Differential Electrode Design

How Does a Differential pH Sensor Work?

Differential pH sensors and ORP sensors employ a field-proven method that uses three electrodes instead of the two used  in conventional pH sensors. The key difference is in the reference cell design. While a combination pH electrode has an Ag/AgCl reference wire in KCl solution, a differential pH sensor reference is actually a measuring pH electrode in a known pH 7.0 buffered cell solution. This reference cell (E2 in the figure on the left) makes electrical contact with the process via a double junction salt bridge. The other measuring pH electrode (E1) is in direct contact with the process. The process and reference electrodes measure the pH differentially with respect to a third metal ground electrode (E3).

Why Does a Differential pH Sensor Last Longer?

The main advantage of using a reference electrode in buffered electrolyte solution rather than in KCl is that the buffered solution resists pH change. Over time, liquid from the process can contaminate or dilute the reference. However, with a buffered electrolyte reference, an accurate reading can be maintained even with some contamination. Differential pH sensors are manufactured so the double junction salt bridge and the reference cell buffer may be removed and replaced in the field. Compared to conventional combination sensors, differential pH sensors provide measurements of greater stability over longer periods of time with less downtime and maintenance.

Benefits of the Differential Measurement Technique

The differential measurement technique addresses some of the challenges of using pH and ORP electrodes in water, wastewater and coating industrial applications. Hover over the flip boxes to learn about the key features of the differential design.

Built for Tough Applications

Sample constituents in industrial and wastewater applications typically contaminate the sensor reference, leading to measurement inaccuracy.

Buffered Reference Solution

Differential sensors contain buffered electrolyte solution, which maintains its pH level with minimal dilution effects.

High Accuracy Measurements

Ground loop measurement error occurs when there is a voltage drop across the reference due to build up of coating on the sensor surface.

Built-in Solution Ground

Differential measurement with respect to the integral solution ground electrode virtually eliminates ground loop measurement errors.

Cost-effective Design

Clogged junctions and reference fouling are common causes of sensor failure. The cost of constantly replacing failed sensors adds up quickly.

Extended Sensor Lifetime

Differential pH sensors are manufactured so that the double junction salt bridge and buffered reference cell solution may be removed and replaced in the field. Why replace entire pH sensors when you can recondition and extend the sensor life?

CHOOSE A DIFFERENTIAL pH SENSOR OR ORP SENSOR FOR YOUR SYSTEM

We are pleased to announce the addition of two new differential pH and ORP sensors to our product lineup. In addition to the SD7000 5-wire Hach/GLI direct replacement sensors, Sensorex will now offer the power of differential pH and ORP measurements, but with direct 4-20mA output (SD7420) or universal combination output (SD7500) models!

SD7000 Series

SD7000 5-Wire Differential Online Process pH Probe

Already have a differential pH sensor? Direct fit replacements for:

  • Hach® 6028P0 and 2028R0
  • Hach® 6022P0 and 2022R0
  • Water Analytics® P60C-8

SD7420 Series

differential pH sensor

Don’t want to purchase a transmitter or controller?

Direct 4-20mA output allows integration into a process control system without the use of a transmitter or controller.

SD7500 Series

differential ORP probe

Don’t want to replace your transmitter or controller?

Combination sensor output for deployment flexibility with various transmitters and controllers.

Specifications for Differential pH and ORP Sensors

All of our differential pH sensors and differential ORP sensors feature a two year limited warranty.

pH MEASUREMENT RANGE: 0-14

pH STABILITY: 0.03pH per 24 hours, non-cumulative

ORP MEASUREMENT RANGE: -2000mV to +2000mV

TEMPERATURE RANGE: 0-95°C (32-203°F)

TEMPERATURE COMPENSATION: 300Ω NTC

TRANSMISSION DISTANCE: 914 m (3000 ft)

pH MEASUREMENT RANGE: 0-14

pH STABILITY: 0.03pH per 24 hours, non-cumulative

ORP MEASUREMENT RANGE: -2000mV to +2000mV

TEMPERATURE RANGE: 0-85°C (32-185°F)

TEMPERATURE COMPENSATION: 10K NTC

TRANSMISSION DISTANCE: 914 m (3000 ft)

pH MEASUREMENT RANGE: 0-14

pH STABILITY: 0.03pH per 24 hours, non-cumulative

ORP MEASUREMENT RANGE: -2000mV to +2000mV

TEMPERATURE RANGE: 0-85°C (32-185°F)

TEMPERATURE COMPENSATION: PT1000 RTD

TRANSMISSION DISTANCE: 914 m (3000 ft)

Accessories for Differential pH and ORP Sensors