OD OD DIGITAL DISSOLVED OXYGEN CONTROLLERS

Transcription

1 UNI EN ISO 9001:2000 CERT. N BCEL OPERATOR S MANUAL OD OD DIGITAL DISSOLVED OXYGEN CONTROLLERS Rev. A Valid from S/N Input: Scales: Power supply: from polarographic cells 0/19.99 PPM 0/199.9 % O 2 0/199.9 % air saturation 0/199.9 mmhg 110/220 Vac B&C Electronics Srl Via per Villanova Carnate (Mi) Italy P.IVA Tel Fax bc@bc-electronics.it -

2 Index 1 GENERAL PRINCIPLES FUNCTIONAL DESCRIPTION PHYSICAL DESCRIPTION SPECIFICATIONS PHYSICAL INSTALLATION ELECTRICAL INSTALLATION Connecting the power Connecting the cell (probe) Connecting the microtransmitter Connecting alarms, pumps, valves Connecting a recorder Connecting the RTD Checking OPERATING THE SYSTEM Pre-operation check NORMAL OPERATION CALIBRATING THE CONTROLLER Electric zero Zero cell calibration Slope calibration Polarization voltage of sensor PREVENTIVE MAINTENANCE Controller Sensor TROUBLESHOOTING GUIDE

3 1 GENERAL This manual applies to the OD and OD digital controllers. It explains the purpose of the equipment, describes the components of the chain and the procedures for installing the equipment, operating it and calibrating it. Some suggestions are also given for its maintenance. 2 PRINCIPLES In a polarographic cell, if a constant tension is applied to the electrodes, the reduction of the oxygen ions on the cathode generates a current proportional to the oxygen's partial pressure. The intensity of the current produced at a constant temperature and at a given oxygen pressure depends on the quantity and composition of the electrolyte, the cathode's area and the sample's state. Response time depends on the electrolyte's and diaphragm s characteristics. The value of the applied voltage to the anode is chosen in a way that only oxygen can react. In absence of oxygen, the current produced is not exactly zero. In fact, impurities and other factors generate a "dark current" which can be offset by the amplifier. The electrode consumes the oxygen diffused through the permeable membrane (PTFE) and the electrolyte's film, therefore a concentration gradient is established between cathode and sample; the electrodes with a big cathode, with a high output current, consume a lot of oxygen and are more sensitive to the sample's flow and therefore request a large flow and an adequate stirring of the sample. The temperature dependence of the output current is compensated by the automatic temperature compensation of the meter

4 3 FUNCTIONAL DESCRIPTION This system provides a digital readout of the dissolved oxygen of aqueous solutions. In order to satisfy the many requests of such measurements, two types of amplifiers with different ranges have been designed: The model OD for industrial applications and the model OD for fermentation. The mod. OD features: - selectable ranges in PPM, % air, % O 2, mmhg. - auto/manual temperature compensation - temperature and temperature coefficient readout - adjustable temperature coefficient - polycarbonate membrane panel The mod. OD features: - 0/200.0 % AIR saturation scale - automatic temperature compensation A basic dissolved oxygen monitoring system consists of two elements: a monitor unit, and a probe or O 2 cell. The system can be expanded by adding accessories for field applications, recorders, secondary regulators, proportional regulators, special probes and temperature probes to suit particular applications. The controller contains electronic circuits to control the operation of the entire system. It provides a digital readout of dissolved oxygen on a 3 1/2 digit display. There is included an internal circuitry for controlling two alarms, valves, pumps etc. Set-points are independent and programmed by a front-panel control to trigger at any level within the range of the meter. Red LEDs on the panel indicate if the measured value is below the set point A level, or if it is above the set point B level. Red LEDs also indicate the switching of corresponding relays. The controller provides an output of 0/20 ma - 4/20 ma selectable by rear switch (on request 0/10 V or others). The output is proportional to the meter reading, for driving a recorder, remote readout or regulators having an isolated input (not grounded). Zero and slope are adjusted by trimmers 2 and 3 on the front panel

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7 The following features are available: - the set point value is visualized by pushing the button 6 on the front panel - the switching function of relay is inverted by rear switches marked min/max - the regulators have a delay action 0 to 5 seconds by rear trimmers marked DEL A and DEL B - the B regulator, as an " option ", can be supplied as a " window alarm " working over the set point A with the delay action included. - automatic temperature compensation is carried out by means of a 3 wire RTD Pt the input of meters is both by electrodes (probes) or by amplified probes (by microtransmitter). This special probe is completely waterproof and contains the measuring O 2 cell and a microtransmitter which allows a normal electrical cable to be used to receive the signal. With this technical solution, it is possible to make considerably long connections between the measuring point and the controller without signal delay or interference. As a result, fewer additives are consumed and a greater precision of regulation is obtained. Furthermore, the coupling of the instrument and the probe by means of a 4 wire cable, is protected against connection errors. (a 7 wire cable is needed when Pt 100 thermo compensator is installed) Therefore, the installation of the measuring and regulating link can be carried out by non-specialized staff. In the model OD the digital temperature readout is obtained by pushing a button 10 on front panel, as measuring and controlling functions of the instrument are not altered. The digital temperature factor readout is obtained by pushing a button 12. The value of the temperature factor is adjusted by the trimmer 11. The scale is chosen by the selector

