7027 IR double-scattering light measurement with a quartz glass lens and a 316L stainless steel and POM body, with RS-485 Modbus and 4-20mA outputs and an IP68 housing; the TB550 adds a self-cleaning scraper. For general turbidity method choices see our turbidimeter selection guide.

The Icon DO3000 measures 0 to 20 mg/L by fluorescence quenching with no reagents and an RS485 Modbus RTU output. The Icon IS-750 uses ion selective electrodes for fluoride, chloride, ammonium, nitrate, potassium or calcium.

Which Output and Controller Do You Need?

Confirm the output first, because it decides whether the sensor connects to your existing PLC or needs a controller. The Icon pH, ORP and conductivity sensors are offered with 4-wire output for ProCon controllers, 2-wire 4-20mA, 4-20mA with RS485, or an IO-Link adapter. For display, relays and trending, ERE offers the Icon D720 two-channel pH/ORP controller and the Icon U900 four-channel universal analytical controller. If the signal goes to a transmitter loop, our 4-20mA transmitter guide explains the loop basics, and our flow meter guide covers the flow side of the same panel.

The product records do not publish sensor service life, response time or calibration intervals, so ask for those on the quote for your fluid and temperature.

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Frequently Asked Questions

What is the difference between a pH sensor and a pH probe?

The words are used interchangeably. In process work, "sensor" usually means a fixed electrode assembly, often with built-in temperature compensation and a transmitter output, that is installed in a line or tank.

Can one sensor measure both pH and conductivity?

No. pH and conductivity use different sensing elements, so they are separate sensors, although one controller such as the U900 can accept several sensors.

Which conductivity sensor is best for ultra-pure water?

The Icon C250 high-purity sensor has a titanium electrode and ranges down to 2 uS, so it is the model built for ultra-high-purity water.

What output does an Icon process sensor have?

The pH, ORP and conductivity sensors are offered with 4-wire output for ProCon controllers, 2-wire 4-20mA, 4-20mA with RS485, or an IO-Link adapter.

Do I need a toroidal conductivity sensor?

Consider one when the fluid is corrosive, coats surfaces or reaches extreme conductivity, since a toroidal sensor like the Icon C750 reads up to 2000 mS/cm without electrodes touching the fluid.

Related articles

• pH Meter Buyer's Guide for Canada
• Portable Conductivity Meter Buyer's Guide
• ORP Meter Buyer's Guide for Canada
• Turbidimeter Selection Guide

Lire en français : Capteurs de pH et de conductivité de procédé : guide de choix pour le Canada