1 Ohm standard resistor Repair - UK Vintage Radio Repair and Restoration Discussion Forum

G4_Pete · 14th Jun 2016, 9:47 pm

I received the attached some while back from someone who thought that brown paper and a skimpy bit of bubble wrap was sufficient to send a vintage Gambrell Croydon 1 Ohm 3 amp lab standard through the post. I negotiated to keep it rather than send it back and have it thrown in the bin.

I wanted a One Ohm standard to fill a gap in standards I keep occasionally calibrated for no good reason other than to measure things and check my vintage kelvin and Wheatstone bridges.

The question is do I fix this, let it settle, and then get it calibrated but I am wondering if the solder joint that is broken is standard solder and if I just solder it on the end of the terminal whether that is good enough for a standard resistor. I am surprised that there was not a more mechanical joint , in the past I have seen the post ends slotted and the wire captive in the slot before soldering.

Any comments on the best way forward.

Pete

trobbins · 17th Jun 2016, 9:22 am

Is the bad joint the actual terminal for the resistance, and are the wires used for kelvin connection of current circuit and voltage sensing circuit?

If so then what would the nominal accuracy specification be of the resistor when originally sold?

What accuracy specification can you achieve nowadays - do you use an uncalibrated current source, and another reference resistor and two reference voltmeters?

G4_Pete · 23rd Jun 2016, 5:25 pm

Hi Trobbins, sorry for the delay been away for a few days and just to give the full background of what I was doing.

Prompted by your comments and looking more closly this is the potential terminal that appears to have sheared off , which is the good news, but unfortunatly the current loop is also joined close to that junction so without great care the current wire could also become unsoldered. However I may drill the potential terminal ,solder in a short length of wire then use this thiner wire to make the joint to minimise the heat.

As for specifications I have not found any for the Broken standard but my nearest calibrated standard is 100 ohms measured at 99.9988302 mean over 300 measurements at 20 Deg C. with the other 10 and 0.1 resistors specified at 0.005 and 0.01 Pct respectivly, but with no current cal certificate. So my aim before the postal disaster was the get the 1 Ohm calibrated by the same test house as the 100 Ohm and then cross check my 0.1 and 10 Ohm standards and then use these on my Cropico KB3. All for no other reason than technical interest.

However as I type this I am thinking I may now just find another 1 Ohm standard as It is perhaps not sensible getting a precision calibration done on a pathched up standard.

Pete

And

14th Jun 2016, 9:47 pm	#1
G4_Pete Hexode Join Date: Feb 2014 Location: Southampton, Hampshire, UK. Posts: 419	1 Ohm standard resistor Repair I received the attached some while back from someone who thought that brown paper and a skimpy bit of bubble wrap was sufficient to send a vintage Gambrell Croydon 1 Ohm 3 amp lab standard through the post. I negotiated to keep it rather than send it back and have it thrown in the bin. I wanted a One Ohm standard to fill a gap in standards I keep occasionally calibrated for no good reason other than to measure things and check my vintage kelvin and Wheatstone bridges. The question is do I fix this, let it settle, and then get it calibrated but I am wondering if the solder joint that is broken is standard solder and if I just solder it on the end of the terminal whether that is good enough for a standard resistor. I am surprised that there was not a more mechanical joint , in the past I have seen the post ends slotted and the wire captive in the slot before soldering. Any comments on the best way forward. Pete Attached Thumbnails

17th Jun 2016, 9:22 am	#2
trobbins Heptode Join Date: Oct 2009 Location: Melbourne Australia Posts: 901	Re: 1 Ohm standard resistor Repair Is the bad joint the actual terminal for the resistance, and are the wires used for kelvin connection of current circuit and voltage sensing circuit? If so then what would the nominal accuracy specification be of the resistor when originally sold? What accuracy specification can you achieve nowadays - do you use an uncalibrated current source, and another reference resistor and two reference voltmeters?

23rd Jun 2016, 5:25 pm	#3
G4_Pete Hexode Join Date: Feb 2014 Location: Southampton, Hampshire, UK. Posts: 419	Re: 1 Ohm standard resistor Repair Hi Trobbins, sorry for the delay been away for a few days and just to give the full background of what I was doing. Prompted by your comments and looking more closly this is the potential terminal that appears to have sheared off , which is the good news, but unfortunatly the current loop is also joined close to that junction so without great care the current wire could also become unsoldered. However I may drill the potential terminal ,solder in a short length of wire then use this thiner wire to make the joint to minimise the heat. As for specifications I have not found any for the Broken standard but my nearest calibrated standard is 100 ohms measured at 99.9988302 mean over 300 measurements at 20 Deg C. with the other 10 and 0.1 resistors specified at 0.005 and 0.01 Pct respectivly, but with no current cal certificate. So my aim before the postal disaster was the get the 1 Ohm calibrated by the same test house as the 100 Ohm and then cross check my 0.1 and 10 Ohm standards and then use these on my Cropico KB3. All for no other reason than technical interest. However as I type this I am thinking I may now just find another 1 Ohm standard as It is perhaps not sensible getting a precision calibration done on a pathched up standard. Pete And