WTW FCML 412 N / FCML 412 M12 pH-Independent Sensor for Free Chlorine

1.1 Construction

The diagram shows the construction of the FCML 412 sensors. Key components include:

• 1. Connection: PG7 screw fitting for FCML 412 N; Flange connector for the ADA CL/IDS adapter for FCML 412 M12.
• 2. Shaft
• 3. Auxiliary Electrode
• 4. Electrode Finger
• 5. O-Ring: 14 x 1.8
• 6. Reference Electrode
• 7. Measuring Electrode
• 8. Valve Opening: Located behind the hose ring.
• 9. Membrane Cap
• 10. Membrane Holder
• 11. Membrane Disc

The sensor's special construction (potentiostatic 3-electrode system) measures the total free chlorine (sum of gaseous dissolved chlorine, hypochlorous acid, and hypochlorite) as well as chlorine bound to isocyanuric acid. The sensor is characterized by significantly reduced pH dependency. It features integrated measuring electronics and provides a temperature-compensated measurement signal. No zero point adjustment is required. Regular calibration is performed by comparison with the photometric DPD method according to DIN 38408.

1.2 Electrical Connection

• FCML 412 N: Connects via a two-wire connection to the transmitter (e.g., MULTILINE 1000). The two lines supply power from the transmitter and transmit the measurement signal (4-20 mA current signal).
• FCML 412 M12: Features an M12 flange connector for connection to the ADA CL/IDS adapter (see section 5.4). The ADA CL/IDS adapter connects the sensor to the MIQ/IDS module of the IQ Sensor Net. Power supply and signal transmission occur via the ADA CL/IDS adapter.

Apart from the different electrical connection, all FCML 412 sensors are identical.

2.1 Safety Information

This operating manual contains important information for the safe operation of the product. Read this manual thoroughly and familiarize yourself with the product before putting it into operation or working with it. Keep the manual readily available for reference.

Important safety notices are highlighted in this manual. They are indicated by a warning symbol (triangle) on the left margin. The signal word (e.g., "CAUTION") indicates the severity of the hazard:

• WARNING: Indicates a hazardous situation that can lead to severe (irreversible) injury or death if the safety notice is not followed.
• CAUTION: Indicates a hazardous situation that can lead to minor (reversible) injury if the safety notice is not followed.
• NOTE: Indicates potential material damage that can occur if the specified measures are not followed.

Product Safety Labels: Observe all labels, warning signs, and safety symbols on the product. A warning symbol (triangle) without text refers to safety information in this operating manual.

Other Documents with Safety Information: The following documents contain additional information that you should observe for your safety when working with a measurement system:

• Operating manuals for other components of the FCML 412 N, FCML 412 system (power supplies, controllers, accessories).
• Safety data sheets for calibration and maintenance materials (e.g., cleaning solutions).

2.2 Safe Operation

3.1 Scope of Delivery

• Sensor FCML 412 with membrane cap M48 (Sensor FCML 412 N or Sensor FCML 412 M12)
• Dropper bottle with 100 ml electrolyte solution ELY-FCML 412 N
• Grinding paper
• Operating manual

3.2 Filling the Membrane Cap with Electrolyte Solution

NOTE: Risk of damage to the sensor from improper handling. Do not touch the electrode finger with your fingers. Do not press the membrane disc. Do not unscrew the membrane holder.

The membrane cap is delivered loosely screwed onto the shaft without electrolyte filling. To commission, fill the membrane head as follows:

1. Unscrew the membrane cap from the electrode shaft. Place the membrane cap on a clean (non-absorbent) surface.
2. Cut the tip of the dropper bottle until the opening is visible, and fill the membrane cap to the brim with electrolyte solution, ensuring no air bubbles.
3. Lift the hose ring of the membrane cap, which seals the valve opening, to the side so that the valve opening is exposed (see diagram). Hold the sensor shaft vertically and place it onto the filled membrane cap. Electrolyte solution will run out over the top edge of the membrane cap. Then screw the electrode shaft into the membrane cap. First, turn counter-clockwise until the thread engages, then turn clockwise slowly until it stops, ensuring no gap remains between the sensor shaft and the membrane cap.