8 4 PHYSICAL DESCRIPTION The controller enclosure is designed for surface or panel mounting. It consists of an anodized aluminium front panel and an epoxy-coated metallic case, to ensure the maximum anticorrosion characteristics. (The model OD565.2 has a polycarbonate membrane on the front panel). However a mounting in a splash proof board is suggested for field applications. The figures 3 and 4 show the physical details, dimensions and drill plan of this case. Connections to power supply, loads, recorder, RTD, electrodes/probe are carried out by means of a detachable terminal block on the rear side. Fig

9 5 SPECIFICATIONS Voltage: Input: Output : Scales OD545.2: Scales OD565.2: 110/220 Vac +/-10 % 50/60 Hz from polarographic O 2 cell from microtransmitter /20 4/20 ma dc selectable, nonisolated, 300 Ω max. 0/199.9 % AIR saturation 0/19.99 PPM 0/199.9 AIR saturation 0/199.9 % O 2 0/199.9 mmhg Zero: adjustment +/- 15% Slope: fine adjustment +/- 20% coarse adjustment Temperature: 0/50 C Cell current in air: µa Temp. comp.: automatic 0/50 C Temp. coeff.: 0 to 6 %/K (OD 565.2) 2.3 %/K at 20 C (others on request) (OD 545.2) Temp. sensor: RTD Pt100 Temp. readout: 0/100 C (OD 565.2) Regulators: Switching time: Regulators delay: Relay contacts: +/- 0.25% hysteresis (others as requested) < 0.5 s 0 to 5 s 5 A 220 V resistive load Fuse : 80 ma T (110 V) 32 ma T (220 V) Power: Weight: Size: Option Option Option Option VA max kg 241 x 89 x 157 mm galvanic cell input isolated output 24 Vac power supply window B regulator - 9 -

10 6 PHYSICAL INSTALLATION The controller may be installed close to the points being monitored, or it may be located some distance away in a control area. For a distance between sensor (cell/probe) and controller greater than 30 feet the microtransmitter probe is suggested to avoid signal delay and interferences. The enclosure is designed for panel-mounting. It should be mounted on a rigid surface, in a position protected from the possibility of damage or excessive moisture or corrosive fumes. Immersion probes have a PVC ring to adjust the depth of the cell into the liquid to be tested. Probes may be fastened by hangers with 36 mm. hole. The cable from the probe must be protected by a sheath and not installed near to power cables. Interruption on cables must be avoided or carried out by high insulation terminals. When installing the cell it is suggested to follow the specific instructions given by the sensor s manufacturer. Fig

11 7 ELECTRICAL INSTALLATION The electrical installation consists of: - connecting the power supply to the meter - connecting the cell or the probe to the meter - connecting alarms, pumps, valves if necessary - connecting the monitor output to the recorder or similar devices if required - connecting other optional accessories (RTD P.I.D. regulators) All connections within the controller are made on terminal strips (detachable) located on the rear side. All power and output-recorder connections are made at the 16 pin terminal strip, while input signal connections are made at the 8 pin terminal strip. 7.1 CONNECTING THE POWER - connect ground to terminal 1 - connect ac power to 2 and 3 terminals if power is 110 V - connect ac power to 2 and 4 terminals if power is 220 V - use 32 ma T fuse for 220 V - use 80 ma T fuse for 110 V (connect 24 Vac power to 2 and 4 terminals if option is installed) WARNINGS: - power the device by means of an isolation transformer - avoid mains voltage from an auto-transformer - avoid mains voltage from a branch point with heavy inductive loads - separate power supply wires from signal ones - control the mains voltage value - it is necessary that all ground terminals of each component of the system should be connected together to a sure ground

