Electronics > Metrology

Leeds & Northrup 4737-A20 tear down

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Hello all,

in the mean time the L & N 4737-A20 Guarded Wheatstone Bridge has arrived.

I did not power it up, but I opened it, to take some photos, see below:


Rear Panel:

Inside view, whole device:

Front terminals:

Front small switches:

Resistors on range selector and 1st stage:

Resistors on stage 5:

Resistors on stage 6:

Housing, heavy aluminum die cast:

Hafe fun to look at details - Guido

Beautiful. Thank you for the pictures!

Thanks for the teardown. Interesting that the lowest decade is 0.01 Ohms. I figured that it would have been 0.1ohms like the 4232. It looks like your unit is newer than mine. Cool to see those smaller super accurate resistors.

Interesting that the lowest decade is a continuous wire.  I presume each segment was adjusted down by filing, with no way to add resistance back in, and then the assembly was enamelled.

The vey lowest resistor part does not have to be that accurate - some +-10% may be acceptable there. No trim needed, just get a reasonable good length of the wire.
The tricky part is more with the switches, to get a stable and low constact resistance.


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