(1) When taking resistance readings on switch or relay contacts, the common multimeter often produces high, almost meaningless resistance readings due to ...Missing:
Practical Low Resistance Measurements Bob Nuckolls Sr. Engineer/SME Raytheon Aircraft Company Wichita, Kansas Modern digital multimeters limitations:
have two important
through the resistor of interest. A voltmeter is used to measure drop across the resistor INSIDE the current connections. Ohms law is used to calculate the resistance value. This technique eliminates effects of test equipment lead and probe resistance. A practical implementation of the 4-wire measurement technique illustrated in Figure 2. can be assembled in an hour or so with a bill of materials under $10. The outer housing is a plastic project box from Radio Shack. Dual
(1) When taking resistance readings on switch or relay contacts, the common multimeter often produces high, almost meaningless resistance readings due to very low test currents generated within the instrument: A sampling of resistance measurement currents for five different digital instruments showed no current exceeding 1.5 milliamperes. Most measurements were are made at currents on the order of 250 microamperes. (2) Typical off-the-shelf multimeters offer a low resistance measurement on the order of 200 ohms full scale with a resolution of 0.1 ohms. For qualitative measurements of components like switches and relay contacts the technician needs to resolve resistance values of 1 ohm or less with resolution in the milliohms. Contact resistance due to film or corrosion build-up requires a substantial current flow to penetrate contact film. A “4-wire” measurement technique for low resistance is illustrated in Figure 1. A current of known value is caused to run
banana plugs to fit most multimeters along with components to implement a constant current source are readily available from suppliers of commercial components such as Radio Shack, Digikey, Hosfelt, Jameco and others Construction Notes A constant current generator is fabricated from a popular adjustable voltage regulator combined with a 12-ohm resistor. The LM317 (Figure 4) is readily available in the TO220 plastic package from most parts suppliers. The LM317 series, 3-terminal regulators come in a variety of packages and environmental ratings. Any version is suited to this application. Power to bias the test comes from three AA sized alkaline Figure 3. Interior View Component Location cells in series. Spring loaded battery holders have a potential for poor connection to the cells with age and environmental effects. Soldered Calibration connections are easy to make and very reliable The finished fixture can be tested for calibration by Brighten an area on the plugging it into the multimeter while it is set up to measure battery to be soldered current. The fixture fabricated for this article produces a with a file, knife edge constant current of 104 mA. This is expected; the LM317 or edge of grinding voltage regulator is a 1.25 volt device. A 12.0 ohm resistor wheel. The Dremel would be expected to produce a current slightly higher than Moto-Tool with a cut100 mA. For most purposes, this variability is insignificant. off wheel attached works really nice. Use a hot iron to get on and Using the Fixture off quickly each time the cell is touched. The adapter illustrated herein generates 100 milliamperes First, tin the area where of test current. When used in conjunction with a multimeter a wire will attach to the having readout in tenths of a millivolt, the resolution of a cell. Tin the wire and low resistance measurement will be 1 milliohm. then tack it into place on the cell. This device will yield useful resistance measurements up to better than 10 ohms (1.000 volts displayed on multimeter) With a little practice, If your multimeter has a 200 or 300 millivolt range, a 100 the two times you touch milliampere test adapter will display 2 or 3 ohms full scale. Figure 4. LM317 Connections. the cell with the soldering iron should be The low resistance measurement adapter is useful in less than two or three seconds total. Eliminating the battery diagnosing system malfunctions that could be attributed to holder allows construction to be contained in a smaller increased contact resistance in switches or relays. Switches enclosure and eliminates future problems that arise from outside the pressure vessel on turbojet aircraft are poor contact with cells. particularly good candidates for environmental effects,
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especially those under the nacelles or on landing gear struts. When investigating the condition of a switch or relay, it’s useful to exercise the part and observe variations in contact resistance from one measurement to the next. Unless you are offered baseline resistance values as part of a published test procedure, you’ll have to make comparative measurements between a suspected bad and a known good component. Storage Current flows from these cells only while a measurement is being made. Shelf life of an alkaline cell is 5 years or more. Cells in this fixture should not require frequent replacement. To take advantage of the very long shelf life of alkaline cells, be sure to store the adapter in a way that protects the lead wires and/or exposed banana plugs from becoming shorted together.
gross weight and density altitude has ... the elevator to control AOA and power ..... 9 or 14V none unless heated. 12 to 28V. 4 Wan max. 14 or 28V. 0.3 amp.
convey a lot of meaning about the wire and its function - valuable information when ..... (2) Power control or steering diodes are used between the main bus and ...... storage at a float voltage just above the battery's own open circuit terminal ....
operational vehicles made analysis and correction of problems a breeze by comparison; US ..... In a pinch, build your own fixture by soldering two alligator clips ...
