Dissolved Oxygen Meter

Table of Contents

I Overview………………………………………………………………………1

II Structural Features and Working Principle………………………………1

          2.1 Structural Features ………………………………………………………1

          2.2 Working Principle ………………………………………………………1

III Technical Parameters………………………………………………………1

IV Functional Characteristics…………………………………………………2

V Installation and Electrical Connection……………………………………2

          5.1 Instrument Installation …………………………………………………2

          5.2 Electrode Installation …………………………………………………3

          5.3 Rear Terminal Block Connection ………………………………………4

          5.4 Electrical Connection …………………………………………………5

VI Function Key Description…………………………………………………5

VII Detailed Operation Instructions…………………………………………5

          7.1 Power On ………………………………………………………………5

          7.2 Main Menu ……………………………………………………………6

          7.3 Submenu ………………………………………………………………6

          7.4 Parameter Description ………………………………………………7

          7.5 Calibration ……………………………………………………………7

VIII Calibration and Maintenance Menu……………………………………8

          8.1 Output Current Calibration …………………………………………8

          8.2 Test Relay Calibration ……………………………………………9

          8.3 Password Modification ……………………………………………9

          8.4 Output Signal Calibration …………………………………………9

          8.5 After-Sales Service …………………………………………………9

IX Routine Maintenance……………………………………………………10

X Completeness………………………………………………………………12

I Overview

The Industrial Dissolved Oxygen Meter (hereinafter referred to as the instrument) is a microprocessor-based online water quality monitoring instrument. It is widely used in industrial water, domestic water, sewage treatment, aquaculture, and other fields for continuous monitoring and control of oxygen content in aqueous solutions.

The instrument features an LCD display; intelligent Chinese menu operation; current or voltage output; freely settable measurement range; high and low limit alarm prompts; two sets of relay control switches with adjustable hysteresis range; automatic or manual temperature compensation; and automatic electrode calibration.

II Structural Features and Working Principle

2.1Structural Features:

The complete measurement system mainly consists of the instrument (secondary meter) and the dissolved oxygen electrode (primary meter). The dissolved oxygen electrode contacts the measured solution, and the instrument displays the oxygen content, temperature, and working status of the aqueous solution.

2.2Working Principle:

The oxygen electrode uses platinum (Pt) as the cathode, Ag/AgCl as the anode, with 0.1M potassium chloride (KCl) as the electrolyte, and a silicone rubber permeation membrane as the gas-permeable membrane. During measurement, a polarization voltage of 0.68V is applied between the anode and cathode. Oxygen passes through the permeation membrane and is consumed at the cathode. The amount of oxygen permeating the membrane is proportional to the dissolved oxygen concentration in water, thus the limiting diffusion current between the electrodes is proportional to the dissolved oxygen concentration in water. The instrument detects this current and converts it into oxygen concentration through calculation. Simultaneously, a thermistor detects the solution temperature and compensates the oxygen concentration for temperature.

     The electrode reactions are:

          Cathode (Pt): O₂ + 2H₂O + 4e⁻ = 4OH⁻

          Anode (Ag): 4Ag + 4Cl⁻ = 4AgCl + 4e⁻

III Technical Parameters

(1) Measurement Range: Dissolved Oxygen: 0～25.00 mg/L; Temperature: 0～60℃;

(2) Measurement Error: Dissolved Oxygen: ±0.2 mg/L F•S; Temperature: ±0.5℃

(3) Automatic Temperature Compensation: 0～60℃;

(4) Electrode Residual Signal: <1‰;

(5) Response Time (90% of final value): <60S at 25℃; <30S at 35℃;

(6) Stability: Drift <2% F•S per week under constant pressure and temperature;

(7) Signal Output: 0～10mA (load resistance <1.5KΩ); 4～20mA (load resistance <750Ω);

               0～5VDC or 0～10VDC (requires pre-order);

(8) Two Sets of Relay Control Contacts: 3A 240VAC, 6A 28VDC or 120VAC;