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13 7.2 CONNECTING THE CELL (PROBE) Electrode cabling is a critical part of the whole system. - use a low noise coax cable on overall length between sensor and input terminals of the meter - avoid interruption on the cable if a coax connector and a high insulation terminal strip are not available - keep the cable away from power wires on the overall length - use microtransmitter in field applications for distance longer than 30 feet between the electrode and the controller. - connect the cathode (Pt) to the terminal 30 marked Pt - connect the anode (Ag) to the terminal 31 marked POL - connect the shield to the terminal 28 marked 0 Electrodes supplied by B&C Electronics have wires marked for the right connection to the meter. 7.3 CONNECTING THE MICROTRANSMITTER The controller may operate with signal by microtransmitter mod Follow the specific instructions for connections. 7.4 CONNECTING ALARMS, PUMPS, VALVES The output connections are made at terminal strip and they consist of two independent relay contacts corresponding to regulator ""A" and regulator "B". Regulator ''A'' terminal 8 marked C : common contact terminal 9 marked NO : normal open contact terminal 10 marked NC : normal closed contact Regulator ''B'' terminal 5 marked C : common contact terminal 6 marked NO : normal open contact terminal 7 marked NC : normal closed contact To provide an ac-line voltage at the relay commons, install jumpers from the ac power terminal 2 to the concerned relay commons marked C. Connect one side of an external line-operated device to the terminal NO/NC according to the requirements of the device, and connect the other side of the device to the line terminal 3 (110 V) or 4 (220 V). The device may be powered by an external independent line following the above procedure. An independent line is suggested if the device consists in a high inductive load. Remember that relay switching inverted by installing jumpers from terminal 12 to 13 (reg. B) and from 13 to 14 (reg. A). Also, the action of relay "B" may be delayed 0 to 5 sec by the trimmer marked DEL B. (rear side)

14 7.5 CONNECTING A RECORDER A current output for a remote recorder or P.I.D. regulators is available on terminals Connect the recorder "high" to terminal "14" and connect the recorder low to terminal "13". Series connection, following the signal's polarity, is required for driving more loads having a total input resistance lower than 300 Ω. Output drives ground-isolated loads only. Most recorders fulfil this requirement but it is recommended to control it. 7.6 CONNECTING THE RTD The meters have the automatic temperature compensation carried out by means of RTD Pt100. The temperature sensor, if not included in the electrode, has to be installed in the same solution being measured, close to the electrode/probe. The jumpers from 22 to 23 and 24 to 25 terminals keep in action the internal temperature compensation adjusted at 20 C. To operate the automatic temperature compensation, remove the two jumpers and connect the RTD as shown in Fig. 5. A three wire connection is suggested to achieve an accurate compensation over a long distance between the electrode and the controller. - connect the end of RTD to terminal 23 - connect the common end of the RTD to terminal 24 - connect the common end of the RTD to terminal 25 - The 3-wire cable must not be interrupted on the overall length. If an extension is needed, the cable must be fastened to the high insulation terminal strip. - Keep the cable away from power wires. The RTD connection as above described allows the OD controller to provide the temperature readout and the temperature's factor readout. The temperature value of a solution is shown by pushing the button 10 marked TEMP. C on the front panel. The temperature readout does not interrupt the measuring and regulating function of the controller. The temperature coefficient is shown by pushing the button 12 and it is adjusted by trimmer 13. In manual temperature operation the temperature value is adjusted by trimmer 11. In the model OD the temperature coefficient is adjusted at standard value 2.3 %/K at 20 C. (others on request) 7.7 CHECKING Before connecting the system to the power supply: - check that all cables are properly fastened to prevent strain on the connections - check that all terminal-strip connections are mechanically and electrically sound - check that the fuse value is right

15 8 OPERATING THE SYSTEM 8.1 PRE-OPERATION CHECK The system's controls and indicators are all located on the front panel. The meter has a digital display 1 that, together with the green LED 4, indicate that unit is on. Push the button 6 and rotate the set-point control 8. The display will show the set point values. The regulators have a set-point check by red LEDs 7 which are part of the circuitry that powers the relay. When the monitored value is below the set-point value, the LED of reg. A is alight and the corresponding relay is pulled in. When the monitored value is above the set-point value, the LED of reg. B is alight and the corresponding relay is pulled in. The cards of the controllers are adjusted at the factory. If sensors and probes have been connected correctly, as described in the above sections, the system should function correctly needing only the zero calibration to compensate the dark current of the cell and the slope calibration. 9 NORMAL OPERATION To operate the system, simply switch on the controller by means of the lever 5 (power switch), and observe the measured dissolved oxygen of the solution on the meter. Adjust the set-point control A and the set-point control B to the setting required for each particular application

