High Level Alarms or Low Level Alarms (Transmitter)

When to use this guide

Use this guide when:

A High level or Low level alarm based on a level transmitter is active
The tank level appears implausible compared to expected operation
Level alarms occur repeatedly during normal operation, BW, or refilling
The alarm severity does not seem appropriate for the situation
A customer refers to a specific alarm ID together with high or low tank level

Scope and boundaries

This guide applies to levels measured by analog transmitters.

It focuses on:

process behavior
setpoints
scaling
alarm limits and severity

It does not cover:

digital level switches
discrete level alarms used in CIP or chemical modules
transmitter signal faults (wiring, IO, 4–20 mA loss)

Preconditions and safety

Before starting troubleshooting:

The system should normally be in STOP state for checks and adjustments
Observation of level behavior may be done during live operation
Electrical troubleshooting shall only be performed by personnel with relevant competence
Always follow site-specific safety procedures

Important concept (read first)

On the majority of CF systems, the Permeate / BW tank is an actively controlled tank.

The HMI setpoint “Permeate tank level [%]” is used as a control reference
It regulates the pump discharging permeate downstream
The level is PID-controlled, not static

This means:

The tank level will naturally move around the setpoint
Small oscillations, overshoot, or undershoot are expected behavior
Level alarms must always be interpreted in the context of:
- current operating mode
- production settings (feed, recovery)
- BW activity

A level alarm does not automatically indicate a fault.

Step-by-step troubleshooting procedure

1. Understand which alarm you are dealing with

Confirm whether the alarm is:

High level (transmitter)
Low level (transmitter)

Both are process alarms, not safety switches.

As a general guideline:

Low level is typically critical, as it protects pumps and operation
70-85% is a normal level setpoint to aim for.
High level is often non-critical, especially if a physical high-level switch exists in the same tank

Always verify the configured alarm severity on the HMI.

2. Check whether the alarm fits the current operation

Before adjusting anything, ask:

Did the alarm occur:
- after BW?
- during extensive BW?
- after a change in feed setpoint or recovery?
Is the tank currently being:
- actively filled?
- actively drained?
- regulated around a setpoint?

Many level alarms occur during transient but expected conditions.

3. Verify level transmitter scaling (always relevant)

Scaling must be considered regardless of whether the alarm is high or low.

A level reading can be:

perfectly scaled
functionally acceptable
or clearly non-functional

The goal here is plausibility, not perfection.

Practical scaling plausibility check

A simple and effective method:

Set the permeate tank level setpoint to approx. 50 %
Stop the system
Verify that the liquid level is roughly:
- half the effective tank height
- measured from the bottom of the transmitter
Let the tank fill to approx. 75 % and verify plausibility again
Finally, let the tank approach 100 % (or the physical upper limit being the high level switch) and verify that the reading still makes sense relative to the tank geometry

The transmitter should behave monotonically and reasonably across the range.

Also inspect the physical condition of the transmitter:

buildup
damage
abnormal response
placement - if submergable it needs to be close to the bottom of the tank.

4. Platform-specific note on scaling

MK8 and newer CF systems
- Level transmitter scaling can be adjusted from the HMI
- Scaling errors may therefore originate from previous adjustments
MK6 systems
- Scaling cannot be adjusted from the HMI
- If scaling is clearly off (non-functional or implausible), LiqTech must be contacted
- Provide:
  - observed level values
  - approximate physical level
  - tank geometry
  - when the alarm occurs

There is an important difference between:

perfectly calibrated
functionally acceptable
non-functional scaling

Only the last requires immediate escalation.

5. Review alarm limits and setpoints together

Level behavior is defined by three interacting elements:

the PID setpoint (e.g. permeate tank level [%])
the level transmitter alarm limits
the physical tank volume

Verify that:

High and low alarm limits are not too close to the normal operating range
Normal refilling after BW does not unintentionally trigger high level alarms
Extensive BW does not unintentionally trigger low level alarms

6. Handling repeated high level alarms

If repeated high level transmitter alarms are observed:

A small reduction of the permeate tank level setpoint may be considered
This is often sufficient when:
- production parameters are changed rapidly
- feed setpoint or recovery is increased
- the system is installed in a marine environment with significant motion

This is a drift optimization, not a fault correction.

7. Handling repeated low level alarms

If repeated low level transmitter alarms are observed:

Consider whether BW volume or BW duration is excessive
Verify whether permeate production is sufficient to refill the tank
If practice allows, the tank level setpoint may be increased slightly

The most common root cause is:

long or heavy BW cycles
sometimes combined with insufficient permeate production

Example – Permeate tank level alarms and operating setpoints

High and low level alarms on the permeate tank are often a result of normal operating behavior, not incorrect alarm configuration.

In typical operation:

The Permeate tank level [%] defines the normal operating level (Setpoint)
Minimum level to start BW [%] is set lower than the normal operating level (Setpoint)
A Low level alarm is set to trigger before the tank becomes empty (Alarm Setting)
A High level alarm is set above the normal operating level (Alarm Setting)
A High level switch acts as the final safety layer

If the operating setpoints are poorly aligned, level alarms may occur even though the system is functioning as intended.

Common root causes

Most common

Operation setpoint level set to close to Alarm limits or vice versa.
Incorrect or poorly aligned level transmitter scaling

Also common

Production changes (feed, recovery)
Extensive BW consuming more volume than expected
Setpoint not adapted to actual operating conditions (e.g. high seas on marine systems)

These are process configuration topics, not hardware failures.

When to contact LiqTech

Contact LiqTech if:

Level transmitter scaling on an MK6 system appears non-functional
Level readings are implausible across the entire range
Repeated alarms cannot be rationalized by operation, BW, or setpoints

When contacting LiqTech, clearly describe:

what level is shown
what physical level is observed
when alarms occur
what has already been verified

Alarm ID references (examples)

The following alarm IDs are examples of analog level alarms this guide applies to.
They are provided as recognition aids for support agents.
Other alarm IDs with similar texts may exist.

MK6 – Level Transmitters

Alarm ID 34 – Level transmitter (permeate / tank related)
Alarm ID 131 – Level transmitter (permeate tank variant)
Alarm ID 197 – Level transmitter (concentrate tank)
Alarm ID 204 – Level transmitter (reject tank)
Alarm ID 223 – Level transmitter (precipitation tank)

These alarms may represent high or low level conditions, depending on configuration.

MK8 / newer systems

Level alarms are typically referenced as:

Permeate tank high level
Permeate tank low level
Tank level high / low

Alarm numbering and naming may vary by project and configuration.

High Level Alarms or Low Level Alarms (Transmitter) – Initial Troubleshooting

This guide describes a practical, field-proven approach for troubleshooting analog level alarms based on level transmitters on LiqTech Crossflow (CF) systems. It focuses on process behavior, setpoints, scaling, and alarm configuration rather than signal or hardware faults.