(9) Power Supply: 220VAC±10%, 50±1Hz, power ≤3W;

           24VDC, power ≤1W (requires pre-order);   12VDC, power ≤1W (requires pre-order);

(10) Dimensions: 96×96×130mm;

(11) Installation Method: Panel Mounting (Embedded); Cutout Size: 91×91mm;

(12) Wall-mounted: Waterproof Wall-mounted Box Dimensions: 300(H)*200(W)*167(D)mm;

(13) Instrument Weight: 0.6kg;

(14) Operating Environment:

      Ambient Temperature: -10～60℃;

      Relative Humidity: Not more than 90%;

      No strong magnetic field interference except the Earth's magnetic field.

IV Functional Characteristics

※ Intelligence: Uses a single-chip microcomputer to complete dissolved oxygen measurement, temperature measurement, and compensation;

※ User-Friendly Interface: Menu-driven operation structure, users operate according to on-screen prompts;

※ Multi-Parameter Simultaneous Display: Simultaneously displays dissolved oxygen value, temperature value, and working status;

※ Software-Settable Output Mode: Software selectable 0～10mA or 4～20mA output;

※ Freely settable measurement range and alarm upper/lower limits; Upper/lower limit alarm prompts;

※ Two sets of relay control with adjustable hysteresis range;

※ Self-set Password and Service Guide: Users can set or modify passwords to prevent unauthorized access and misoperation; Provides technical support and after-sales service contact methods.

※ RS485/RS232 communication interface for connection to a computer.

V Installation and Electrical Connection

The instrument should be installed in a clean, dry, well-ventilated, and vibration-free location. There should be some space around the instrument for operation and maintenance. The instrument should be as close as possible to the sampling point for easy electrical connection. The distance between the instrument and the sensor should not be too far to facilitate calibration operations.

5.1 Installation: The instrument is suitable for panel embedding installation. The cutout size is 91×91mm as shown in Figure 1. Embed the instrument into the square hole and fix it with the provided bracket.

Instructions: Pass the cable through the protective conduit, connect the electrode thread to the thread of the protective conduit (use waterproof tape for waterproofing), ensure waterproof connection between the two protective conduits to prevent solution penetration and cable corrosion inside the conduit, fix the protective conduit on the mounting bracket, and cover the top of the protective conduit with a black waterproof rubber cap to prevent rainwater from entering.

③ Flange Mounting: Customized flange mounting based on user requirements.

④ Other Methods: If no suitable installation method is found above, please contact the manufacturer for custom special methods.

5.3 Rear Terminal Block Connection

Wiring Instructions:

1、AHNC Relay High Alarm Normally Closed Contact

2、AHCOM Relay High Alarm Common Contact

3、AHNO Relay High Alarm Normally Open Contact

4、ALNC Relay Low Alarm Normally Closed Contact

5、ALCOM Relay Low Alarm Common Contact

6、ALNO Relay Low Alarm Normally Open Contact

7、220VAC Live Wire/24VDC+/12VDC+ (Please note the instrument power supply)

8、Neutral Wire/24VDC－/12VDC－ (Please note the instrument power supply)

9、Electrode Terminal (Dissolved Oxygen Electrode Cathode －)

10、Electrode Terminal (Dissolved Oxygen Electrode Anode ＋)

11、Electrode Terminal (Temperature Electrode)

12、Electrode Terminal (Temperature Electrode)

13、Electrode Terminal (Shield)

14、Empty

15、Dissolved Oxygen Value Output Signal －

16、Dissolved Oxygen Value Output Signal ＋

17、～24、Empty

25、Communication ＋ (Optional)

26、Communication － (Optional)

5.4Electrical Connection: Connection between the instrument and sensor electrode: Power supply, output signal, relay alarm contacts, and sensor electrode connections are all at the rear of the instrument. Wire according to Figure 3. The fixed cable lead length for the electrode is conventionally 5-10 meters. The terminal end has labeled tabs; insert them into the terminals with the same numbers at the rear of the instrument and tighten.

