Low frequency loop impedance, Physics

Low frequency loop impedance:

Low frequency loop impedance testing is a useful method complementary to DC bonding testing.  A visual inspection of cable bundle shields, complemented by a low frequency loop impedance test, gives good confidence in the integrity of the shielding provisions. 

Low frequency loop impedance testing is a method developed to check that adequate bonding exists between over braid (conduit) shields and structure.  To achieve the shielding performance required, it is often necessary that both ends of a cable bundle shield be bonded to aircraft structure.  In such cases, it is hard to check bonding integrity by the standard DC bonding test method.  If the bond between shield and structure at one end is degraded while the other one is still good, there is little chance to find this defect by performing DC bonding measurements.  The remaining bond still ensures a low resistance to ground but the current loop through the shield is interrupted, causing degradation of shielding performance.  The fault can easily be detected by performing a low frequency loop impedance test. 

The test set-up requires simple test equipment, refer to Figure.  A current of about 1 kHz is fed into the conduit under test while measuring the voltage necessary to drive that current.  Other versions of the loop impedance test arrangement use different frequencies (200 Hz is typical), and provide the resistive and reactive parts of the loop impedance. 

1919_LOW FREQUENCY LOOP IMPEDANCE.png

The test equipment consists of a generator operating at 1 kHz feeding an injection probe and a current monitoring probe, connected to an AC millivoltmeter.  A voltmeter connected to the generator enables the voltage necessary to drive the current to be measured.  1 kHz is a high enough frequency to drive the injection and the monitoring probes and is also enough to avoid specific RF effects, like non-uniform current distribution along the loop under test. 

If, in practice, the current is set to 1A, the voltage figure, when expressed in millivolts, gives the loop impedance in milliohms directly.  The loop impedance is normally in the range 1-100 milliohms.  In this range, accurate results can easily be achieved. 

If too high loop impedance is found, the joint determining the problem has to be identified.  This can be performed by measuring the voltage drop across each joint.  The joint with the high voltage drop across it is the defective one, refer to Figure. 

1442_LOW FREQUENCY LOOP IMPEDANCE1.png

As there is no need for a wide band swept RF generator, the test equipment can be quite simple and easy to handle.  Hand held battery powered test equipment, especially designed for production monitoring and routine maintenance, is available on the market.  

 

Posted Date: 9/13/2012 8:17:40 AM | Location : United States







Related Discussions:- Low frequency loop impedance, Assignment Help, Ask Question on Low frequency loop impedance, Get Answer, Expert's Help, Low frequency loop impedance Discussions

Write discussion on Low frequency loop impedance
Your posts are moderated
Related Questions
Passing Lane A passing lane or overtaking lane is the lane on a multi-lane highway or motorway closest to the center of the road or the central reservation.

Textile industry: High speed drives are essential with wide range of control, small & medium motors are employed. Commutator motors and synchronous motors are used.


What are fibers optics made of? For visible light or lighting purposes spectrum transmission, several types of fibers are used. Glass in very suitable strands which have to be

(1) In Boolean algebra only two types of state variables (0 and 1) are permitted. (2) The variables (A, B, C ....) of Boolean algebra are subjected to three operations.

An experiment with two spikes Use the drill for a rotation machine as in the above experiment. Unite two spikes by attaching the point end of every to the end of a 15 cm length

Q. For projectiles fired at identical speeds but a variety of angles from the ground, neglecting air resistance also the curvature of the Earth at what angle will the maximum horiz

Q. Illustrate what is the direction of null vector? Answer:- There are two probable answers to this 1) It contain no direction 2) It points in every direction Ans

what are the structure of the seeds