Emerson Rosemount FCL, Reference Manual

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8.3 pH sensor
8.3.1 pH sensor maintenance
When used in clean water, the pH sensor requires little maintenance.
Generally, the sensor needs maintenance when the response becomes sluggish or noisy.
In clean water, the typical cleaning frequency is once a month. In water containing large
amounts of suspended solids, for example, open recirculating cooling water, cleaning
frequency will be substantially greater.
8.3.2 Cleaning the sensor
Complete the following steps to clean the pH sensor.
Procedure
1. Remove soft deposits by rinsing with a stream of water from a wash bottle.
2. If the sensor becomes coated with rust, dissolve the rust by soaking the sensor in
dilute citric acid (dissolve 5 grams of citric acid crystals in 100 mL of water) for no
longer than thirty minutes at room temperature.
3. Rinse the sensor thoroughly with water and soak in pH buffer for several hours.
4. Recalibrate the sensor in buffers before returning it to service.
8.3.3 Other maintenance
The 3900VP-02-10 sensor supplied with the Rosemount FCL-02 is disposable. It has no
replaceable parts.
8.4 Constant head flow controller
8.4.1 General head flow controller information
After a period of time, deposits may accumulate in the constant head overflow chamber
and in the tubing leading to the flow cell(s). Deposits increase the resistance to flow and
cause the flow to gradually decrease. Loss of flow may ultimately have an impact on the
sensor performance.
The flow controller is designed to provide about 2 gal/hr (120 mL/min) flow. Loss of flow to
about 1 gal/hr (60 mL/min) causes about a 5% decrease in chlorine sensor output.
Loss of flow has almost no effect on pH sensor performance other than to increase the
overall response time.
Reference Manual Maintenance
00809-0100-3412 May 2019
Rosemount FCL 1056 81