University of York NO x instrument installation on the NERC Dornier 228 aircraft.

Transcription

1 University of York NO x instrument installation on the NERC Dornier 228 aircraft. Report prepared for: NERC Airborne Research and Survey Facility Firfax Building, Meteor Business Park Cheltenham Road East Gloucester, GL2 9QL UK Report prepared by: Air Quality design, Inc W I-70 Frontage Road North, #105 Wheat Ridge, Colorado USA May 2013

2 Contents DESCRIPTION OF THE EQUIPMENT INSTALLED ELECTRICAL LOAD ANALYSIS HAZARD ASSESSMENT OF THE INSTALLED EQUIPMENT STRESS REPORT FOR THE INSTALLED EQUIPMENT FLAMMABILITY REPORT/ANALYSIS ENVIRONMENTAL TESTING SUMMARY INSTRUCTIONS FOR CONTINUED CHECKS, MAINTENANCE AND PERIODIC SERVICE ii

3 Description of the equipment installed. Instrument functional description The University of York NO x instrument, manufactured by Air Quality Design, Inc (AQD - Wheat Ridge, CO, USA), is a two-channel chemilumescence-based nitric oxide (NO) detector. NO is measured by the chemiluminescence resulting from the reaction of trace amounts of NO in the sample air with percent levels of ozone to form NO 2 (nitrogen dioxide) in an excited state. The NO 2 relaxes by emitting a red photon which is counted using a dry-ice cooled photomultiplier tube. The instrument includes an inlet-based photolytic converter that converts NO 2 to NO, allowing simultaneous measurement of NO and NO 2 (taken together as NO x ). The component parts of the instrument are described below and are shown graphically in Figure 1. NO detector The NO detector contains the dry-ice cooled photomultiplier tube housing, reaction chambers, detector electronics and vacuum valves. The instrument chassis is designed for 19 inch rack-mountability and is manufactured from inch 5052 aluminum with flanges attached to a inch 6061-T6 aluminum front panel and 0.09 inch rear panel. The NO detector is a 5U (8.75 inch) high box, 24 inches deep, and weighs 59 pounds. Ozonizer The Ozonizer contains two corona-discharge ozone generators and associated flow and pressure control elements. The ozonizer uses pure oxygen as a reagent gas and produces about 3% ozone in a flow of 100 sccm (standard cubic centimeters per minute) per channel. The instrument chassis is designed for 19 inch rackmountability and is manufactured from inch 5052 aluminum with flanges attached to a inch 6061-T6 aluminum front panel and 0.09 inch rear panel. The ozonizer is a 2U (3.5 inch) high box, 18 inches deep, and weighs 16 pounds. Inlet system The Inlet system contains a UV-LED based photolytic converter used to convert ambient NO 2 to NO for subsequent measurements, the system flow and pressure control elements, a data acquisition device, and system calibration components. The instrument chassis is designed for 19 inch rack-mountability and is manufactured from inch 5052 aluminum with flanges attached to a inch 6061-T6 aluminum front panel and 0.09 inch rear panel. The Inlet system is a 3U (5.25 inch) high box, 18 inches deep, and weighs 30 pounds. Computer tray The computer tray contains a laptop computer used to control the instrument and a serial communications device. The tray is designed for 19 inch rack-mountability and is manufactured from inch cold-rolled steel with welded corners. The computer tray is a 1U (1.75 inch) high tray, 17 inches deep, and weighs 12.5 pounds. AC power distribution box The NERC-built AC power distribution box contains inverters to converter the aircraft 28 VDC power to 230 VAC power for instrument use. The instrument chassis is designed for 19 inch rack-mountability and is manufactured from inch 5052 aluminum with flanges attached to a inch 6061-T6 aluminum front 1

4 panel and 0.09 inch rear panel. The AC power distribution box is a 3U (3.5 inch) high box, 20 inches deep, and weighs 32 pounds. Pump Pallet The Pump Pallet is a 24 x 30 x ¼ inch 6061-T6 aluminum plate to which is mounted the instrument vacuum pumps and gas cylinders. The pump pallet is designed to be mounted directly to the aircraft seat-rails and weighs 94 pounds. 2

5 Figure 1. Sketch of the University of York NO x instrument installation configuration on the NERC Dornier 228. The various installed components are identified in the table below. ID Description 1 Computer tray: sliding tray containing the system laptop computer and serial communication device 2 Inlet System: Contains a photolytic NO 2 converter, calibration components, and flow and pressure control devices. 3 NO detector: contains a two channel NO detector with dry ice cooled detectors 4 Ozonizer: two channel corona discharge ozone generator (reagent gas for the NO detector). 5 NERC-built AC power distribution box 6 NERC-provided instrument rack 7 Oxygen cylinder forward stop. 8 Calibration cylinder forward stop. 9 Edwards 20i scroll vacuum pump. 10 N/A 11 NO in N2 calibration gas 12 Oxygen cylinder 13 Rear gas cylinder stop 14 Thomas diaphragm pump. 15 Instrument slide (2 per each rack-mounted box except for the AC power distribution box). 16 Pump mounting plate. 3

