Chlorine and pH Levels in Water Treatment Plant

The chlorine and pH level of water is extensively monitored at each stage of its treatment process. If the pH value or chlorine level deviates from its parameters, then a plant operator needs to take corrective action.

The Problem:
 

From time to time the pH and chlorine levels will fluctuate at each stage in the treatment process without actually being of significance or detrimental to the final product. A disadvantage of using an instrument connected to a single probe is that probe failure can occur and will lead to a false alarm. Additionally, this relies on a plant operator regularly checking the display to ensure parameters are not being exceeded.

The Solution:
 

Mantracourt's solution addresses the problems highlighted above by using pairs of dual input instruments acting as signal comparators, one for a pair of chlorine monitoring probes, and the other for pH monitoring probes. The instruments take the 4-20mA outputs from the probes as their inputs and electronically compares the values. The differences in the respective values are then displayed locally - engineering units (mg/l) are used for the chlorine and pH units for the pH probes.

When a discrepancy in the measured value between the two probes occurs, the signal output is frozen at the last valid reading. A user adjustable alarm is provided so that the plant controller will be notified in the event of a pre-set difference in reading from a pair of probes occurring. Additionally, the alarm is only initiated if the alarm threshold is exceeded for more than a user pre-set period of time.

A manual selector switch is included to allow the analogue signal from either of a pair of probes to directly control the process - in case of probe failure.

The system described above provides an excellent solution to pH and chlorine monitoring in water treatment plants. The main advantages are:

• Operators can see the probe readings and decide if they want to take action
• The alarm initiation is user definable
• The readings of two probes are compared

Products used in this application: