Mystery measurement device - Page 1
Forum section: electronics / general

author: Whales
author_rank: Super Contributor
timestamp: July 16, 2015, 04:03:01 am
content: I found this being thrown out in a pile of old computers at my Uni:It obviously has something to do with gas measurement, but I'm not sure what. The graph paper is easily scratched to reveal a black inner material that the scribing arm reveals. The blue plastic box looks like an oven with a large ceramic resistor in the centre.There is no model number information anywhere on the box and I could not find any info using the model number on the internally attached plate. The use of a 220V -> 110V transformer and the few pieces of writing on it heavily suggest this was American made, but beyond that I don't know anything.I particularly like the timer mechanism with a synchronous AC motor and lots of switches. I'm tempted to scavenge the scriber but I don't know what I'd use it (and the limited supply of paper) for other than hosting earthquakes.

author: edpalmer42
author_rank: Super Contributor
timestamp: July 16, 2015, 04:58:35 am
content: I don't know why you can't find any info.The eighth picture shows that it's made by Baseline Industries. Google for that and TCD and the first hit tells you that it's a Thermal Conductivity Detector which is part of a gas chromatograph and what it does. Since I know nothing about and have no interest in gas chromatographs I stopped there.

author: Whales
author_rank: Super Contributor
timestamp: July 16, 2015, 05:28:37 am
content: Thanks edpalmer, I'm reading into it now.

author: PedroDaGr8
author_rank: Super Contributor
timestamp: July 16, 2015, 05:35:50 am
content: Quote from: edpalmer42 on July 16, 2015, 04:58:35 amYep this is a VERY old and antiquated gas chromatography machine. Gas chromatography is a chromatography method in which the mobile phase is a gas with a solid stationary phase. This is in contrast to most other chromatographic systems in which the mobile phase is a liquid. The "column" in these systems is typically a coiled loop of wire, or in this case likely the coiled pipe in picture #9. The thing that looks like an oven, is just that. The material in the gas phase must be kept in the vapor phase at all times, requiring elevated temperatures. Additionally, the amount of interaction with the stationary phase is often dependent on temperature. So the "column" is kept heated at all times, in order for it to work.A TCD is a simple device (basically a filament) placed in the gas flow stream. It has it's temperature stabilized such that the voltage/current are held in steady state. This results in a consistent degree of heat transfer to the surroundings. When an analyte comes through, it changes the heat transfer properties of the gas flow stream. Typically causing a drop in temperature of the filament. This change in temperature changes the resistance of the filament, causing the system to change either the voltage or the current flowing through it to return to steady state. This change is what is plotted on the chart recorder paper.

author: Mashpriborintorg
author_rank: Regular Contributor
timestamp: July 16, 2015, 05:43:05 am
content: It looks like it is packed with nice re-usable partsScientific or medical devices are some of the most interesting things to take apart

author: Whales
author_rank: Super Contributor
timestamp: July 17, 2015, 01:43:21 pm
content: @PedroDaGr8: thanks for the write-up. Have you operated one of these before?Quote from: Mashpriborintorg on July 16, 2015, 05:43:05 amI'll look into how easily I can get replacement paper for the scriber and I'll definitely steal at least the power resistor from the oven. I don't think I see anything else that useful-looking however: as pretty as things like the plumbing are I'll just have them sitting around doing nothing.

author: PedroDaGr8
author_rank: Super Contributor
timestamp: July 17, 2015, 03:38:16 pm
content: Quote from: Whales on July 17, 2015, 01:43:21 pmYes, many times. Not this specific model but ones just like it and even older. These types are often used in undergraduate labs because they are VERY damn robust.In the modern era, GCs by themselves are seldom used. They are typically coupled to some other analytical device such as a mass spectrometer, commonly referred to as a GCMS. These are MUCH MUCH higher end devices. The columns on these are often 30-50m+ in length and the diameter of a fiber optic cable.The compounds coming off the GC are fed into a mass spectrometer giving additional information about the chemicals being eluted. Here is a common model of GCMS.

author: SeanB
author_rank: Super Contributor
timestamp: July 18, 2015, 09:48:38 am
content: Your chart paper is actually thermal paper, like that used in till receipts. The write head has a heater, to get it hot. There is a 3VAC supply and a 10R wirewound pot on the side of the print mech to adjust the heat to set it for the write speed of the paper.You can use standard thermal till rolls inside it if you get one the right width. That chart recorder unit was made as single, dual or 4 head versions, using a small rotary motor to drive the write head with a bipolar current source on one of the boards, I did take one apart a while ago, still have the motors and drivers.

author: Ian.M
author_rank: Super Contributor
timestamp: July 18, 2015, 10:35:13 am
content: I'd scavenge the whole oven with its heater, sensor(s) and preferably the temperature control circuit, even if you have to hack up a PCB to isolate it! A temperature controlled oven is an extremely useful thing to have if you ever get into precision low drift analog stuff. However beware: old thermal insulation may not be asbestos free.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 18, 2015, 01:23:44 pm
content: Heck, if the whole thing still works, it's probably of value to an amateur chemist. A few bucks of junk, but to the right hand, a capable analytical instrument!I wouldn't say regular GC is falling out of favor; I did it in ~2006 in OChem. We had AAS, NMR and a few others, but no GCMS or ICP or any of those fancy things.Main downside is you need to know what the binding capability of your media is (which, as it's identified as molecular sieves, is probably not terrible) in order to get useful results from it.Tim

author: PedroDaGr8
author_rank: Super Contributor
timestamp: July 19, 2015, 01:08:21 am
content: Quote from: T3sl4co1l on July 18, 2015, 01:23:44 pmFalling out of favor is maybe a bad choice of words but it is definitely seldom used by itself. Almost every time I have used it outside of undergrad lab it has been coupled to another detection scheme that gave additional information. The main reason for this is, GC by itself, much like LC, is of limited diagnostic value on its own; retention time can only give you so much information making it mostly useful for samples of relatively known composition. GC, and to some degree LC, serves as an excellent preparatory method for more advanced schemes like MS, tandem MS, AES and ICP. It's main uses are in detecting specific known analytes and for determining purity of compounds. LC has a bit more use, strictly due to its ability for non-destructive sample prep, which is the reason for its various iterations (FPLC, HPLC, UPLC, plain LC, etc.) In most of the labs I worked in, we had at least one old GCMS for sanity checks and reaction monitoring. These were beaters with questionable accuracy (usually the baseline was really high due to the heavy impure samples loaded on but still good enough to monitor reaction progress).

author: ElektroQuark
author_rank: Unknown
timestamp: July 19, 2015, 08:47:51 am
content: Yes. GCMS systems are very good for looking for unknown compounds.We have an Agilent GC (the vertical tower and the GC system at the right of the picture Pedro has posted), without the MS part, but we only use it for PCB analysis.