Diagram: Shows parts 1 (Valve opening) and 2 (Hose ring).

NOTE: Overpressure in the membrane cap can destroy the membrane disc. Ensure the valve opening is not accidentally closed with fingers. Excess electrolyte solution must be able to escape freely at all times. Screw slowly to avoid creating back pressure.

4. Using a blunt object, slide the hose ring over the valve opening and seat it evenly in the groove.
5. Rinse off any adhering electrolyte solution with water.

3.3 Electrical Connection

For the connection of the FCML 412 N sensor to the transmitter or MIQ/IDS module, please refer to the transmitter's operating manual. For the connection of the FCML 412 M12 sensor to the MIQ/IDS module, please refer to the MIQ/IDS module's operating manual.

3.4 Installation in Flow Cell D-CL

The D-CL flow cell is optimized for the FCML 412 N chlorine sensors.

ℹ️ The position in the flow cell significantly influences the flow and thus the sensor's measurement function. Position the sensor carefully as described below.

Proceed with installation as follows:

1. Slide the black O-ring, then the PVC sliding ring over the sensor.
2. Unscrew the flow cell's screw fitting.
3. Insert the sensor without the connected cable into the flow cell.
4. Slide the flow cell's screw fitting over the sensor.
5. Screw the flow cell's screw fitting onto the flow cell.

Diagram: Shows dimensions and parts for flow cell D-CL installation. Key labels:

• 1. Top edge of union nut
• 2. Above the center of the inlet opening
• 3. Lower edge of groove
• 4. Top edge of sensor

Step 6: Reconnect the sensor connection cable to the sensor.

NOTE: During commissioning, always open the inlet slowly. A strong surge of pressure can destroy the membrane.

3.5 Installation in Flow Cell D 19

The D 19 flow cell is optimized for the FCML 412 M12 chlorine sensor. The FCML 412 M12 sensor has a marking on its shaft for optimal installation in the D 19 flow cell.

ℹ️ The position in the flow cell significantly influences the flow and thus the sensor's measurement function. Position the sensor carefully as described below.

Proceed with installation as follows:

1. Connect and securely screw the ADA CL/IDS adapter to the M12 flange connector.
2. Loosely slide the flow cell's union nut onto the sensor.
3. Slide the sensor with the union nut into the flow cell.

Diagram: Shows sensor and flow cell parts. Key labels: 1. Marking on FCML 412 M12, 2. Top edge of union nut, 3. Outlet opening, 4. Inlet opening.

4. Align the sensor's marking (1) with the top edge (2) of the union nut.
5. Tighten the union nut by hand.
6. Further tighten the union nut by about a quarter turn using the M32 mounting wrench. Ensure the sensor is seated securely, as it could be pushed out of the flow cell by pressure.

NOTE: During commissioning, always open the inlet slowly. A strong surge of pressure can destroy the membrane.

The M32 mounting wrench is available as an accessory (see section 5.4 MAINTENANCE MATERIALS AND SPARE PARTS).

4.1 Polarization

After each refilling, the sensor must be polarized. Immerse the connected sensor, supplied with operating voltage, in a well-stirred chlorine solution with at least 5 mg/l chlorine for one hour. Then transfer the sensor to the application (measurement position). After an acclimatization period of approximately 20 minutes, the sensor can be calibrated. Recalibration should occur after approximately one day.

ℹ️ The sensor filled with electrolyte must not dry out and must be permanently supplied with electrical voltage. Otherwise, the properties of the membrane cap, electrode finger, and electrolyte will be altered (partially irreparably). The sensor must only be stored in an unfilled state (see section 5.3 STORAGE).