VI Function Key Description

There are 6 touch keys on the panel: (Left), (Right), (Up), (Down), Exit, and Confirm, as shown on the cover.

(Left): Moves the cursor left during data input, or moves the menu left;

(Right): Moves the cursor right during data input, or moves the menu right;

(Up): Moves the menu up or increases the value;

(Down): Moves the menu down or decreases the value;

Exit: Switches between the measurement screen and menu screen, or goes back to the previous menu, state, or cancels input data in the menu screen;

Confirm: Selects menu items, confirms and ends data input, or confirms certain states.

VII Detailed Operation Instructions

7.1 Power On: Before use, check all pipeline connections and electrical connections. After power is connected, the instrument enters the measurement state within seconds.

The dissolved oxygen value is the main display, temperature and status are the secondary displays.

The status prompt line displays the following information: 1. Normal 2. High Limit Alarm 3. Low Limit Alarm

7.2Main Menu: Press the "Exit" key in the main display state to enter the main menu:

7.3Submenu: Before measurement, the "Parameters" should be set or modified according to the actual situation; otherwise, the existing set values in the instrument will be used. When the cursor is under the "Parameters" menu, press the "Confirm" key, enter the password, and then press "Confirm" to enter the submenu with multiple items. Entering this menu requires the correct password (initial password is 0000). After entering this menu, a flashing cursor will indicate the current parameter item. Move the cursor up or down according to the selected parameter, then press the "Confirm" key to enter that parameter item for setting or modification.

Important Note: When entering a password or modifying numerical parameters, use the Up and Down keys to change numbers "0～9", "minus sign", and "decimal point"; use the Left and Right keys to change position.

Backlight Adjustment Method: When the instrument displays as shown in the right part of Figure 4, press and hold the "Up" key until a grid background appears. Release the "Up" key, then press the "Up" or "Down" key as needed to adjust the instrument's backlight to a suitable level.

7.4Parameter Description:

1) "Display Mode": Options are μg/L (1000μg/L=1mg/L), %, and mbar. Conventionally select μg/L.

2) "Zero Current I0" and "Slope S": These two items are used to set the electrode zero current and electrode slope. The calibrated I0 and S are also recorded in the parameter menu.

3) "Atmospheric Pressure": Used to set the current atmospheric pressure.

4) "Alarm High Limit", "Alarm Low Limit", and "Alarm Hysteresis": These three items are used to set the alarm high and low limits (Alarm High Limit > Alarm Low Limit); and to set the hysteresis value for the control quantity. This function is used to control equipment such as metering pumps and valves.

5) "Output Upper Limit" and "Output Lower Limit": These two items are used to set the dissolved oxygen measurement range corresponding to the current output. Output Upper Limit > Output Lower Limit.

6) "Output Current": This menu item is used to set the instrument's current output mode, either "0-10mA" or "4-20mA". The relationship between the output current and the measured dissolved oxygen value is:

0～10mA output mode: I=｛(D-DL)/(DH-DL)｝×10mA;

4～20mA output mode: I=4mA＋｛(D-DL)/(DH-DL)｝×16mA.

Where: I- Output current value, D- Currently measured dissolved oxygen value, DH- User-set "Output Upper Limit"; DL- User-set "Output Lower Limit".

7) "Temperature Mode" and "Manual Temperature": "Temperature Mode" is divided into "Actual" and "Manual". "Actual" means the temperature is measured by the temperature sensor; "Manual" means the temperature is set manually and is unrelated to the actual solution temperature. This function is mainly used for simulation debugging, reducing the need for a resistance box. (It can also use "Manual" temperature setting if the measurement is not affected by temperature).

8) "Meter Number": Used for numbering when adding a communication interface.

7.5Calibration Instructions:

Since the zero current and slope of each oxygen electrode are different, and as the filling solution is consumed, the zero current and slope will gradually change during use, showing aging. Moreover, each time the filling solution is added or the membrane is replaced, it will cause changes in the zero current and slope. Therefore, regular "calibration" is needed to ensure sufficient measurement accuracy. Entering this menu requires the correct password (initial password is 0000).

