Salt Baths

ventura · 10-07-2008 -- 17:24:49

Who here has some experience with setting up and verifing salt baths?

I am using Lithium Chloride, Magnesium Chloride Hexahydrate, and Sodium Chloride.

I just wanna get folks opinions on them overall.

USMCPMEL · 10-08-2008 -- 08:06:50

I have never really trusted them. You have to keep a close eye on the enviroment and make sure air is ciculating and all that good stuff. I use salts but I verify them with a vaisala to verify the actual humidity.

OlDave · 10-08-2008 -- 08:19:52

OK, overall opinion. I hate them!

I have never been comfortable trying to rate them at 1% despite the claims of ASTM E104. (Get it! Read it!)

E104 mentions that temperature instabiltiy of ±0.1°C can cause instabilities of 0.5%RH. Believe it! Temperature is your worst enemy with salts. I had my salt solutions in a small cooler lined with extra foam when I used them.

About all I can say is be patient, very patient. They take a long to to equilibrate after you disturb them. And even then be very skeptical of any results.

Good luck. You'll need it.

bAdbOb · 10-11-2008 -- 18:18:45

I have used saturated salt solutions for the last 10 years with excellent results. I mix the solutions in 250 or 500 ml dewars flasks per E104. The flasks are covered and nearly submersed in a silcone oil bath at 25 deg C. Temperature is easily regulated to +/-0. 02 deg C.

I only use them to calibrate temperature/humidity recorders and personal pens so the small opening in the dewars flasks are not an issue.

Be sure to use reagent grade salts for best results.

OlDave · 10-12-2008 -- 06:41:50

I never had the luxury of a spare temperature bath, but I can see where that would easily solve the temperature stability issue. I think I'll just stick with my Thunder Scientific 2500 though. I don't miss the old salts a bit.

ventura · 10-14-2008 -- 20:17:02

I have a customer approved procedure in setting up the saltbaths. I do not think that they know or understand the full aspects of this type of calibration. I am working on a solution as I do not in my professional opinion feel that this is an adequate calibration for what I work with and what I work around.

I appreciate the input thus far.

ventura · 10-14-2008 -- 20:28:20

Quote from: OlDave on 10-12-2008 -- 06:41:50
I never had the luxury of a spare temperature bath, but I can see where that would easily solve the temperature stability issue. I think I'll just stick with my Thunder Scientific 2500 though. I don't miss the old salts a bit.

I am actually trying to get that too. I had one in the Air Force and I would love to get one here for my operation. We will just have to see. 700 Billion dollar bail outs for exec's that go on luxery vacations kinda put a kink in the way my world operates. As it does with the majority of us on here.

Hawaii596 · 10-15-2008 -- 16:51:18

If I were bad-mouthing things I didn't trust in RH cals, it would be sling psychrometers. They will out-and-out lie to you. When you study their specs in details, you realize they truly don't have any; and true full technical data on them is non-existent.

ventura · 10-17-2008 -- 22:24:04

Quote from: Hawaii596 on 10-15-2008 -- 16:51:18
If I were bad-mouthing things I didn't trust in RH cals, it would be sling psychrometers. They will out-and-out lie to you. When you study their specs in details, you realize they truly don't have any; and true full technical data on them is non-existent.

Yea I have on of those too, but I don't use it.

Hawaii596 · 10-28-2008 -- 08:12:05

I guess I'm kind of in the middle....

We have a big old Thunder Scientific at my new place of employment (send me a PM and I'll tell you - don't like to post such things).

I really liked my General Eastern at my old work with the D2 chilled mirror. I got really good repeatability after learning some finesse with inserting probes etc. We have approximately the same General Eastern system here (different model chilled mirror), and unfortunately due to cost of operation, they've shut down the old Thunder Scientific and are going to sell or otherwise disposition it.

As for salt baths. The Vaisala HMK11's aren't too bad. If you use some finesse with them you can get (I think) less than 1%RH variation on them. I've actually used some home made salt methodology in the past. We built a plexiglas chamber with two levels and holes drilled through between them. Made sure to have a good rubber seal around the door. We installed an RTD temp probe inside the chamber. Then placed a pyrex cake pan in the bottom, spread the salts over the bottom of the pan. Then used a clean sprayer bottle filled with distilled water, and sprayed a saturated amount of water on the salts. And, of course, we only used good reagent grade certified salts. We closed the door, put the RH chart recorder in, and got pretty good repeatability. We used this method only for chart recorders that didn't have a detachable probe. So bottom line is it was adequate for that application.

I think a lot of the accuracy in salt baths is in technique and good temp monitoring.

I have moderate views about the various methods, with the exception that I'll take the opportunity to once again bad mouth sling psychrometers.

ventura · 10-29-2008 -- 18:12:00

I agree with ya HI,

I am redesigning my Salt Baths and hopefully I can maintain my temperature and Salt solutions in a manner that I can get good precise and accurate measurments.

We will see. I will keep yall posted on my process and my design.

Hopefully when we move to LEAD I will get either the Thunder or Fluke system. Oh that would ease the pain and trouble.