ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  
Pages: [1]   Go Down

Author Topic: How do you test a loop?  (Read 2888 times)

Al Clayton

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 79
How do you test a loop?
« on: March 24, 2009, 11:20:27 AM »

I received a call from a  facility that has a Hearing Assistance Loop system. I have no idea how to tell if it's working or not!
I understand that it is just a big coil of wire that surrounds the hall, driven by a big 'ol power amplifier. It was a retrofit situation, so the coil is in (Plastic) wire mold at the junction of the wall and floor around the perimeter of the facility.

I've got signal at the input, Signal at the output. With my inductive "Wand" I can tell that there is signal coming from the coil.

Any ideas? Is there a standard for these in terms of field strength? How would one measure it? Are there meters available for testing/calibrating these systems?

We install a lot of IR and FM systems, which are easy to test!
Logged
Beer is proof that God Loves us and wants us to be happy. - Ben Franklin

Horray Beer!

Jason Lavoie

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 896
Re: How do you test a loop?
« Reply #1 on: March 24, 2009, 01:23:39 PM »

your wand will pickup the signal even if the wire is broken. be sure to measure the impedance of the loop to make sure that the wire is still a loop

other than that, I've never had to diagnose more than a broken loop or a dead amplifier. I'm also interested in any testing methods or field strength calibration.

Jason
Logged

Al Clayton

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 79
Re: How do you test a loop?
« Reply #2 on: April 03, 2009, 10:39:07 AM »

I went to the site intead of my tech.

Loop impedance at 1kHz is 36 ohms.

Amplifier is an ASHLY FTX-1501 operating in bridged mode.

Good strong signal level, & plenty of headroom throughout the system.

I had the school audiologist there and she tested it with a t-coil hearing aid. Loop is working, but the level is very low.

Oh, and guess what else I found, The wiremold is the metal stuff, Secured to the floor with tapcons. I wonder if that has anything to do with it?  Rolling Eyes

Gotta love it!
Logged
Beer is proof that God Loves us and wants us to be happy. - Ben Franklin

Horray Beer!

Al Clayton

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 79
Re: How do you test a loop?
« Reply #3 on: April 03, 2009, 12:07:05 PM »

Sorry, Double posted.
Logged
Beer is proof that God Loves us and wants us to be happy. - Ben Franklin

Horray Beer!

Jason Lavoie

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 896
Re: How do you test a loop?
« Reply #4 on: April 03, 2009, 04:00:58 PM »

Al Clayton wrote on Fri, 03 April 2009 10:39

I went to the site intead of my tech.

Loop impedance at 1kHz is 36 ohms.

Amplifier is an ASHLY FTX-1501 operating in bridged mode.

Good strong signal level, & plenty of headroom throughout the system.

I had the school audiologist there and she tested it with a t-coil hearing aid. Loop is working, but the level is very low.

Oh, and guess what else I found, The wiremold is the metal stuff, Secured to the floor with tapcons. I wonder if that has anything to do with it?  Rolling Eyes

Gotta love it!


hmm.. obviously that's not right.. has the loop ever worked well? probably not.

if the wiremold isn't grounded at all it might work a bit, but obviously you need to get the wire out of it for the system to be any good.

Jason
Logged

Henry Cohen

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1315
Re: How do you test a loop?
« Reply #5 on: April 03, 2009, 05:06:03 PM »

Once you remove the loop from the magnetic shielding (the metal Wiremold), it would also be preferable to mount the loop up higher off the floor so the magnetic field doesn't couple with the metal parts of tables and chairs as strongly. Even [non-electro] magnetic fields benefit from unobstructed propagation paths.
Logged
Henry Cohen
Production Radio Rentals
----------------------------------
"Every new radio emitter since Marconi’s 2nd transmitter has caused interference to other systems!" - Michael Marcus, Oct '07

Jason Lavoie

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 896
Re: How do you test a loop?
« Reply #6 on: May 21, 2009, 06:57:05 PM »

just came across this today and remembered this old thread.

http://www.nti-audio.com/Home/Solutions/InductionLoops/tabid /249/Default.aspx

using the NTI signal generator and analyzer (plus the mentioned third party sensor) it is possible to calibrate your loop to a standard field strength. (though I have never needed that much precision it's nice to know that it's possible)

Jason
Logged
Pages: [1]   Go Up
 

Site Hosted By Ashdown Technologies, Inc.

Page created in 0.034 seconds with 18 queries.