RE: LFM test rig
If you just need the flow over the unit then get a good length of tube (air conditioning duct, round / square or rect in section) large enough to take your unit with space around it, a variable speed desk fan and a hot wire or mechanical (vaned) anemometer* (air velocity measuring instrument). Place unit in middle of tube, the fan at one end and if a hot wire anemometer then place thru a drilled hole in the duct positioned well down stream of unit, if a vaned type then probably just have to place at end of duct (but a little way in). The duct will need to be fairly long (wrt the UUT) to reduce turbulence effects. Knowing the air velocity, and cross sectional area of the duct you can calculate the volume flow rate. If you stick thermocouples in the duct before and after the UUT you could get a rough calculation of dissipation too, (depending on the flow rates involved). *Anemometers: http://rswww.com 188-1125 Pitot tube,Digitron,AF200,anemometer 188-1119 Anemometer,kit,Digitron,AF200 or hire one or borrow one from your local friendly heating and ventilation/ process extract company. Chris -Original Message- From: Dan Mitchell [mailto:dmitch...@eoscorp.com] Sent: Tuesday, May 04, 1999 12:50 AM To: 'emc-pstc' Subject: LFM test rig My company produces AC to DC Power Supplies. I have been directed to make a quick and dirty test rig that will allow me to put a predetermined airflow in LFM over the unit. Does anyone know of a website that describes something like this or have had experience building such a test rig and would be willing to share their expertise. Daniel W. Mitchell Product Safety Associate Engineer EOS Corp. - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators). - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
RE: LFM test rig
Daniel, The key item which you should have is an anemometer probe. They are available at reasonable prices. This will allow you to measure airflow at the power supply under test. A simple box (length several times width and height to linearize flow) with fans mounted at the outlet end will be all that is needed, plus a variable supply to throttle back the fans until the correct LFM is measured. You will need a couple of holes in the side of the box for probe access. Keep the holes small - most hot wire type probes are less than half an inch in diameter. CFM (fans required) = LFM X Cross-sectional Area of box. Have Fun Scott ORIGINAL MESSAGE My company produces AC to DC Power Supplies. I have been directed to make a quick and dirty test rig that will allow me to put a predetermined airflow in LFM over the unit. Does anyone know of a website that describes something like this or have had experience building such a test rig and would be willing to share their expertise. Daniel W. Mitchell Product Safety Associate Engineer EOS Corp. - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
Re: LFM test rig
Dan, One advantage to giving advice that is outside of the realm of my core competency is that if I make a fool of myself I hopefully won't get flamed too bad (Harmonics anyone?) I am familiar with SCFH (standard cubic feet per hour), SCFM (standard cubic feet per minute), and LPM (liters per minute); if LFM is a similiar unit of volumetric flow rate I think I can help. I am also assuming you want to provide a controllable amount of flow rather than measure the existing flow in your product. If this is the case you should be able to use a flowmeter. This is a vertical column, with a tapered ID (internal diameter) and a small ball inside. when air flows through it the ball rises and the flow rate is read from markings on the outside of the column. Dwyer makes them; and if you are like many engineers of my acqaintance and coudn't resist a free 20 lb. library from Omega (especially when they started throwing in Dilbert cartoons), you can see an example of one in the flow and level volume. Most flowmeters of this type have pipe thread fittings or barb type connectors. They also have a knob on the front for a needle valve to control the flow. If you connect the inlet with tubing to a source of compressed air (regulated) and run the outlet tubing into your unit you will have a controllable air flow. If your product has numerous air slots tape the end of the tubing to one and tape over all other inlets and openings (except the exit) so all the air flows through your unit and out the desired exit. If you do not have inlet slots or you want to bring the flow closer to the internal part of concern you can lift a portion of the case and feed the tubing through using tape to seal the seam. You should have a diffuser at the end of the tube (or aim it at a diffusing structure already present to prevent direct impingement of the high velocity air stream on to the part(s) of concern (trust me, you DO NOT want to hear an EMC engineer try to talk knowledgably about enthalpy, entropy, or those other fun heat transfer and fluid flow terms). If you are more concerned with the air flow around your product than through your product as it seems you might be from your original message, the job is easier (or at least requires less tape). In this case you build a box to put your product in. Attach a fitting to the box for the outlet tubing from the flowmeter and add some exit ports at the opposite end of the box for the air to exhaust. If this helps you I am : Paul McCoy emmas...@execpc.com If this is useless information I am: some worthless hacker, stealing the web identity of a fine engineer to drag his name through the mud Dan Mitchell wrote: My company produces AC to DC Power Supplies. I have been directed to make a quick and dirty test rig that will allow me to put a predetermined airflow in LFM over the unit. Does anyone know of a website that describes something like this or have had experience building such a test rig and would be willing to share their expertise. Daniel W. Mitchell Product Safety Associate Engineer EOS Corp. - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators). - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
RE: LFM test rig
You may consider using a (big) plastic bag, of known volume. Attach it to the opening where the air comes out. Using a stopwatch you can find the time to fill the bag. Now you know air volume per time thru the PSU. Regards, Ari -Original Message- From: EXT Dan Mitchell [mailto:dmitch...@eoscorp.com] Sent: Tuesday, May 04, 1999 2:50 AM To: 'emc-pstc' Subject: LFM test rig My company produces AC to DC Power Supplies. I have been directed to make a quick and dirty test rig that will allow me to put a predetermined airflow in LFM over the unit. Does anyone know of a website that describes something like this or have had experience building such a test rig and would be willing to share their expertise. Daniel W. Mitchell Product Safety Associate Engineer EOS Corp. - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators). - This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to majord...@ieee.org with the single line: unsubscribe emc-pstc (without the quotes). For help, send mail to ed.pr...@cubic.com, jim_bac...@monarch.com, ri...@sdd.hp.com, or roger.volgst...@compaq.com (the list administrators).