4.2 Sensor / Analytics Control

Calibration with DPD-1 Method: The chlorine sensor has a linear characteristic. Calibration is a single-point calibration. The calibration value (target value) is usually determined photometrically. A common method is the DPD method for free chlorine. Photometers and test kits can be found in the WTW catalog or online. Refer to the transmitter's operating manual for the exact calibration procedure.

4.3 Chlorine Measurement with FCML 412

The FCML 412 chlorine sensor detects inorganic chlorine compounds dissolved in water. Measurement values determined photometrically using the DPD-1 method (free chlorine) are directly comparable to the values determined by the sensor.

5.1 Cleaning the Electrode / Replacing Membrane Cap and Electrolyte

We recommend disconnecting the sensor from the transmitter for maintenance.

If calibration is not possible due to a low reading, clean the measuring electrode with the supplied grinding paper as follows:

1. Using a blunt object, lift the hose ring out of the guide groove and slide it aside to expose the valve opening.

Diagram: Shows parts 1 (Valve opening) and 2 (Hose ring).

NOTE: Underpressure in the membrane cap can destroy the membrane disc. Ensure the valve opening is not accidentally closed with fingers when unscrewing the membrane cap.

2. Unscrew the membrane cap from the sensor shaft and discard the electrolyte solution.
3. Rinse the electrode finger and membrane cap with clean water and gently dry with a clean paper towel.
4. Clean the measuring electrode with the grinding paper. Place the grinding paper on a paper towel, hold it by a corner. Hold the electrode finger vertically downwards and move its tip over the grinding paper two or three times.

NOTE: The brown deposit on the outer surface (reference electrode) of the electrode finger must not be ground off, as this will destroy the sensor!

5. Fill the membrane cap with fresh electrolyte solution as described in section 3.2, screw it onto the sensor shaft, and make the sensor ready for measurement again.

After replacing the electrolyte solution and/or membrane cap, the sensor must be repolarized (see section 4.1 POLARIZATION). If calibration is still not possible after cleaning the measuring electrode, replace the membrane cap.

5.2 Cleaning

Removing Limescale Deposits from the Membrane Cap: Remove limescale deposits from the membrane cap as follows:

1. Unscrew the membrane cap from the sensor shaft and discard the electrolyte solution (see section 5.1).
2. Soak the membrane cap in 10% acetic acid for several hours.
3. Rinse the membrane cap thoroughly with clean water.
4. Fill the membrane cap with fresh electrolyte solution as described in section 3.2, screw it onto the sensor shaft, and make the sensor ready for measurement again.

5.3 Storage

NOTE: The sensor must only be stored in an unfilled state.

Proceed with storage as follows:

1. Unscrew the membrane cap from the sensor shaft and discard the electrolyte solution (see section 5.1).
2. Rinse the membrane cap and electrode finger thoroughly with clean water and dry them dust-free.
3. Loosely screw the dry membrane cap onto the sensor shaft. The membrane disc must not touch the electrode finger.

5.4 Maintenance Materials and Spare Parts

6.1 Measuring Characteristics

6.2 Application Characteristics

6.3 General Data

Dimensions:

• FCML 412 N: 200 mm length, 25 mm diameter at membrane.
• FCML 412 M12: 175 mm length, 37 mm diameter at connector, 25 mm diameter at membrane.

Membrane cap: M48

Membrane type: Microporous, hydrophilic membrane

Electrolyte: ELY-FCML 412 N (from ZBK-FCML 412 N)

Material:

6.4 Electrical Data

• FCML 412 N:
  • 2-wire connection via permanently mounted cable AK-CL 298
  • Power supply: 12 ... 30 V DC from transmitter
  • Output signal: 4 ... 20 mA
• FCML 412 M12:
  • 5-pin M12 flange connector: for ADA CL/IDS adapter via screw/plug connection
  • Power supply: +/- 5 ... 15 V DC from MIQ/IDS module
  • Sensitivity: -1000 mV/ppm