Electro-Chemical Devices (ECD) HYDRA Ammonium - Manual (Page 34)

Page 26 HYDRA NH
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5.0 MAINTENANCE
5.1 MAINTENANCE SCHEDULE
The HYDRA sensor requires little maintenance since most of the required cleaning is accomplished by
the Air Blast Spray Cleaner. Determining the proper cleaning cycle and duration for the application will
keep the front end of the sensor clean for extended periods but weekly inspection of the sensing end is
recommended.
Weekly calibration checks versus a grab sample are recommended to minimize any drift in the sensor.
Once the stability of the sensor has been established in the process, the time between calibration
checks can be adjusted. A calibration check must occur at least once per month.
The HYDRA should be checked monthly in calibration solutions for proper span of both the ammonium
and potassium electrodes. The electrodes start life with a span in the 55 mV/decade range and drop off
into the 40 mV/decade range as they age. Readings below 40 mV/decade indicate the electrode should
be replaced. Depending on the characteristics of the water being measured the Ion Selective electrodes
should last 3-6 months.
5.2 CLEANING THE SENSOR
The HYDRA sensor can be rinsed with water and wiped with a soft brush or cloth to remove most
coatings. DO NOT clean the potassium or ammonium ion electrodes with a stiff brush or vigorous wiping
as the sensing membrane is easily torn. DO NOT use strong detergent solutions or Spray Glass cleaners
to clean the sensor, the potassium and ammonium electrodes will be irreparably harmed. The sensor
can be soaked in dilute HCl, 2-3%, for 15 minutes to help remove stubborn coatings. Use a weak
detergent solution, a couple of drops detergent per liter of water, to remove any oily coatings. The pH
electrode and HYDRA housing can be cleaned in a more rigorous manner since the plastic body and glass
membrane are more durable than the Ion Selective Electrodes.
5.3 REPLACING THE ELECTRODES
The three electrodes, Ammonium, Potassium and pH are easily replaceable by simply removing the
electrode guard, screwing out the old sensor and screwing in the new one using the supplied installation
tool. Make sure no water gets inside the sensor when removing the electrodes. Water will cause the
internal electronics to fail. If the electronics are compromised the HYDRA sensor must be replaced.
The potassium and ammonium electrodes are PVC membrane combination electrodes (indicator
electrode and reference electrode in one body) and the pH electrode is a glass membrane combination
electrode.
Apply a thin film of o-ring lubricant to the o-rings on the electrode before installing it into the sensor
housing. Use the supplied electrode installation tool to remove or install electrodes into the sensor. The
use of pliers or other tools is not recommended as they may crack the electrode housing.