Digital pH Meter for Water/Food

The pH meter and pH/ORP electrode selection

Wiring diagram:

Definition of the ports

• INPUT: Measuring terminal of the electrode
• REF: Reference terminal of the electrode
• NC: Undefined
• A: Temperature compensation terminal A, connect to NTC 10K or PT1000
• B: Temperature compensation terminal B, connect to NTC 10K or PT1000
• C: Temperature compensation terminal C, connect to 3-wire PT1000 GND (3-wire PT1000), or connect to B (2-wire PT1000), or NC (NTC 10K)
• RS485 (A+): RS485 communication interface A+
• RS485 (B-): RS485 communication interface B-
• 4-20mA (+): 4-20mA output terminal +
• 4-20mA (-): 4-20mA output terminal -
• AC 220V/110V (L) or DC 24V (-): AC 220V/110V live wire or DC 24V (-)
• AC 220V/110V (N) or DC 24V (+): AC 220V/110V neutral wire or DC 24V (+)
• HO: Normally-open relay for high alarm
• HC: Normally-closed relay for high alarm
• LO: Normally-open relay for low alarm
• LC: Normally-closed relay for low alarm
• COM: Common terminal

Communication

RS485 communication data and register address as follows:

PHM-PH8 pH Meter User Manual.pdf

Q1: What is the working principle of a pH meter?
A1: The pH meter works on the principle of a galvanic battery. The electromotive force between the two electrodes of the galvanic battery is based on Nernst's law, which is not only related to the properties of the electrodes, but also to the concentration of hydrogen ions in the solution. There is a the corresponding relationship between the electromotive force of the primary cell and the hydrogen ion concentration, and the negative logarithm of the hydrogen ion concentration is the pH value.

Q2: The same sample is measured on two pH meters at the same time, why are the readings inconsistent?
A2: Because the calibration conditions of the two pH meters are different (such as calibration done at different times), the measured values are different. Therefore, the pH meter should be calibrated at the same time with the same buffer, and then measured at the same time.

Q3: How do I know if the pH meter is accurate?
A3: Take three standard buffer solutions: pH 6.86, pH 4.00, pH 9.18 (preferably freshly prepared and at the same temperature), position calibration at pH 6.86, slope calibration at pH 4.00, and then test pH 9.18 to know the pH meter Is it accurate.

Tips: What types of pH meters are there?

Pen (miniature) pH meters and portable pH meters are generally used on-site by testing personnel. Portable pH meters and benchtop pH meters are common instruments with a wide range of measurements. The difference is that portable pH meters use DC power and can be brought to the job site. Laboratory pH meters have a wide measurement range, versatility and high measurement accuracy.

The industrial-grade online pH meter is more stable and reliable, has certain measurement accuracy, strong environmental adaptability, strong anti-interference ability, and also has functions such as analog output, digital communication, upper and lower limit alarms, and control functions. Measured at 20-30°C and pH 7, no temperature compensation is required. For measurements where the temperature is above 30°C or below 20°C and the pH is above 8 or below 6, compensation for temperature changes must be made.

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