Leeds & Northrup Potentiometer (measuring instrument)

Discussion in 'Marketplace' started by GopherT, Feb 2, 2015.

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  1. GopherT

    Thread Starter AAC Fanatic!

    Nov 23, 2012
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    Not the 'Pot' you may be thinking about. Used for calibrating thermocouples.

    Clean as the day it was built - 1980's?
    Includes manual and "Temperature - EMF Tables for Thermocouples"

    Post or PM if you are interested.

    image.jpg image.jpg image.jpg image.jpg
     
  2. profbuxton

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    Feb 21, 2014
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    Great instrument. Used one for quite a few years when I worked for L&N from 1975. It could measure temperature signal from thermocouple and output thermocouple emf to recorders,indicators etc. I wonder how accurate the standard cell in it would be now. I don't know if they are still available.
     
  3. GopherT

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    I have never used it and haven't taken the time to learn to use it. I would be interested in learning how to check the accuracy of the standard cell. What voltage level should I hope for?
     
  4. profbuxton

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    Feb 21, 2014
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    From the dim recesses of my memory I believe it was a Weston Standard Cell. A glass "H" pattern thingie with some sort of mercury electrodes and some sort of liquid electrolyte. Puts out a fixed voltage at about 1.something volts over a wide temperature range for a long time as it is unloaded. Just used as a voltage reference. I can't recall how to zero the dvice now but I'm sure its in the manual.
     
  5. GopherT

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    The glass bulb is there and the electrolyte is crystal clear. I'll measure the voltage tonight.
     
  6. Reloadron

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    Jan 15, 2015
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    A true classic that brings back so many memories. That one is a fine specimen too. The saturated standard cell voltage should be 1.o18638 and yes, they used the Weston Cell. For using it an accurate mercury in glass standard thermometer was placed across the EMF terminals. Yours even has the book.The early ones actually had a mechanical galvo I think before the meters.
    I had one set aside where I worked with a few other classic items. Came back from a few weeks vacation and they had trashed it because some idiot said it was obsolete junk and they needed space for his project (which never materialized). That SOB was the only guy in a large operation I ever wanted to hurt! :) They filled a dumpster with much of my cool stuff. Thank God I rescued a set of L&N Standard Resistors.

    Ron
     
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  7. GopherT

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    Nov 23, 2012
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    @Reloadron
    @profbuxton

    Thanks for the info on the Weston Cell reference voltage of 1.018638V
    Just measured the Weston Cell with 3 different meters.
    1.0179 V (20,000 count meter)
    1.020 V (6000 count meter)
    1.019 V (2000 count meter)

    None of my meters have been calibrated in some time.

    Maybe I should just keep it as a voltage reference?
     
  8. Reloadron

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    Jan 15, 2015
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    Actually it's more practical for thermocouples. Years ago the saturated cell was the DC Reference standard, today we have standards like the Fluke 732 and 734 systems. The one I worked with and remember well was the Fluke 7105 system. It was a stack in a 19" rack mount panel consisting of:
    Fluke 720A Kelvin Varley Divider
    • Fluke 750A Reference Divider
    • Fluke 335A DC Voltage Standard
    • Fluke 721A Lead Compensator
    • 845AR High Impedance Null Detectors

    That was the system of the day. You could use it as a millivolt reference standard I guess. The divider network in them are excellent. I would have been interested in it but I have shelves of stuff I need to get rid of. :) Matter of fact I should make a list and put it here if anyone is interested.

    Ron
     
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