To check the receiver IF for correct operation, inject a 10.7 Mhz carrier amplitude modulated ... E. Q520 failure can cause no-stow condition in the antenna mode. ... Refer to page 4-18, section 4.4.3 of the maintenance manual for ...... check A.C. r
the surfaces and eliminates the bonding needed for good sensitivity. ... The Audio Leveling Circuit of the COM units require an IC ...... Unit inop in the middle of the band: Warped wafer switches caused by the mounting lock Covered by Senlce ...
field more readily than some of the more complicated situations which arise. ... M e n bench testing the unit for a no reply light for instance, check the AOC voltage for around 4 ..... Corn receiver sens: 2 uv (hard) for 6db (s+nyn with 1 khz @30% m
Sep 10, 2004 - simple ideas in physics and matters of historical fact. ...... amperes/square-inch of current density and voltage ...... one I use in the lab that has a laptop port and a book full of features. ... with these â the jaws are not harde
Aug 1, 1999 - Angle of attack is the angle be- ... to make carrier approaches using angle .... For information, use SPORT AVIATION'S Reader Service Card.
Aug 1, 1999 - AOA 1. 0°. 8°. Figure A. Looping Maneuver point very clear, a looping ... to make carrier approaches using angle .... etary Software Systems, Inc. and ... award-winning design by ... New 45-page INFORMATION MANUAL: '15.
Oct 2, 2005 - communicating until they have proven its operation in their own aircraft under the ... without impediment through the fiberglass body. Some ... This article will discuss the design of an antenna that is ... were probably looking at a "c
Receiving ground radar interrogations at 1030 MHz, it transmits a coded .... engineering substantiation data whenever such installations incorporate alteration (penetration) of the cabin ..... GTX 320 Airborne ATC Transponder Equipment.
Except as expressly provided herein, no part of this manual may be reproduced, copied, ..... GTX 320/320A Installation Manual. Page 1. 190-00133-01. Rev L. 1. .... with appropriate coupling to the aircraft antenna system is used, operate the test ...
color liquid crystal AOA display, sounds aural warning ... additional circuitry for temperature ... pressure. There is a unique variation of this coefficient of pressure (CP) with angle of .... The coefficient of lift vs. angle of attack relationship
carrier pilots are trained to make car- ... AOA is dangerously high. A green split bar is .... in Figure 2 illustrates the effect that flaps create on the rela- tionship ...
Except as expressly provided herein, no part of this manual may be reproduced, copied, transmitted, disseminated, downloaded or stored in any storage ...
mount the vane assembly and routing the connecting cable through ... (small hole holds Hall sensor). Board with ... span position (bottom green display element ...
quarter wave elements to the inner and outer conductors of the coaxial cable and go with it. Also if you ... single pole double throw type. A switch like .... conductive composite aircraft with some minimum type of mounting bracket. Also there is.
tuations result in ¯ uctuations of the surface potential, which in turn modulate the ... active oxide trap in the vicinity of the quasi-Fermi level over the entire channel ...
First of all I believe that only dipole type antennas should be used in composite ... a transmission was received from an aircraft at a distance of about 170 miles. ... So if you have a 5 watt transmitter into an antenna like this, you get just .5 wa
ring carrier for the Hall sensor and pivot bearing that slides on ... position voltage output from the Hall sensor versus angle ... Note: In ground calibration you will.
All LEDs on x y. 1936 lm. 0.272. 0.189. Red x y. 481 lm. 0.687. 0.306. Green x y. 624 lm. 0.120. 0.635. Blue x y. 119 lm. 0.156. 0.025. White x y. 841 lm. 0.308.