"One-Point Air Slope Calibration": Before calibration, the oxygen membrane at the electrode head should be filled with filling solution. After installation, keep the electrode head clean and insert it into the water sample. Then, accurately connect the electrode cable to the instrument according to the labels and power on for activation for 1-2 hours. Remove the electrode from the water sample and place it vertically in the air. Gently absorb the water droplets on the electrode head with clean filter paper. Then operate the instrument to enter "One-Point Air Slope Calibration" as shown in the left figure below. After the input current becomes relatively stable (usually about 5 minutes), it will calibrate automatically, or manually press the confirm key to continue. Then the calibration result reference is displayed as shown in the right figure below. Press the confirm key first, then the exit key. The displayed value after calibration should comply with or be close to Appendix A, see page 11.

After calibration is completed, it can be put into the water sample for measurement. Users only need to perform one-point air slope calibration when putting it into use.

VIII Calibration and Maintenance Menu

8.1Output Current Calibration: This function is mainly used for simulated calibration of the output current, allowing users to check the accuracy of the instrument's output current over the full output range. Secondly, when connected to a recorder or traditional lower computer, it can check whether the recorder and lower computer sample correctly to troubleshoot faults. Entering this submenu will show a warning, reminding you that before using this function, you should ensure that arbitrary changes in the output current will not cause any harm. Press the "Confirm" key to continue, and enter the current output setting screen as shown below. The screen displays the current output current. Use the up/down or left/right keys to change the current output current. Press the "Confirm" key to stop the change, or press the "Confirm" key to pop up a box and directly input the current value that needs to be calibrated. At this time, measure the output current with a multimeter; it should be the same as the displayed value or within the error range.

Special Reminder: When using this function, since the output current is arbitrarily set by the user and may change over the full range, confirm that the regulating controller or computer connected to the output loop will not produce control outputs with adverse consequences.

8.2Test Relay Calibration: Entering this submenu displays as shown above. This function is used to test the quality of the alarm control relay output. Press the Up key for High Alarm: Disconnect or Connect; Press the Down key for Low Alarm: Disconnect or Connect.

When the controlled load rated current is less than the current the relay can承受, connect as shown in the left figure below (power supply must not exceed 220V);

When the controlled load rated current is greater than the current the relay can承受, an AC contactor needs to be added. Connect as shown in the right figure below.

8.3Password Modification: After entering this submenu, first enter the "Original Password" (initial password is 0000), then enter the "New Password" and press "Confirm" to complete the user password modification.

8.4Input Signal Calibration: This function is used by the manufacturer for simulation debugging.

8.5After-Sales Service: This menu displays the contact information of the seller.

IX Routine Maintenance

The instrument generally does not require routine maintenance. If a fault occurs, please contact our company and carry out adjustments and repairs under the guidance of the company's technical personnel. If users do not have calibration conditions or need维修, please contact the manufacturer.

For the use and maintenance of the sensor (oxygen electrode), please note the following points:

(1) When disassembling and assembling the electrode, do not damage the permeation membrane (oxygen membrane) or break the glass bulb at the tip of the electrode core.

(2) When the value displayed by the instrument differs greatly from the actual measured value, the filling solution inside the oxygen electrode may have dried up and needs to be refilled. Specific steps are as follows: A. Slowly unscrew the black cylindrical permeation membrane (oxygen membrane) at the electrode head. Note: Do not damage the permeation membrane or scratch and break the glass bulb at the top of the electrode core; B. Pour out the remaining filling solution in the cylinder (if the outer surface of the oxygen membrane is contaminated, rinse it clean with清水. Do not let the oxygen membrane touch other things, and do not rinse the inside of the oxygen membrane with water.). Refill with the original filling solution and then install it onto the oxygen electrode core. Excess filling solution will naturally discharge through the electrode's vent groove (ensure no bubbles are left in the cylinder during installation), then carefully screw on the stainless steel outer sleeve. After powering on for activation for more than 1 hour, perform "One-Point Air Slope Calibration" again before putting it into operation.

