Best Practice Guide, Servomex 2700

Transcription

1 For full installations details refer to the. Best Practice Guide, Servomex 2700 Mounting: General Guidelines: Servomex 2700 Control Units and air supplies (utilities units) should, ideally, be mounted within easy reach of one another to aid routine calibration. They should also be mounted as close as possible to the Sensor Head to minimise the analyser s response time to calibration gases, to help maintain the stability of the air supply units and to minimise the effects of pressure drops. Follow the guidelines for maximum separation of the Sensor Head and Control Unit described in the Servomex 2700 Installation Manual. Servomex 2700 Sensor Head Mounting: Ambient Temperature: Ensure that the operating ambient temperature is in the range of 20 C to +70 C and that the Sensor Head is protected from radiant heat sources or from direct sunlight (in ambient temperatures over 30 C). This can be achieved by installing a Heat Shield between the Sensor Head and the source; a thin metal sheet is usually adequate. Radiating Heat Source Heat Shield Sensor Head Orientation: The Sensor Head may be mounted in any orientation, except with the terminals box directly above the sensor enclosure or with the mounting flange facing directly upwards. Servomex 2700 Best Practice Guide, B Page 1 of 7

2 For full installations details refer to the. Servomex 2700 Control Unit Mounting: Ambient Temperature: Ensure that the operating ambient temperature is in the range of 10 C to +55 C and that the Control Unit is protected from radiant heat sources or from direct sunlight (in ambient temperatures over 30 C). This can be achieved by installing a Heat Shield between the Control Unit and the source; a thin metal sheet is usually adequate. Servomex 2700 Utilities Panel Mounting: Ambient Temperature: Ensure that the operating ambient temperature is in the range of 10 C to +50 C and that the Utilities Panel is protected from radiant heat sources or from direct sunlight (in ambient temperatures over 30 C). This can be achieved by installing a Heat Shield between the Utilities Panel and the source; a thin metal sheet is usually adequate. All pressure regulators, flow meters and gauges exhibit variations of output with changes in ambient temperature (their temperature coefficient). Although Servomex has chosen products that have good rejection to ambient temperature variations, utility units should be installed in locations with relatively stable ambient conditions. Ideally temperature swings from one extreme to another should be avoided. Instrument air and other gases supplied to the utilities panel must have dew points of at least 5 to 10 C less than the minimum anticipated ambient temperature. Air Supplies and Calibration Gases: General Guidelines: All instrument air supplies used should be clean, dry and free from oil and dirt. For optimum performance, only one analyser should be used in conjunction with an air supply or utilities unit. The minimum air supply pressure to a Servomex utilities panel should be 15psig (1barg) and the air consumption (depending on aspirator, calibration and blow back options), at this pressure should be between 0.75 to 1.5l/min. All pressure regulators, flow meters and gauges exhibit variations of output with changes in ambient temperature (their temperature coefficient). Care should be taken to choose products with either a good rejection to changes in ambient temperature or to install air supply units in stable ambient conditions. Servomex recommends that the Servomex 2700 is initially checked/validated with check gases every week and then calibrated as required. This period can be extended as a result of operating experience. For optimum performance, it is also recommended that the analyser calibration is carried out at both the low and high calibration points. Servomex 2700 Best Practice Guide, B Page 2 of 7

