pH Electrode with BNC SZ171 | B&C Electronics

The SZ171 is especially suitable for applications where a double junction glass pH combination electrode. B&C Electronics particularly recommends it for contaminating liquids and amplified probes.

Contaminated liquids

• pH measurement in liquids with the presence of contaminants.
• Process water and wastewater.
• Processes where a simple union may suffer premature contamination.
• Water treatment and conditioning systems.
• Applications where the aim is to improve the protection of the internal reference system.

pH instrumentation and measurement

• Measuring systems that accept combined glass/reference electrodes.
• Instruments with high impedance input for pH electrodes.
• Amplified probes.
• Measuring, laboratory or control equipment with compatible electrical connection.

Industrial automation

• pH measurement with PLC relay.
• Conversion of pH measurement to 4-20 mA signal.
• Integration into SCADA systems.
• Transmission via RS485 Modbus using a compatible transmitter.

The reference frame is one of the fundamental parts of a pH electrode. To perform the measurement, there must be ionic contact between the internal reference and the liquid through the electrode connection.

In contaminated liquids, certain compounds can migrate across this junction and gradually reach the reference system. This phenomenon can cause signal instability, zero point shift, or reduced electrode lifespan.

The SZ171 uses a double annular union. This construction introduces an additional separation between the process liquid and the internal reference system, reducing direct contact of contaminants with the reference.

For this reason, B&C Electronics is specifically targeting this model towards applications with polluting liquids.

The SZ171 uses a glass membrane sensitive to hydrogen ion activity. Upon contact with the liquid, an electrical potential difference is generated between the glass electrode and the reference system.

The voltage generated varies depending on pH and temperature. It is a signal of very high impedance and low electrical level, therefore It cannot be directly connected to a conventional voltage or current input of a PLC.

The pH instrument connected to the SZ171 provides the necessary input electronics, performs electrode calibration, and converts the electrochemical signal into a pH reading.

When the measurement needs to be integrated into an automation system, that reading can later be converted into an industrial signal such as 4-20 mA or RS485 Modbus using the corresponding transmitter.

The SZ171 always needs a specific instrument for pH measurement. The type of instrument depends on whether a portable measurement, a local indication, or signal integration into an industrial system is required.

Portable pH meter

For portable measurements, a Portable pH meter compatible with combined glass/reference electrodes.

B&C Electronics has, for example, the PH135, a portable pH, redox and temperature meter with a range of -1.00 to 15.00 pH, resolution of 0.01 pH, manual or automatic calibration, temperature compensation and memory for up to 100 measurements.

Note: In the documentation for the PH135, B&C Electronics specifically recommends the SZ142, SZ161, and SZ1031 electrodes. The SZ171 does not appear explicitly in that list of recommended electrodes, so it is advisable to confirm the specific compatibility of SZ171 + PH135 before specifying this combination.

4-20 mA Transmission: PH3630

To integrate pH measurement into a PLC, recorder, or control system using an analog signal, the following can be used: B&C PH3630.

The PH3630 is a pH transmitter for DIN rail mounting that accepts pH electrodes and provides a isolated 4-20 mA output in two-wire current loop. It is powered by between 10 and 30 Vdc and also allows the connection of a Pt100 for automatic temperature compensation.

The measurement architecture is:

SZ171 electrode → PH3630 transmitter → 4-20 mA → PLC / recorder / control system

4-20 mA and RS485 Modbus: PH3436

When digital communication is needed in addition to the analog output, the following can be used: B&C PH3436.

The PH3436 is a microprocessor-based pH/Redox transmitter that incorporates Isolated 4-20 mA output and RS485 communication. It can work with B&C ASCII protocol or Modbus RTU, allowing the measurement to be integrated directly into PLCs, SCADA systems, or monitoring applications.

Analog output and digital communication can be used simultaneously.

SZ171 electrode → PH3436 transmitter → 4-20 mA + RS485 Modbus → PLC / SCADA

The SZ171 incorporates a BNC connector, while connection to certain industrial transmitters can be made via terminal blocks. In these cases, the following must be used: appropriate electrical termination or adaptation and check the intended wiring for the instrument used.

He B&C PH135 It is a microprocessor-controlled portable pH meter designed to perform measurements of pH, Redox potential and temperature.

• pH range: -1.00 … 15.00 pH.
• Resolution: 0.01 pH.
• Redox Range: -1200 … +1200 mV.
• Redox Resolution: 1 mV.
• Temperature: -10.0 … 110.0 °C.
• Temperature sensor: 3-wire Pt1000.
• Temperature compensation: manual or automatic.
• Calibration: manual or automatic.
• Memory: up to 100 measurements.
• Feeding: 9V battery.

This type of instrument allows us to understand the difference between electrode e measuring instrumentThe electrode generates the electrochemical signal and the PH135 performs the reading, calibration, compensation and display of the pH value.

The PH135 technical data sheet specifically recommends B&C electrodes SZ142, SZ161 and SZ1031. Although the SZ171 also belongs to the family of combined glass/reference electrodes, It is not expressly included by B&C in the list of recommended sensors for the PH135, Therefore, the combination should be verified before offering it as a set.

The models SZ171 and SZ173 B&C Electronics products belong to the same family of combined pH electrodes with glass body and double ring joint. The main difference lies in the wiring and the type of installation for which each model is most practical.

• SZ171: 1.5m cable terminated with a BNC connector. Especially useful when a BNC connection or a short cable length is needed.
• SZ173: 9m cable. B&C Electronics directs it to contaminating liquids and industrial instrumentation and specifies in-line installation up to 10 bar.

Both models have double annular union and are designed for contaminating liquids, but the SZ173 is particularly suitable for fixed industrial installations where there is a greater distance between the measuring point and the instrumentation.

A pH electrode needs periodic calibration using buffer solutions. The frequency depends on the process, the required precision, the temperature, the degree of contamination of the liquid, and the usage time.

To perform a correct calibration, buffer solutions appropriate to the operating range must be used. B&C Electronics offers, among others, reference solutions of pH 4.01, pH 7.00 and pH 9.21.

The glass membrane must be kept clean and properly hydrated. Deposits present in the process can cause longer response times, measurement errors, or difficulty calibrating the sensor.

It is also important to avoid keeping the membrane of a pH electrode permanently dry when the manufacturer's storage instructions require it to be kept hydrated.