I believe that up until the 80's standard resistors were supposed to be used with mercury wetted contacts. After all, they sold mercury cups/posts for that purpose.
Iih!
I was only afraid of cadmium solder until now...
When you hunt for the next digit in metrology, physics don't care human biology
Cd in solder, Hg on contacts , my amatures are Be ...
When you hunt for the next digit in metrology, physics don't care human biology
Cd in solder, Hg on contacts , my amatures are Be ...
Pure Be oder BeCu?
If you don't inhale Be dust it is quite safe, isn't it?
I calibrate accelerometers and the amarture of the shaker is ceramic or mostly pure berillium. No problem unless you lick it for cleaning
Even our workshop got used to it, because after some years you need to replolish the armature, and you don't what to inhale the dust. (Primary calibration with laser doppler interferrometers) And these workshop guys are awesome.
They also polish the Si-'orange' for the new representation of the kilogram. Different story...
From Wikipedia:
https://en.wikipedia.org/wiki/OhmThe "international" ohm was defined as a mercury column 106.3 cm long of mass 14.4521 grams and 0 °C at the International Electrical Conference 1893 in Chicago.
Well... I'm back at it
This time the magical RS925D!
This was purchased, for pretty cheap, in an attempt to get an ESI 242D system up and going. I opened her up to reapply a new foam seal as well as make sure there are no obvious issues that needed to be addressed. After some quick preliminary tests, it looked like some of the lower decades had slight a hysteresis. The issue seemed to have disappeared after letting the decade, and the K2002 I was using, thermally stabilize together for over 24 hours.
Let's open her up!
100 kOhm decade
10 kOhm decade
1 kOhm decade
100 Ohm decade
Top and Insides of trim pot assembly PCBs and WW resistors for the 100 kOhm, 10 kOhm, 1 kOhm, and 100 Ohm decades
10 Ohm decade
1 Ohm Decade
100 mOhm decade
10 mOhm decade. These units have a fixed minimum resistance of 10 mOhms. Because of this implementation there is no 'zero ohm', similar to insertion loss, measurements need to be taken into consideration. This allows for the displayed resistance value to actually be the absolute value.
100 µOhm Decade fine trim pot
More Goodies!
100 kOhm and 10 kOhm decades
10 Ohm and 1 Ohm decades
1k and 10 kOhm decades
Thanks for sharing. It looks like it in great shape.
Thanks for sharing. It looks like it in great shape.
You're are very welcome! This is my first RS925D I've seen, so I wasn't 100% positive on the condition. It seems as if there is a decent amount of flux residue still on some of the connections... is that normal?
Auch, purple wire resistor on 10K decade looks damaged to me. I have some Fluke PWWs, and those edges are real easy to get damaged and open wires, due to very fine gauge.
Thanks for sharing.
here are pictures from my RS925A for comparison to the RS925D above
This time the magical RS925D!
That is a late one, seems to be from the mid 1980s.
Switches are the weak point, inferior compared with the General Radio counterparts. ESI solved the problem by paralleling several switch wafers. Which actually works fine, until dirty or totally worn out.
It would be a good idea to clean all the switches with a rough paper simulating the movement of the switch blade. You are ready when there is no dirt in the paper. Not easy to access and takes a lot of time, but worth the effort. Absolutely no switch cleaner chemicals!
Another thing worth checking are the screw connections of the slide wire. That is the 4-wire node so the possible change can only be seen in a 2-wire measurement. Open the screws, clean the surfaces and bend the spring washer teeth if required.
The trimmers are better that you would expect, but still the obvious reason for any high decade instability. That specific type is still available but very expensive. Turn back and forth a few times as a preventive measure.
Why not use a switch cleaner (like Caig stuff)?
For electrometers and the like one has to ensure that any cleaner does not touch any isolators such as Teflon, but if done extremely sparingly (e.g. Just on the wiping metal surface) then it does do away with oxidation and the like.
Does it affect calibration if it does not touch insulation?