3 For full installations details refer to the. NOTE: Experience has shown that for best calibration results the calibration sequence should be Air, followed be 0.3% O 2 balance N 2, followed by 1000ppm CO balance Air. Recommended Calibration Gases Gas Composition Oxygen Sensor Combustibles Sensor Zero Air HIGH LOW 3000ppm(v) O 2 balance N 2 LOW N/A 1000ppm(v) CO balance Air N/A HIGH Aspirator Air Supply: The aspirator air supply is used to extract the sample from the flue. Under typical flue pressure conditions, air consumption is usually 1.5l/min at 3 to 5psig (0.2 to 0.3barg), to give a sample flow of 300ml/min. The factory tested aspirator pressure is marked within the terminal s box of the Sensor Head. In applications where the process pressure is close to that of ambient pressure (within 0.5psig) set the aspirator pressure to the pressure shown on the label. For other process pressures, please consult Servomex for installation details. Care should be taken to fit regulators and gauges that give suitable resolution over expected pressure ranges. As the inlet pressure to the aspirator is directly proportional to sample flow rate, stable aspirator pressure regulation is of the utmost importance for a stable measurement. Two-stage regulation is recommended. A additional primary regulator maybe required to reduce the supply pressure to more manageable pressure levels. Servomex recommends that the stability of the pressure regulation should be better than 5% of the aspirator set-point i.e psig, for combustibles only and dual sensor versions of the Servomex 2700 and better than 10% for oxygen only versions. Auxiliary Air Supply: The combustibles only and dual sensor versions of the Servomex 2700 require auxiliary air to supplement the level of oxygen present in the combustibles sensor. As the auxiliary air mixes with the sample gas, any fluctuations will affect the measurement of the analyser; therefore the auxiliary air supply should be regulated to give nominally 100ml/min, stable to ±1ml/min. Blow-Back: Blow-back must not be used instead of a suitably specified filtered sample probe. If you have any concerns over the included sample probe, consult Servomex prior to installation. Blow-back pressure must not exceed 15psig (1barg). Servomex 2700 Best Practice Guide, B Page 3 of 7

4 For full installations details refer to the. Calibration Gases: Calibration gas flow rate should be set via a suitable flow meter to ml/min, maximum inlet pressure 15psig (1barg). Auto Calibration: Time must be given to allow for calibration pipe work to be flushed and for the sensors to stabilise. Field experience shows that 4 to 5 minutes are usually adequate, depending on the separation between gas cylinders and the Probe Head. Analyser Purge Options: Sensor Head: Corrosive Purge: This purge is to help prevent corrosion within the Sensor Head and is supplied through the terminal s box and left to freely vent through the breather port. It does not provide protection for use in hazardous areas. A flow rate of between 50 to 100ml/min of instrument air is required, at an inlet pressure of 50 to 100mmH 2 O. Hazardous Area Purge: Refer to local standards. Control Unit: Corrosive Purge: This purge is to help prevent corrosion within the Control Unit. It does not provide protection for use in hazardous areas. A flow rate of between 100 to 200ml/min of instrument air is required, at 50 to 100mmH 2 O. Hazardous Area Purge: Refer to local standards. Air Supplies and Calibration Gases Specification Aspirator Oxygen Only Typically 3 to 5 psig (0.2 to 0.3barg) stable to 10% of set point. CO only and dual Typically 3 to 5 psig (0.2 to 0.3barg) stable to 5% of measurements set point. Auxiliary air (CO only and dual Nominally 100ml/min stable to 1ml/min. measurements) Blow Back No greater than 15psig (1barg) Calibration Gases ml/min Purge Gases Sensor Head 50 to 100ml/min, at 50 to 100mmH 2 O Control Unit 100 to 200ml/min, at 50 to 100mmH 2 O Servomex 2700 Best Practice Guide, B Page 4 of 7

5 For full installations details refer to the. Cabling: The electrical terminations in the Servomex 2700 are suitable for 20AWG (0.5mm 2 ) to 14AWG (2.5mm 2 ) solid and 16AWG (1.5mm 2 ) stranded conductors. Both the Control Unit and Sensor Head have independent AC power supplies. Interconnecting Cable Requirements Analyser Interconnecting Cable Maximum Cable Length Oxygen Only Minimum of three twisted pairs with an overall 300m screen. Maximum loop resistance of heater Combustibles Only Oxygen and Combustibles Note: interconnections is 4. Minimum of six twisted pairs with individual and overall screens. Maximum loop resistance of heater interconnections is 4. Minimum of nine twisted pairs with individual and overall screens. Maximum loop resistance of heater interconnections is m 100m To utilise the optional sensor head temperature facility at the control unit, add one extra twisted pair to the above cable specification. Recommended Cables and Suppliers (Always check manufactures specification for full compatibility before use). Analyser Cable Supplier Part Number Oxygen Only Alpha Belden B A Combustibles Only Alpha 5620B2008 Oxygen and Combustibles Belden.. Alpha Belden A 5620B A The maximum loop resistance limit of 4 is required for the sensor heater lines (two per sensor); the sensor outputs, temperature signals and bridge supply wires need not be limited by this, but they are limited to a cross sectional area of 0.5mm 2 for electrical termination. Depending on installation environment, it may prove cost effective to use interconnecting cables with more twisted pairs, but with a smaller cross sectional area per core and to run the cell heater wires in parallel to produce the maximum 4 loop resistance. Ensure that good EMC practices are observed when making connections. In order to avoid ground loops, it is essential that cable screens associated with the signal cable(s) connecting the Sensor Head, do not terminate directly to ground, they should be terminated to TB5/13, TB3/9 and the stud terminal S, see figure 10 Installation Manual. The Control Unit must be connected to a local EMC earth and with the signal cable(s) Servomex 2700 Best Practice Guide, B Page 5 of 7

