How to Set Practical Water Quality Alarm Thresholds Malaysia
How to Set Practical Water Quality Alarm Thresholds Malaysia
Content
An online water-quality system can measure continuously and generate alarms when a parameter moves outside a defined limit.
However, an alarm is only useful when its threshold reflects the actual process, instrument performance and operational response.
If the limit is too tight, normal fluctuations may generate repeated false alarms. If it is too wide, the system may fail to warn operators before the process or discharge becomes unacceptable.
Water and wastewater facilities in Malaysia should set alarm thresholds using baseline data, process requirements and confirmed response procedures—not simply copy the instrument’s factory default settings.
What Is a Water Quality Alarm Threshold?
An alarm threshold is a defined value that triggers a warning or action.
Examples include:
High pH alarm
Low pH alarm
Low dissolved-oxygen alarm
High turbidity alarm
High conductivity alarm
High temperature alarm
Abnormal ORP alarm
Rapid rate-of-change alarm
Sensor-failure alarm
A threshold may activate:
A local buzzer or warning light
A message to an operator
A SCADA notification
A control relay
A shutdown procedure
Automatic chemical dosing
Increased aeration
Diversion of wastewater to a holding tank
The selected response should match the seriousness and reliability of the alarm.
Why Factory Default Alarms May Be Unsuitable
Instrument defaults are normally general settings. They do not know:
The facility’s normal water quality
Local process variation
Regulatory discharge requirements
Seasonal changes
Production schedules
Sensor location
Treatment-system response time
Consequences of exceeding the limit
A default threshold can be a starting reference, but it should not automatically become the facility’s operating alarm.
Compliance Limit vs Operating Alarm
A regulatory or discharge limit and an operating alarm serve different purposes.
Compliance Limit
This is the maximum or minimum value allowed under the relevant requirement, permit or standard.
Operating Alarm
This warns the operator early enough to investigate and correct the process before the compliance limit is reached.
Setting the alarm exactly at the discharge limit may provide insufficient reaction time.
For example, a facility may use:
An early-warning level
A high alarm
A high-high alarm requiring urgent action
The actual values must be established according to the process, permit and risk.
Step 1: Define the Monitoring Objective
Before setting a limit, determine why the parameter is being measured.
Possible objectives include:
Regulatory compliance
Process control
Equipment protection
Drinking-water quality
Cooling-water management
Aquaculture protection
Contamination detection
Early warning
Chemical-dosing control
Product-quality protection
The same pH or conductivity sensor may require different alarm settings in different applications.
Step 2: Confirm the Measurement Location
Thresholds are meaningful only when the sensor location is understood.
A sensor may be installed:
At the raw-water intake
Inside an equalisation tank
In an aeration basin
After chemical dosing
After filtration
At the final discharge point
In a cooling-water return line
In a fish pond
In a river or drainage channel
The normal range at the influent may be completely different from the normal range at the final outlet.
Do not apply one threshold to every measurement point.
Step 3: Establish the Normal Baseline
Collect sufficient data under normal operating conditions.
The baseline should cover:
Different production loads
Day and night
Weekdays and weekends
Wet and dry weather
Startup and shutdown
Cleaning cycles
Chemical dosing
Seasonal or raw-water changes
Planned maintenance
A few readings from one quiet day are not enough to define normal behaviour.
Step 4: Review Data Quality
Before calculating limits, remove or investigate data affected by:
Sensor maintenance
Calibration
Power failure
Communication loss
Probe removal
Air bubbles
Empty pipe
Fouling
Sample-flow interruption
Known abnormal testing conditions
If poor-quality data is treated as normal variation, the resulting threshold may become too wide.
Step 5: Understand Normal Variability
Review:
Typical value
Minimum and maximum
Daily pattern
Rate of change
Process-cycle pattern
Relationship with production
Relationship with temperature and flow
A parameter that naturally changes rapidly may need a different alarm strategy from one that normally remains stable.
Step 6: Set More Than One Alarm Level
A staged system is often more practical than one single alarm.
Advisory or Early Warning
Signals that the parameter is moving away from normal.
Possible response:
Review the trend
Check the process condition
Prepare for inspection
High or Low Alarm
Indicates that operator action is required.
Possible response:
Verify the sensor
Check treatment equipment
Take a portable measurement
Adjust the process
High-High or Low-Low Alarm
Indicates a serious condition requiring immediate escalation.
Possible response:
Stop or divert discharge
Activate standby equipment
Notify responsible personnel
Collect a confirmation sample
Begin the emergency procedure
The terminology and response should be defined in the site’s operating procedure.
Step 7: Use Delay and Persistence Settings
A sensor may briefly cross a limit because of:
Electrical noise
Air bubbles
Splashing
A short process transition
Temporary sample interruption
An alarm delay or persistence requirement can reduce nuisance alarms.
For example, an alarm may activate only if the value remains outside the limit for a defined period.
The delay must not be so long that a genuine event is missed.
Fast-moving or high-risk processes may require a shorter delay than stable, low-risk systems.
Step 8: Apply Hysteresis
Without hysteresis, an alarm may repeatedly turn on and off when the reading fluctuates close to the threshold.
Hysteresis creates a separate reset value.
For example:
High alarm activates at the selected upper threshold
Alarm clears only after the reading falls sufficiently below it
This reduces alarm chattering and repeated notifications.
Step 9: Consider Rate-of-Change Alarms
Some contamination events may be important even when the absolute value has not yet crossed the final threshold.