(4) When the site is out of water for a long time and not in use, remove the electrode, clean it, pour out the filling solution inside the membrane, put on the protective cap, and it is recommended to store the electrode dry.

(5) If the electrode is damaged or失效, it needs to be replaced. If the oxygen membrane is damaged, it needs to be replaced.

Appendix A (Normative Appendix)

Oxygen Saturation Table in Water at Different Temperatures

Note: This table is quoted from JJG291-1999 Appendix C.

Under different atmospheric pressures, the dissolved oxygen content can be calculated as follows.

         A_S=A•

Where: A_S——Solubility at atmospheric pressure P(Pa);

      A——Solubility at 101,325 (Pa) atmospheric pressure;

 P——Pressure, Pa.

X Completeness

Note: Please check the completeness of the purchased instrument before use.

For other series of analytical instruments from our company, please visit our company website for inquiries.

Instrument Usage Tips:

1、How to retrieve a forgotten password?

Answer: Enter the after-sales service menu. When you see the manufacturer's contact information, press the "Left" and "Right" keys simultaneously. At this time, you need to enter the password "54321". After entering, move the cursor to the bottom row "Password" to view the current instrument password.

2、How to correct the temperature error value (This method is only for small errors; if the actual value differs greatly, check whether the instrument and electrode are working properly)?

Answer: Enter the after-sales service menu. When you see the manufacturer's contact information, press the "Left" and "Right" keys simultaneously. At this time, you need to enter the password "54321". After entering, move the cursor to "Temperature Calibration". If the temperature value is偏小 (too small), directly input the error value. If the temperature value is偏大 (too large), first input the minus sign and then input the error value.

3、How to correct the dissolved oxygen error value (This method is only for small errors; if the actual value differs greatly, check whether the instrument and electrode are working properly)?

Answer: Enter the after-sales service menu. When you see the manufacturer's contact information, press the "Left" and "Right" keys simultaneously. At this time, you need to enter the password "54321". After entering, move the cursor to "Calibration". If the dissolved oxygen value is偏小 (too small), directly input the error value. If the dissolved oxygen value is偏大 (too large), first input the minus sign and then input the error value.

Brief Operation Instructions

This manual contains all the operational details of the instrument. The following brief operation instructions are provided to help users quickly learn how to operate the instrument.

1、Instrument Installation: Fix the instrument on the panel of the instrument cabinet or inside the instrument box, prevent direct sunlight or water splashing, connect the power cable, but do not power on yet (the instrument can be powered on for warm-up for 1-2 hours before formal use);

2、Electrode Installation: According to the site requirements, install the electrode in a submerged manner (with submerged protective conduit, please do not directly immerse the electrode cable in the solution), pipeline type (with stainless steel or PVC mounting base), or other installation methods. Refer to page P3 for reference;

3、Remove the organic glass protective cap or rubber protective cap from the electrode head and install the electrode properly;

4、Connect the electrode terminals to the corresponding numbered terminals on the rear of the instrument one by one according to the labels;

5、Connect the power supply to start measurement (One-point air slope calibration is required before use).

Important Safety Information

Please read and comply with the following:

· When the instrument is optionally equipped with a 220VAC power supply, the rear side of the instrument casing carries high voltage, which may lead to hazards. Before approaching this area of the instrument, be sure to disconnect the line power.

· Wiring or repairs should be performed by professionals and only on de-energized instruments.

· Once the instrument exhibits safety issues, immediately power off the instrument to prevent any unintentional operation.

For example, it may be in an unsafe state under the following circumstances:

1) The instrument shows obvious damage;

2) The instrument cannot operate normally or provide specified measurements;

3) The instrument has been stored in an environment with temperatures exceeding 50°C for a long time.