6 Electrical load analysis. Electrical loads The electrical load requirements for NO x instrument are summarized in Table 1. Values are based on the manufacturer specified power consumption values for the component electrical parts in each instrument chassis. The figures assume 80% efficient AC-DC power supplies (consistent with manufacturer specifications for a convection cooled system (worst case) Table 1. NO x instrument AC power consumption inventory. Component 4 Power consumption, Watts Power requirement, Amps at 240 VAC NO detector with dry ice cooler NO detector with optional/removable thermal electric cooler (TEC) Ozonizer Inlet system Edwards vacuum pump Thomas vacuum pump Totals* *- totals assume use of the optional TEC PMT cooler. The normal mode of operations is with the dry ice cooler. Wire, cable, and connectors All of the wire and connectors used in the instrument are of the type and size specified in the NERC document Engineers Guidelines for the Design and Preparation of Airborne Scientific Instruments. Table 2 lists the wire and cable types used in the instrument. Table 2. Wire and cable used in the NO x instrument Wire/cable application Wire cable description MS number External AC power distribution Teflon-insulated 3 conductor, 16 M27500/16SP3S23 gauge, shielded and Teflonjacketed Internal AC power distribution Teflon-insulated, 16 gauge M22759/32-16 Internal DC power distribution and Teflon-insulated, 22 gauge M22759/32-22 signals External signal and data Teflon-insulated 4 conductor, 24 M22759/24SRS23 communication gauge, shielded and Teflonjacketed Detector signals RG178 coaxial cable, Teflon insulation, braided shield, Teflon jacket n/a Several different connector types are used for AC power and signal distribution these are listed in Table 3. Table 3. Connectors used for external cabling in the NO x instrument. Connector purpose Connector description Connector part number

7 AC power from the AC distribution box AC power connection to the individual instrument chassis Circular plastic connector manufactured by Bulgin, 3 conductor, 12A contact rating, IP68 Threaded bayonet metal shell connector manufactured by AMP, 13 A contact rating Inter-chassis signal transmission MS crimp contact DB connectors (9 and 25 pin). Manufactured by Cannon, 3 A contact rating. BNC 50 ohm solder-type BNC manufactured by Pasternak PX0731/P PX0730/S MS3106A16-7P MS3106A16-7S M24308 series Meets MS3106A16-7S Circuit breakers and line filters Each of the instruments chassis is circuit protected using a thermal circuit breaker rated at 5 A. Inside each instrument chassis the AC power is filtered to minimize interference from noise either into or out of the particular instrument chassis. A block diagram of the external cabling interconnections is shown in Figure 2. Finally, all external cable and the pneumatic PFA Teflon tubing are sleeved in flame-resistant/self extinguishing sleeving. 5

8 Figure 2. Block diagram of external cabling connections for the NO x instrument. 6

9 Hazard assessment of the installed equipment. The NO x instrument presents two hazards that the operator must be aware of. First the instrument uses pure oxygen as a reagent gas for the ozonizer. While the cylinder regulator has pressure relief valves and the oxygen within the instrument is electronically pressure controlled and mechanically flow controlled, care should be taken to ensure that the oxygen connection to the instrument from the cylinder remain free of oil and other debris. Secondly, the instrument produces a low flow of 3% ozone, which, if it escaped the confines of the instrument would be an irritant gas. The instrument installation includes two measures to mitigate this hazard. First, there is a ozone destruction trap on the exhaust side of the pump. Second, the effluent from the ozone destruction trap is vented outside the cabin. If the ozone destruction trap failed, and if the ozone was vented into the cabin the pungent odor of ozone would be readily recognized by the scientific observer and the instrument could be shut down. Finally, every effort has been made to isolate the instrument operator from AC line voltages, but normal caution should be observed. Stress report for the installed equipment. The NO x instrument is installed in a NERC-provided, type-certified instrument rack and on a separate pump pallet, so the two cases will be considered separately. Instrument Rack: For the instrument rack the AQD instrument chassis are secured to the rack in two ways. First, the instruments are bolted through the ⅛ 6061-T6 front panel in four places to the steel DIN rails of the rack using 6mm screws. The front panel attachment acts to resist both forward and rearward movement of the instruments. Second, the instruments are secured to cold-rolled steel telescoping slides to both the front and rear Din rails on each side. The telescoping slides act to resist both sideways and up/down movement of the instruments. The fasteners used to attach the instruments to these points are all at least 55 ksi tensile strength. Considering the heaviest of the instruments as an example, the NO detector at 59 pounds, the loads and safety factors for attachment are shown in Table 4. Table 4. Strength of fasteners attaching the NO detector to the instrument rack. Attachment point Screw size screw area (in^2) Number of screws Holding Strength Box weight (pounds) Safety factor at 9 G Front panel 6mm Slide to instrument Size Slide to DIN rails Size The other instruments are identically attached, but weigh much less, so the safety factors noted for the NO detector are much greater for them. The computer attachment is considered further in the section Additional Considerations. 7