A rate-of-change alarm can identify:
Sudden conductivity increase
Rapid pH shift
Fast turbidity rise
Sudden DO decline
Unexpected temperature change
This method is useful when a normally stable parameter changes quickly.
Rate-of-change alarms should be tested carefully because maintenance, cleaning or process switching may also create rapid changes.
Parameter-Specific Considerations
pH Alarms
pH alarms may be used for:
Neutralisation control
Chemical dosing
Biological-process protection
Final-discharge monitoring
Consider:
Probe response time
Temperature
Chemical mixing
Sensor location
Calibration condition
Process-control delay
A pH sensor installed too close to the chemical injection point may respond to unmixed chemical and generate an unrepresentative alarm.
Dissolved-Oxygen Alarms
DO alarms may indicate:
Loss of aeration
Blower failure
Excessive oxygen demand
Process overload
Sensor fouling
Mixer failure
DO thresholds should account for:
Treatment process
Temperature
Tank location
Operating load
Aerobic or anoxic zone
Biological requirements
A low DO alarm in an aerobic tank has a different meaning from the same reading in an anoxic tank.
Turbidity Alarms
High turbidity may indicate:
Filter breakthrough
Clarifier carryover
Coagulation failure
Sediment disturbance
High suspended solids
Air bubbles
Dirty optics
The alarm procedure should include sensor inspection and sample confirmation because bubbles and optical fouling can produce false high readings.
Conductivity Alarms
Conductivity alarms may identify:
Chemical discharge
Brine contamination
Cooling-water concentration
Reverse-osmosis breakthrough
Dilution
Changes in raw water
Conductivity is strongly influenced by temperature. Confirm how the instrument applies temperature compensation.
ORP Alarms
ORP is normally more useful as a process trend than as a universal water-quality limit.
Its interpretation depends on:
Wastewater composition
Biological activity
Chemical dosing
pH
Electrode condition
Aerobic, anoxic or anaerobic operation
Site-specific baseline data is particularly important before establishing ORP alarms.
Temperature Alarms
Temperature alarms may protect:
Biological treatment
Aquaculture
Equipment
Membranes
Process chemistry
Cooling-water systems
The sensor location and normal daily variation should be understood before selecting limits.
Step 10: Define the Alarm Response
Every alarm should answer four questions:
Who receives the alarm?
How quickly must they respond?
What must they check?
Who has authority to adjust or stop the process?
A practical response checklist may include:
Confirm the time and location
Review the recent trend
Inspect the online sensor
Check calibration or maintenance status
Measure with a portable instrument
Collect a sample if necessary
Inspect pumps, blowers or dosing equipment
Review recent production changes
Record the action taken
Escalate if the condition continues
An alarm without a defined response may become only another ignored notification.
Verifying an Alarm with a Portable Meter
When an alarm activates:
Bring a calibrated portable instrument to the measurement point.
Measure at the same location and depth.
Allow the reading to stabilise.
Record temperature and operating conditions.
Compare both results.
Inspect the online probe for fouling or damage.
Take a laboratory sample if confirmation is required.
If the portable and online readings differ, do not automatically assume that the online sensor is faulty. Check whether both measurements were made under identical conditions.
Managing False Alarms
Frequent false alarms can cause operators to ignore genuine warnings.
Investigate whether false alarms are caused by:
Incorrect threshold
Sensor fouling
Poor installation
Air bubbles
Electrical interference
Communication failure
Normal process cycles
Insufficient delay
Lack of hysteresis
Unstable sample flow
Calibration drift
The solution may involve instrument maintenance, installation improvement or alarm-logic adjustment.
Review Thresholds Regularly
Alarm thresholds should be reviewed after:
Process modification
Increased production
New wastewater source
Sensor replacement
Treatment-equipment upgrade
Regulatory change
Repeated alarms
Significant seasonal variation
Change in chemical programme
The review should be documented so that future operators understand why each threshold was selected.
Portable and Online Instruments Work Together
A reliable monitoring programme normally combines:
Online sensors for continuous detection
Portable meters for field verification
Laboratory testing for confirmation
Maintenance records
Defined alarm responses
Regular threshold review
Continuous data is valuable only when the sensors and alarm logic are maintained properly.
Water-Quality Instruments from MTM Precision
MTM Precision supplies water-quality instruments for process checks, troubleshooting and verification of online monitoring systems in Malaysia.
Available categories include:
Portable dissolved-oxygen meters
Portable and benchtop pH meters
ORP meters
EC and TDS meters
Turbidity meters
Suspended-solids meters
Temperature meters
Multi-parameter instruments
Calibration buffers and standard solutions
Relevant available models include:
QiWei 70A dissolved-oxygen meter
QiWei PH220W portable pH meter
QiWei PHS-25 benchtop pH meter
WGZ-1B turbidity meter
PAL-401 suspended-solids meter
Portable instruments can support alarm investigation by confirming the actual condition at the sensor location.
Contact MTM Precision
MTM Precision Sdn. Bhd. (744811-A)
Tel: 03-8080 7172
WhatsApp: +6016-660 7346
Email: mtmpre@yahoo.com / enquiry@mtmpre.com.my
Website: www.mtmpre.com.my
Visit our Puchong Showroom & Service Centre for water-quality instrument selection, product demonstration and technical support.
Operating hours: Monday to Friday, 9:00 AM–6:00 PM.
20 Sep 2026