6 For full installations details refer to the. screens terminated to the control unit enclosure. The recommended method is to terminate the screen at the cable gland, if this is impractical, the screens maybe terminated to the M4 threaded studs adjacent to the cable entries. Any conduit or screen associated with the power supply, should be grounded at the cable gland or conduit entry to the Sensor Head or Control Unit enclosure in accordance with local wiring regulations. Installation and Commissioning: After installation, the Sensor Head should not be left on the flue without being powered for an extended period, as condensation may form within the sample pipe work. The Sensor Head should be removed from the process and protected against external contamination, or left with 600ml/min of instrument air running through the calibration port, until the analyser can be fully commissioned and placed online. Initial Start-up and Analyser Warm-up: Typical Analyser Warm-up: On powering the 2700 Control Unit and Sensor Head, the Sensor Head and sensors are heated. These temperatures are interlocked with the aspirator solenoid valve, to determine when to start extracting a sample; thus protecting the analyser from condensation forming within the sample pipe work. The Sensor Head and the combustibles sensor heating starts at switch on; with the oxygen sensor waiting until its ambient temperature has been raised to 65 C, before it in turn switches on. Using the Diagnostics menu, see Servomex 2700 Quickstart Manual, section 3.2, you can monitor the warm-up of the Sensor Head and sensors. You should see the Sensor Head and combustibles sensor temperatures rise slowly from switch on, stabilising in 15 to 60 minutes, depending on the ambient temperature. The oxygen sensor will rise slowly at first, until its temperature is over 65 C, then more quickly as it is heated, until it stabilises in 5 to 15 minutes. Servomex 2700 Best Practice Guide, B Page 6 of 7

7 For full installations details refer to the. When the unit is fully up to temperature, the following diagnostics values are typical: Probe Head C Oxygen Sensor.. 0mV (on air); 80mV (on 0.3%O 2 ) Oxygen Sensor C COe Sensor to 60mV (on air); plus either 40 to 110mV (on 1000ppmCO) for ppm range COe sensors or 15 to 40mV (on 1000ppmCO) for ppm range COe sensors COe Sensor C At this point the Sensor Head solenoid valve will activate, and the analyser will start to extract a sample from the process. It is recommended that the analyser is not calibrated at this point, but left for three hours to fully reach thermal equilibrium. If the analyser is now calibrated good results will be achieved but, due to the large thermal mass of the analyser, some measurement drift may be experienced over the next 24 hours. It is recommended that for best results the analyser is calibrated once more after 24 hours. Routine Maintenance, Calibration and Servicing: The Servomex 2700 is designed to be a low maintenance product, with the minimum of support required after commissioning. The Sensor Head contains an internal 5 m sintered stainless steel filter, which prevents contamination of the Sensor Head. On processes with higher dust levels, greater than 0.2g/m 3, Servomex supply a range of standard and special filtered sample probes, that prevent the transmission of dust from the process into the Sensor Head. If you have any concerns over the included sample probe, consult Servomex prior to installation. General Guidelines: The analyser should initially have its calibration, catch pots and air filters checked once per week; this can then be adjusted depending on site experience, but should be at least monthly. Analyser flow rates, air supplies, probes and filters (internal and external), should be checked once per year, as well as the whole analyser and cabling for general signs of wear. In some applications, these times may need to be shorter, depending on experience. Servomex 2700 Best Practice Guide, B Page 7 of 7