10 Given that the instruments are securely attached to the rack we can consider the overall load of the rack in light of the aforementioned NERC guideline document. The instrument was designed in the software program SolidWorks, so we used that software, in conjunction with measured and assigned weights, to evaluate the load on the instrument rack. Figure 3 shows the rack model, mass, and center of gravity for the loaded rack. The result of this calculation is that the center of mass for the populated rack is at 19.9 inches with a total mass, including the rack itself, of 208 pounds. The intersection of this mass and center of Figure 3. Mass and center of gravity analysis of the loaded NO x rack. 8

11 gravity fit within the Acceptable Rack Load envelope specified in the NERC engineering guidance document. Pump Pallet: The components that are mounted to the pump pallet, including two vacuum pumps and two gas cylinders, are each secured to the ¼ thick plate with four grade-8 ¼ bolts. The material of the bolts has a tensile strength of 120 Ksi. Following the example above, we considered the heaviest of the components, the Edwards vacuum pump at 59 pounds to estimate the stress. Since these components are bolted directly to the plate we must first consider the center of gravity. Figure 4. Mass and center of gravity analysis of the loaded pump pallet. Again, similar to the Solidworks calculation for the rack, we used measured and assigned weights to arrive at the result seen in Figure 4. We calculate a total mass of 115 pounds with a center of gravity of 4.3 inches. We estimate the mechanical advantage of the center of gravity to be about 10, given the center of gravity and the approximate bottom side of the grade 8 bolts where they attach to the various components (nominally 0.5 inch). In either a forward or sideways load we conservatively assign the stress to only two of the four bolts. Given these conditions the stress applied by the Edwards vacuum pump at 9 g would be 5300 pounds, versus the 7600 pound tensile holding strength of two bolts, resulting in a safety factor of 1.4. Additional Considerations. The two additional considerations are the attachment of the computer to the computer tray and the attachment of the gas cylinders to the gas bottle mounts. In both cases we referred to the online calculator website to identify and use appropriate estimates of the strength of materials using the attachment methods employed. For the computer attachment with used a calculation based on plate theory with one unclamped edge to approximate the 0.02 thick type 304 stainless steel z-clamps used to secure the computer to the computer tray. There are three similar clamps employed, two on the front edge of the 5 pound computer and one on the rear edge of the computer. We assumed a 9 g forward load on the computer which translates physically to an upward load on the three clamps. Following the data and figures provide at : 9

12 Diagram of the calculated stress, Maximum stress along the free edge of the clamp, We find that the maximum stress is 154 MPa, well below the 203 MPa yield strength of the stainless material and a safety factor of 1.3. For the gas cylinders, which are secured with two ¾ wide, 0.03 thick type 304 stainless steel band clamps we assumed a fully clamped plate with the stress applied to the upper ½ of the clamp. At 9 g, and a cylinder weight of 40 pounds we calculate a stress on one of the band clamps of 32 psi (360 pounds distributed over 11 in 2 ). Following the calculator for a fully clamped plate we find a maximum stress on 0.02 MPa, a very small number compared to the 205 MPa yield and 515 Mpa tensile strength of the material. Flammability report/analysis. Oxygen is classified as flammable because it is a combustion accelerant. However, the oxygen used in this system is contained with the confines of the instrument. Environmental testing summary. Since this is a bespoke instrument we have not submitted it en suite for environmental testing. Mechanically speaking we have followed established guidelines for materials, fasteners, and fastener attachment methods. Electrically, the system uses commercial, CE-marked power supplies and other electronic components so we assume that radiated emissions are within established guidelines. Instructions for continued checks, maintenance and periodic service. While the NO x instrument may require period cleaning and internal component maintenance for optimal performance, the routine checks from and operational point of view are limited to regular examination of the system attach points, detailed above. We expect that the shortest term replaceable components are the ozone destruction traps (estimated lifetime is 1000 hours of operation), and the Edwards vacuum pump (5000 hours of operation). Calibration of the instrument on an every-flight basis will alert the operator to the need for my detailed cleaning and maintenance. 10

13 System block diagram 11