KPH601 Online PH Sensor Signal Output: RS-485 (Modbus/RTU Protocol) 

1.Signal processing and environmental influences

Calibration and control The electrode is characterized by its zero point and its slope. In addition to the two-point calibration, other methods exist which can monitor the performance of the electrode. For instance, a so called one-point calibration may be performed, provided that the slope remains constant. If a process sample is taken instead of using the buffer solution, and its pH value is measured in the lab, the electrode does not have to be removed from the process. The pH transmitter can be set using the pH value obtained for the sample in the laboratory. However, it has to be taken into consideration that the pH value of the measured solution is a function of different parameters such as temperature, dissolved C02 level, completion of reaction, etc. A second possibility for controlling the system is to determine both the zero point and the slope in the laboratory and subsequently enter the values into the pH transmitter.

Temperature compensation Automatic temperature compensation is generally used in industry, except when both calibration and pH measurement occur at a constant temperature. If the process temperature does not differ from room temperature by more than 10°C, temperature compensation is often not necessary, since the measuring error is less than 0.15 pH units.

Accuracy and reproducibility of measuring values The main differences between pH measurement in the laboratory and in industry are the frequency of calibration and the accessibility of the pH assembly. The accuracy and reproducibility of the measured values depend basically on the frequency of calibration and maintenance of the electrode. 

Environment Environmental influences act mainly on the cable and on the pH transmitter. The most important factors are the surrounding temperature, relative humidity, and electromagnetic fields. Hence, in industry protection class IP65 should be observed, as well as a robust design. In industry different hazardous areas may exist. The pH transmitter has to be designed according to the requirements for each safety zone.

Cable Since the signals are high impedance, long cables are susceptible to disturbances. At a cable length of over 10 meters a preamplifier is desirable; at a length of over 20 meters, indispensable. A coaxial cable is used as an electrode connection cable. In the case of strong electromagnetic disturbances (caused, for example, by motors) it is wise to use a triaxial cable ( a coaxial cable with an additional shield), for which a correct grounding of the outer shield is needed. The outer shield should be grounded only in one place.

Signal interpretation For signal conditioning, transmitters are galvanically isolated between input and output to prevent ground loops. This helps to avoid disturbances caused by potential differences between the transmitter ground and the ground potentials in the vessel, reactor, or in the pipe-line. These ground currents will otherwise flow through the reference electrode and appear as a signal error or even destroy the reference system. These kinds of disturbances are eliminated without exception through galvanic isolation. Digital measurement systems The development over the past decade of digital process analytical measurement systems for pH and other parameters,, has brought about significant improvements to sensor operations. These include digital transmission of the measurement signal from the sensor to the transmitter. This eliminates the influence of the aforementioned environmental factors and cable length on signal integrity.

2.Technical Specifications

3.Dimensional Drawing

Note:The sensor connector is M16-5 core waterproof joint male head.

4.Installation

Note: The sensor should not be installed upside down or horizontally when installed, at least at an angle of 15 degrees or more.

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