Using Grant W38 Stirred Bath for Resistance Calibrations

[Hawaii596]

Looking for folks with very high accuracy resistance background.  Starting to work on preliminary stages of getting standards lab set up.  I inherited a Grant W38 stirred bath, for which I am researching details now.  It is a 38 Litre bath rated at +/-0.004 C stability. I think I understand a lot of them use oil (Dow Corning 200???).  This one apparently is rated for use with water.  I'm contacting the OEM for some more info.  As apparently you also need an outboard chiller (which I have to find out if I have or not - probably not) if you want to set temp below ambient.  I'm looking for general thoughts about that detail.  Should I even use a water bath (unless I learn it is compatible for oil use).  I'd use distilled water for maximum dielectric strength, but I feel a little bothered that that is a risk factor.  Maybe just a large container that can sit in the middle of the bath that is electrically isolated from the liquid.  If anyone has used this specific model or any of the Grant Wxx series, I'd like to hear your thoughts.

[scottbp]

Water?  Practically all resistor baths use white (water clear) mineral oil. We order all our silicone fluids for our temperature baths from Clearco, they also sell white food grade mineral oil. www (dot) clearcoproducts (dot) com. (Not affiliated or a paid spokesman, blah blah blah and all that jazz...)

[Hawaii596]

Good input.  After lengthy digging around, I found a vendor that is familiar with Grant W38, and the person told me I could get away with using Dow Corning 200 oil.  I'll also check out the vendor you mentioned.

Do you put your resistors in some sort of plastic or other material container to isolate them from the bath? 

[scottbp]

Since it is not conductive, most NBS type resistors (the cylindrical kind with the terminals on top) you can get away with submerging them directly in oil, though it is a bit messy. We also have a set of SR-1010s that we put in metal loaf pans, then filled the loaf pans up with mineral oil just below the top, so the terminals don't get any oil on them. They're not in a stirred bath, it's just a lag bath to help out with the stability. We store our Thomas 1 ohm resistor in a coffee can full of oil, submerged below the terminals (and careful not to touch the sides). We have been wanting a big stirred bath, but can't seem to find any used, and new ones are cost prohibitive for our budget (and we don't have any place to put it anyway.)

[Hawaii596]

I don't know what they cost new or used, but I inherited the Grant W38 bath.  If you do a google search on Grant W38 it should come up.  I'm not yet sure it works.  And to do within +5 C of ambient on down, it needs an outboard chiller as well (which I don't know if it has or not yet).  Just trying to get everything set up.  I'll have to tinker quite a lot more before I figure it all out.