Hach pHD Manual Básico Del Usuario página 16

6.1 Maintenance schedule
Table 3 shows the recommended schedule of maintenance tasks. Facility requirements and
operating conditions may increase the frequency of some tasks.
Maintenance task
Clean the sensor on page 16
Replace the salt bridge
Calibrate the sensor on page 10
6.2 Clean the sensor
Pre-requisite: Prepare a mild soap solution with a non-abrasive dishwashing detergent that does not
contain lanolin. Lanolin leaves a film on the electrode surface that can degrade the sensor
performance.
Examine the sensor periodically for debris and deposits. Clean the sensor when there is a buildup of
deposits or when performance has degraded.
1. Use a clean, soft cloth to remove loose debris from the end of the sensor. Rinse the sensor with
clean, warm water.
2. Soak the sensor for 2 to 3 minutes in the soap solution.
3. Use a soft bristle brush to scrub the entire measuring end of the sensor.
4. If debris remains, soak the measuring end of the sensor in a dilute acid solution such as < 5%
HCl for a maximum of 5 minutes.
5. Rinse the sensor with water and then return to the soap solution for 2 to 3 minutes.
6. Rinse the sensor with clean water.
Note: Sensors with antimony electrodes for HF applications may require additional cleaning. Contact technical
support.
Always calibrate the sensor after maintenance procedures are done.
6.3 Replace the salt bridge
Replace the salt bridge and the standard cell solution at 1 year intervals or when calibration fails after
the sensor has been cleaned.
Note: A video that shows how to replace the salt bridge is available on www.Hach.com. Go to the salt bridge
webpage and click the Video tab.
Items to collect:
• Adjustable crescent wrench
• Large tweezers
• Salt bridge
• Standard cell solution
3
• Gel powder , ⅛ teaspoon
1. Clean the sensor. Refer to
2. Replace the salt bridge and the standard cell solution. Refer to the illustrated steps that follow.
If the reservoir for the standard cell solution contains a gel (not usual), use a jet of water from a
water pik-type device to remove the old gel at illustrated step 2.
3
(Optional) Add gel powder to the standard cell solution if the process water is near the boiling
temperature. The gel powder decreases the evaporation rate of the standard cell solution.
16 English
Table 3 Maintenance schedule
on page 16
Clean the sensor
1 year
X
Set by regulatory agencies or experience
on page 16.
As necessary
X