(By sparingly I mean with a syringe or a wipe, and watch oilers do work well to dispense tiny drops into leaf contacts. )
Auch, purple wire resistor on 10K decade looks damaged to me. I have some Fluke PWWs, and those edges are real easy to get damaged and open wires, due to very fine gauge.
Thanks for sharing.
I didn't really notice that at first, Good Eye! Is the only coarse of action to repair said damage, to replace the resistor?
This time the magical RS925D!
That is a late one, seems to be from the mid 1980s.
Switches are the weak point, inferior compared with the General Radio counterparts. ESI solved the problem by paralleling several switch wafers. Which actually works fine, until dirty or totally worn out.
It would be a good idea to clean all the switches with a rough paper simulating the movement of the switch blade. You are ready when there is no dirt in the paper. Not easy to access and takes a lot of time, but worth the effort. Absolutely no switch cleaner chemicals!
Another thing worth checking are the screw connections of the slide wire. That is the 4-wire node so the possible change can only be seen in a 2-wire measurement. Open the screws, clean the surfaces and bend the spring washer teeth if required.
The trimmers are better that you would expect, but still the obvious reason for any high decade instability. That specific type is still available but very expensive. Turn back and forth a few times as a preventive measure.
Thank you for the advice!
I'll work on this here in the future. Will probably post some before/after pictures, when I get to opening her back up.
I love 925D ,it is a great resistance stanard
That discoloration on the 10K may be an indication of overload or a chemical spill, the coating on these resistors are not very resistant, even isopropyl will soften it up and if you get any on it, it will have to dry out thoroughly but has no lasting effects. You'll have to check the resistor with a high accuracy measurement to see if it is out of tolerance. You can use a contact cleaner like deoxit but do not spray it on the resistors, use a lint-less wipe. Yes there is always some rosin residue left on the solder joints, it is of no consequence. Usually these units require very little maintenance.
I have both a RS925D (part of my 242D) and a RS925A (part of a 242B) which I am going through and giving it a once over. The connections on the rheostat are very important and should be snug (do not over tighten), the resistance element/wiper can be gently redressed with crocus cloth and cleaned. I have found some units with some kind of gooey grease on the rheostat, that attracts dirt, I prefer to keep them clean and dry. These units are more or less sealed in their case, there should be little to no contamination getting in there.
These resistors are wound on a mica card and therefor is somewhat easily damaged, not only the fine wire but the mica so be very careful around them.
Is there a Helmut Singer Sticker?
I remember seeing one on ebay for $1500 obo, it sat on there for years. I think it was a dealer based on the West Coast.
The black monolith is alive. Now the race is on to see which one of us can figure it out first. Mine keeps looking at me wondering when I will stop fixing stuff and start measuring my SR1010 and SR104 resistors.
I think there will be some projects to do soon involving resistance bridges.
She's Alive!!!!
How do you calibrate this black monolith? I have a 242C still sleeping on the floor.
According to the manual you need a 10k reference resistor with 1ppm calibration accuracy (SR-104) and a trimmable 10k/step transfer standard like the hard to find SR 1010 MTx.
The black monolith is alive. Now the race is on to see which one of us can figure it out first. Mine keeps looking at me wondering when I will stop fixing stuff and start measuring my SR1010 and SR104 resistors.
I think there will be some projects to do soon involving resistance bridges.
You're on!
I don't have any of the connectors or adapters so I ended up making my own. We'll see how they turn out, as I have not put everything to the test yet. I spent most of the day cleaning everything up on the outside, getting her looking good, as well as calibrating the 801. The 801 performed very well and needed no adjustments coming from Helmut Singer.
According to the manual you need a 10k reference resistor with 1ppm calibration accuracy (SR-104) and a trimmable 10k/step transfer standard like the hard to find SR 1010 MTx.
Done and done!
Ok. Let's communicate offline and get some details worked out.
We can start a new thread and post any results if you want to do some detailed comparisons of portable standards.
Ok. Let's communicate offline and get some details worked out.
We can start a new thread and post any results if you want to do some detailed comparisons of portable standards.
Sounds good! And yes, I would like that very much.