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Old 13th Oct 2010, 8:28 pm   #1
Roger-M0TDM
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Default LCR Bridges and other Variants

Hi after reading another thread,a fellow member of the forum has aquired a LCR Bridge,without wanting to sound thick.
Can someone please explain,as to what purpose do they serve.What are they used for?
Are they just like a antique version of a DMM in that you can check resistance,capatiance.inductance and other flavours, I'm really interested and curious.
Please put me out of my misery and enlighten me lol.
Best regards.
Roger.
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Old 13th Oct 2010, 9:18 pm   #2
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Default Re: LCR Bridges and other Variants

Hi Roger, basically that is it; an old fashioned version of your fancy all purpose DVM.
HOWEVER! they will show much more as they usually have a loss balance or similar control that gives you an idea of the equivalent series or parallel "loss" resistance of the component.
Once you get used to them they are much more accurate than DVM's.
Have a read up on bridges, they all use the same basic circuit but there are a huge number of varirties.
Failing that see me at Lowton and I'll give you a teach in on them.

Best regards, Ed
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Old 13th Oct 2010, 9:41 pm   #3
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Default Re: LCR Bridges and other Variants

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Hi Roger, basically that is it; an old fashioned version of your fancy all purpose DVM.

Failing that see me at Lowton and I'll give you a teach in on them.

Best regards, Ed
Ok Ed Thanks very much for the kind offer,much appreciated.
When and where exactly is the Lowton meeting?
regards Roger.
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Old 14th Oct 2010, 9:18 pm   #4
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Default Re: LCR Bridges and other Variants

Hi Roger, its on Sun 21 Nov near Lowton on the east lancs road. See meetings section for more details.
If you are lucky you may even find one there!

Ed
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Old 14th Oct 2010, 10:18 pm   #5
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Default Re: LCR Bridges and other Variants

Hi Ed,thanks for the reply,according to the listing its members only,if that is the case.Unfortunately I am prevented from attending.
Best regards Roger...
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Old 14th Oct 2010, 11:12 pm   #6
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Default Re: LCR Bridges and other Variants

You could always join, old chap...!

The important things to realise about LCR bridges are, unlike a DMM, (a) LCR bridges don't measure voltage or current, and (b) they must be used to measure components out-of-circuit, as they apply AC waveforms to the component under test, and readings would be altered by the presence of other components.

The 'loss balance' function is a very effective way of estimating a capacitor's leakage, by the way. I always use my LCR bridge to check capacitors prior to using them in a repair.
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Last edited by Phil G4SPZ; 14th Oct 2010 at 11:19 pm. Reason: Info added
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Old 15th Oct 2010, 9:21 am   #7
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Default Re: LCR Bridges and other Variants

Ed et al
Just so you know the 21st November event has a new venue from the Lowton one. I shall be posting a new thread in a week or so

cheers Mark

PS I shall have the teach in also please!
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Old 15th Oct 2010, 1:14 pm   #8
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Default Re: LCR Bridges and other Variants

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Originally Posted by Phil G4SPZ View Post
The 'loss balance' function is a very effective way of estimating a capacitor's leakage, by the way. I always use my LCR bridge to check capacitors prior to using them in a repair.
Yes indeed. When I'm restoring a radio, it's always interesting to put any Hunts or TCC waxies across the bridge so I can see just how bad they really are. It's also good for testing NOS types as well. Another use is for 'matching' components. I once had to change a couple of 100pF capacitors in an I.F transformer. The originals were 2% tollerance and I had 5% types. I was able to match two capacitors to within 1% using my Marconi bridge.


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Old 15th Oct 2010, 2:11 pm   #9
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Default Re: LCR Bridges and other Variants

Quote:
they must be used to measure components out-of-circuit, as they apply AC waveforms to the component under test, and readings would be altered by the presence of other components.
There speaks someone who hasn't encountered the transformer bridge like the Marconi TF2701 "in-situ" bridge.

It cleverly balances out everything more complex than a simple component that's in parallel with the one you are measuring - and copes better with the remaining parallel combination.

Seriously clever!
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Old 15th Oct 2010, 2:51 pm   #10
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Default Re: LCR Bridges and other Variants

here we have a nice little discussion on capacitance bridges.

http://theradioboard.com/rb/viewtopi...citance+bridge

http://theradioboard.com/rb/viewtopi...bridge&start=0
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Old 15th Oct 2010, 4:21 pm   #11
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Default Re: LCR Bridges and other Variants

Following up on GMB's remarks about transformer bridges. They will indeed normally test insitu components. The usual one is the Wayne Kerr B221, which also appears as MoD CT530. A lovely instrument. Covers a much wider range of circuit values than any other I know of.
I had one once, but found it difficult to use to just check a component when servicing. Not using it every day, I had to look up the manual every time. And measuring results expressed as Conductance needed thought as it is much less familiar.
It was large, so I eventually sold it, and now use a TF2700, which is small. It only takes a moment usually to free one end of the component, which should go to the DET+ve terminal.
Incidentally I have the test leads for the B221 somewhere, with the small connectors which plug into the panel, if any one would like them for the cost of postage. Also the LowOhm adaptor.
Bill.
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Old 15th Oct 2010, 5:06 pm   #12
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Default Re: LCR Bridges and other Variants

Bill, if that's the Q221 I'd be very interested.

PM coming soon

Jim
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Old 15th Oct 2010, 5:52 pm   #13
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Default Re: LCR Bridges and other Variants

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and now use a TF2700,
There must be loads of these about. I know of another which is locked in a cupboard where I used to work. I doubt it will ever be used again and only hope that one of the other engineers will grab it before it's skipped.



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Old 15th Oct 2010, 7:22 pm   #14
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Default Re: LCR Bridges and other Variants

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There speaks someone who hasn't encountered the transformer bridge like the Marconi TF2701 "in-situ" bridge... Seriously clever!
The beauty of this Forum is that you learn something new every day

I have heard of in-situ testers, but "seriously clever" usually means "seriously expensive and unlikely to be affordable by me!" and I confess to never having come across such an instrument. However, the OP asked a general point about an LCR bridge versus a DMM, which I think has been effectively answered now. Says he, trying hard not to sound like a Moderator...
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Old 15th Oct 2010, 8:31 pm   #15
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Default Re: LCR Bridges and other Variants

Like Bill, I now use a TF2700, a Cropico Resistance Bridge, or a wee jappo RS lcr meter. That makes my WK B221 + all it's add-ons redundant. Wish I lived back near Mark along the East Lancs Road - would've off-loaded to someone keen(with structurally heavy shelving), buck-sheesh.

Regards, David
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Old 15th Oct 2010, 9:55 pm   #16
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Default Re: LCR Bridges and other Variants

David
I have shelving!
cheers mark
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