6561FG Flat Glass pH Sensor

6-Series Legacy Sondes

View YSI 6-Series water quality sondes being used in a variety of water environments for long-term underwater monitoring and spot sampling.

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Simple, accurate pH measurement in sensors designed for minimal maintenance in sampling, profiling, and long-term monitoring applications.

This sensor must be installed into a 6600EDS V2 sonde to function. Does not function on its own.

  • Overview

    YSI pH and pH/ORP sensors have been carefully designed to perform under all ionic strength conditions, from seawater with a conductivity of 53,000 μS/cm, to "average" freshwater lakes and rivers with conductivities of 200 to 1500 μS/cm, to pure mountain streams with conductivities as low as 15 μS/cm, which has historically been the most difficult medium with respect to accuracy, quick response to pH changes, and minimal flow dependence.

    6561FG Flat Glass pH Sensor:
    The YSI 6561FG pH sensor features a 'long-life' sealed gel reference, eliminating the need to refill.  Produces unattended pH readings in high-fouling environments on 6600EDS sondes.


    • Wipeable by 6600EDS sonde brush.
    • Glass is well-protected


    • Can produce jumpy readings when touched or near source of static interference
    • Not ideal for lab use.

    Sensor is available for use on the following sonde:

    • 6600EDS V2 only

    General Specifications:
    Range: 0 to 14 units
    Resolution: 0.01 unit
    Accuracy: ±0.2 unit

    U.S. EPA ETV

  • Specifications
    Depth / Pressure Rating / Limit 60 m
    Equipment used with 600QS, All except 600R, 6000, 600LS, 600OMS
    Medium Fresh and Salt Water
    Monitoring Yes
    Parameters Measured pH
    Sampling Yes
    User Calibratable Yes
    User Replaceable Yes
    Warranty 1 year

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