Tech Tips - Hach Hydromet

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Tech Tips

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Storage Tips

When Hydrolab equipment is not in use, most sensors must be kept moist to prevent damage. We recommend using pH 4.01 buffer as a storage medium for both long and short term storage. After performing a slope calibration with pH 4.01, rather than discarding the buffer, save it to use as a storage medium. Although calibration standards should never be reused for calibration, used pH 4.01 buffer will be fine to use as a storage medium. In the absence of pH 4.01 buffer, clean tap water is second best. If field water must be used, replace it with a recommended medium as soon as the instrument is back at the lab. Do not use deionized water or allow the storage medium to freeze.

Quality Control Checking of Calibrations

  1. General
    It is a good idea to check linearity on most sensors with a mid-range standard if at all possible. By doing so, you are assuring the accuracy of your calibration standards, the soundness of your calibration practices, and the proper function of your sonde's sensors.

    Remember to allow the sensor's readings to stabilize, AND to allow for temperature readings to stabilize as well, before calibrating.

  2. LDO
    Unlike the older polar-graphic 'Clark-Cell' DO sensors, the LDO sensor will accept all barometric pressures values as valid when calibrating. As a quality control measure, the 'Scale Factor' should be checked after performing your calibration. The Scale Factor value should always fall within a value of 0.5 to 1.5. Outside of this range could mean, the LDO cap may be in need of replacement. Or, the actual barometric pressure doesn't concur with the calibrated value. Or, the sensor may be experiencing a malfunction.

    To access the LDO sensor's Scale Factor value simply:
    1. Establish PC communications with your instrument via Hydras 3 LT.
    2. Click on the 'Terminal Mode' button.
    3. Log-in to Security Level 3.
    4. Navigate to: Set-up, , Sensors, , LDO, , LDO:%Sat,

  3. pH

  4. Although mid-range buffers exist, they are not common in most labs. However, properly functioning pH probes should read outside of their calibrated slope with reasonable accuracy. In other words, if you perform a slope calibration with pH 7 and pH 10 buffers, the sensor should read a pH 4 buffer between 3.8 to 4.2 pH units. Series 5 sondes may be set-up for a 3 point calibration as well.

  5. Conductivity

  6. Series 5 sondes may be set-up for a 2 or 4 point calibration for measuring specific conductivity. Most people find a 2 point calibration satisfactory along as the calibration 'brackets' their sampling environment. In other words, if your sampling is typically around 2 mS/cm, you calibrate using 0.0 (air) and a standard as high as 12.856 mS/cm. A good mid-range standard for quality assurance checking would be 100 uS/cm, 500 uS/cm, or 1.412 mS/cm.

    By factory default, the sonde has been set-up for automatic temperature compensation. Therefore, performing a temperature compensated calibration should not be performed. Just simply enter the value printed on the standard's label regardless of temperature.

  7. TDG
    After calibrating and reinstalling a new membrane, ample time should be allowed for the membrane to relax. As a simple test to ensure your TDG sensor is responsive is use club soda. TDG readings should immediately rise when the club soda is added to the calibration cup. As the CO2 levels fall, so should your TDG readings.



  8. View the Hydrolab Maintenance Checklist. GO>

    Contact Us


    Hach Hydromet Product Repair
    Loveland Service Center
    5600 Lindbergh Drive
    North Dock


    Tel: 800-949-3766 opt. 2
    Fax: 970-461-3921
    Support Form




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