16 10 CALIBRATING THE CONTROLLER 10.1 ELECTRIC ZERO This operation may be done, in local or remote applications, only when the electrode or microtransmitter are not connected to the amplifier. - remove the cell connections from terminals (local operation) - remove the connector from microtransmitter (remote operation) - adjust the trimmer 2 marked "zero" in order to read the value 0.00 on the display - repeat the calibration when the measuring has changed. The display will indicate the value (OD 565.2) 10.2 ZERO CELL CALIBRATION This operation may be effected after the electric zero calibration above described and when the cell is connected to the amplifier, in order to read zero on the indicator. This instrumental zero annuls the residual current of the cell zero point, when the cell works in absence of oxygen. Immerse the cell in a freshly-prepared 2 % sodium metabisulphyte solution or in an equivalent media with a total absence of oxygen and operate as follow: 1) local operation - after balance is reached, adjust the trimmer 2 marked "zero" so as to read zero on the display - repeat the calibration when the range is changed (OD 565.1) 2) remote operation - microtransmitter mod is connected - after balance is reached, adjust the trimmer marked "zero" on the microtransmitter in order to reach zero on the display The repeat of the calibration is not needed when the range is changed (OD 565.2) 10.3 SLOPE CALIBRATION Zero point adjustment must precede slope calibration. Electrode's manufacturers supply, with the sensor, the operating instructions for each application. In particular are described the slope calibration procedures under partial pressure, in % of atmospheric oxygen, in PPM. Calibration is usually effected at oxygen saturation under operating pressure since it is the simplest. In calibrating the reading is adjusted to 100 % saturation. In determining oxygen concentration in PPM, the O 2 content of the calibrating solution must be accurately known. The values applying to pure water, adjusted to the prevailing pressure, are described on oxygen saturation tables

17 1) local operation The controller is supplied with "coarse" and "fine" adjustment of sensitivity. The coarse adjustment must be effected when installing the cell, while the fine adjustment is effected during the normal operation. The coarse adjustment is carried out by the rear sensitivity switch marked LO/HI and by rear trimmer marked "sens R73", which compensates for the different sensitivity of cells. When adjusting the coarse sensitivity, check that the "fine" trimmer 3 marked "sens" on the front panel is set in the middle position. 2) remote operation The procedure is similar as per the local operation. The "coarse" adjustment of sensitivity is carried out by trimmer marked "sens" on the microtransmitter, which compensates for the different sensitivity of cells. During the normal operation the "fine" adjustment is effected by the trimmer 3 marked "sens" on the front panel POLARIZATION VOLTAGE OF SENSOR The controller and the microtransmitter are designed to keep a constant polarization voltage at the electrode for its correct operating. This value is calibrated at 675 mv and can be adjusted, if necessary, from 0 to mv by rear trimmer marked "pol R87" in local operation, and by trimmer marked "pol" on the microtransmitter in remote operation. Use electronic voltmeter to check the polarization voltage on terminals of the controller (local operation), on terminals marked "S" and "Pt" of the microtransmitter (remote operation)

18 11 PREVENTIVE MAINTENANCE 11.1 CONTROLLER Quality components are used to give the controller a high reliability. The frequency of such maintenance depends on the nature of each particular application. As in any electronic equipment, the mechanical components, such as switches, relays, potentiometers and connectors, are the most subject to damage. - check for damage of the electrolytic capacitors if the meter is exposed to temperatures above 80 C. - check for damage in all the electronic components if the meter is subjected to excessive voltage - check for damage of the electronic and mechanical components if the meter is dropped - repeat periodically the pre-operation check - check that all the connections are free from moisture and contamination Disconnect the power supply to the monitor before performing the following procedures: Use moisture free air and blow out the interior of the case and terminal board connections as necessary Inspect the printed circuit boards for dirt and corrosion; clean as necessary and blow dry Tighten all the terminal-board connections and mounting hardware Replace the front panel circuit board or the base circuit board 11.2 SENSOR The state of the cell's membrane is critical for the normal operation of the system and should be inspected more frequently when using oil and grease containing water, and in bio- applications. Suggested methods for cleaning the electrode include chemical cleaning and detergent washing (see the chemical auto cleaning system B&C Electronics). See general instructions given by the cell manufacturer

19 12 TROUBLESHOOTING GUIDE Symptoms Probable cause Remedy Neither LED lit nor meter reading No meter reading, but LEDs light Meter reading too high/low Meter reading does not change Alarm circuit does not operate, meter reading OK Slope not sufficient Recorder does not operate Line not connected Incorrect power wiring Fuse interrupted I.C. failure Inside connector Electrode fouled Meter uncalibrated Electrode damage Short circuit Relay contacts Circuit failure Electrode damage Temperature compensation Recorder not connected Output circuits damage Check power Check wiring Replace fuse Replace I.C. Replace circuit board Clean electrode Adjust "sens" Electrode replacement Check wiring Replace base Return to factory Electrode replacement Check jumpers or RTD Check wiring Replace base circuit board See the peculiar troubleshooting guide of the cell connected to the unit

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