pH Sensors / CS526
This product is no longer available. Some accessories, replacement parts, or services may still be available.
CS526 Digital ISFET pH Probe
Services Available
Repair Yes
Calibration Yes
Free Support Yes


The CS526 isolated pH probe makes reliable, accurate pH measurements in aqueous solutions. It can be submersed or inserted into tanks, pipelines, and open channels. This probe has a serial, TTL output that represents a 2 to 12 pH range.

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Benefits and Features

  • Innovative ISFET pH-sensing element
  • Easily cleaned
  • More rugged than the traditional glass electrode pH probes
  • Each sensor individually tested
  • Designed and manufactured under stringent quality control conditions in an ISO 9001 environment
  • CE compliant


Detailed Description

The CS526 uses SENTRON’s high-tech, ion sensitive field effect transistor (ISFET) semiconductor as its pH-sensitive element, and includes a silver/silver chloride– potassium chloride reference system. The CS526’s design allows it to be suitable for a variety of liquid pH-monitoring applications. The electronics are safely embedded in a durable PEEK body. Elimination of the glass bulb removes the possibility of broken glass, making the CS526 more rugged and safer to use.

Note: Campbell Scientific warranty does not cover a clogged reference diaphragm or improperly cleaned or maintained ISFET chip. (See the Maintenance section in the instruction manual for more information.)

This sensor requires the 5 V output on the data logger to be powered.. 


pH Range 2 to 12
Power Requirements 5 Vdc
Current Consumption 15 mA (maximum)
Accuracy ±0.2 pH (over 10° to 40°C)
Operating Temperature Range 10° to 40°C
  • Serial TTL logic
  • 2400 bps
  • 8 data bits
  • no parity
  • 1 stop bit
24 h Drift < 0.15 pH (after 15 min. soak in pH 7 at 25°C)
Allowed Water Pressure 0 to 700 kPa (0 to 101.5 psi)
Cable Type Three-twisted pair, 24 AWG cable with Santoprene jacket
Sensor Material Polyetheretherketone (PEEK)
Maximum Cable Length 100 m (328 ft)
Diameter 16 mm (0.63 in.)
Length 102 mm (4 in.)
Weight 318 g (11.2 oz) with 3.05 m (10 ft) cable


Please note: The following shows notable compatibility information. It is not a comprehensive list of all compatible products.

Data Loggers

Compatible Note
CR1000 (retired)
CR200X (retired)
CR206X (retired)
CR295X (retired)
CR3000 (retired)
CR5000 (retired)
CR9000X (retired)

FAQs for

Number of FAQs related to CS526: 15

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  1. The CR300 and CR310 dataloggers do not support TTL logic, which is what the CS526-L sensor uses. A TTL to RS-232 converter (supplied by the user) could be used, however.

  2. The source and the drain are two of the three electrodes contained within the ISFET chip, and they behave in much the same way. The third electrode in the ISFET chip, the gate, has an electrical field that influences the current that flows between the source and the drain. The electrical potential in the ISFET pH sensor is measured between the reference electrode and the source.

  3. An ISFET chip pH sensor has three main components:

    • ISFET chip—The ISFET chip is made of durable plastic and contains three electrodes: the source, the drain, and the gate. The gate is the ISFET chip’s only electrode that comes in contact with the sample solution.
    • Reference electrode—Inside the reference electrode’s membrane, there is a silver wire element submersed in an electrolyte solution. The reference electrode, as a whole, is submersed in the sample solution.
    • Reference junction—The reference junction is located at the end of the reference electrode by the sample solution. It interacts with both the reference electrode’s electrolyte solution and the sample solution to complete the electrical circuit.
  4. In an ISFET chip pH sensor, the chemical coating on the gate electrode can vary depending on the model and manufacturer of the pH sensor. Depending on which chemical coating is used and what elements are present in the sample solution, there may be some ion interference.

  5. The CS526-L pH sensor uses an ISFET chip instead of pH-sensitive glass, which is used for many other pH sensors. The ISFET chip is a transistor coated with a chemically sensitive material. One of the ISFET chip’s electrodes (the gate) and the reference electrode are submersed in the same sample solution. A circuit path is established between the two electrodes. The difference in electrical potential between the two electrodes is directly proportional to the sample solution’s pH. Thus, by measuring the electrical potential, the pH is measured.

  6. PolyEtherEtherKetone (PEEK) is a plastic material that has very good thermal stability and chemical resistance properties. This material was chosen for use in the manufacture of the CS526-L because of its natural resistance to organic acids (acetic, carbonic, citric, tartaric, etc.) and its hydrolysis resistance to fresh and saltwater.

  7. Silver is the best electrical conductor of all the metals because it has the lowest electrical resistance. The silver wire, coated in silver chloride, is relatively insensitive to changes in temperature. 

  8. A reference electrode can become contaminated when poisoning ions such as lead, iron, chrome, cyanide, or sulfide enter the reference electrode and react either with the silver wire or with the electrolyte solution.

    The contamination may not become apparent until the silver-chloride coating is completely dissolved and the electrical potential from the reference electrode has changed greatly. If this occurs, the reference electrode must be replaced.

  9. Cleaning and/or calibration may be required when the measurements are scattered, drifting occurs, or there is physical evidence of fouling. Measurements for pH must be monitored regularly to check for scattering. However, just because the results are scattered does not necessarily indicate the need for an adjustment. For example, there may be a change in the water source that causes the scattering. As a sensor ages, however, the scattering of the measured values tends to increase.

    To check the performance of a pH sensor, use it to measure a buffer solution in the correct range. If the value returned is within the specified range, the sensor does not need to be calibrated.

  10. Most Campbell Scientific sensors are available as an –L, which indicates a user-specified cable length. If a sensor is listed as an –LX model (where “X” is some other character), that sensor’s cable has a user-specified length, but it terminates with a specific connector for a unique system:

    • An –LC model has a user-specified cable length for connection to an ET107, CS110, or retired Metdata1.
    • An –LQ model has a user-specified cable length for connection to a RAWS-P weather station.

    If a sensor does not have an –L or other –LX designation after the main model number, the sensor has a set cable length. The cable length is listed at the end of the Description field in the product’s Ordering information. For example, the 034B-ET model has a description of “Met One Wind Set for ET Station, 67 inch Cable.” Products with a set cable length terminate, as a default, with pigtails.

    If a cable terminates with a special connector for a unique system, the end of the model number designates which system. For example, the 034B-ET model designates the sensor as a 034B for an ET107 system.

    • –ET models terminate with the connector for an ET107 weather station.
    • –ETM models terminate with the connector for an ET107 weather station, but they also include a special system mounting, which is often convenient when purchasing a replacement part.
    • –QD models terminate with the connector for a RAWS-F Quick Deployment Station.
    • –PW models terminate with the connector for a PWENC or pre-wired system.