This is not a Pirani gauge Tube.  What is it?   - Page 1
Forum section: electronics / general

author: jpanhalt
author_rank: Super Contributor
timestamp: November 25, 2022, 07:36:31 pm
content: My Pirani gauge tube (Fredericks brand Televac) burned out last week, so I went to eBay. A kind seller had "two." One was used and the other had no visible signs of use. The price was good, and I bit. The used tube worked fine. The "new" tube didn't. In fact, when tested for pinout, it was completely different. A slight twist of the brass end unscrewed. I had never seen a Fredericks Pirani gauge tube that could be opened. There was an O-ring seal, a ceramic PCB, what looked like an IC, and one pin was soldered to a brass tube (see attached picture).My guess is that someone at Sandia (Albuquerque) used a new Fredericks Pirani body to make something different, like an ion gauge. I could find no evidence of a filament, though. The quality of the machining is very nice, so I am assuming a professional instrument shop did it. The seller is in Santa Fe, NM, and I have asked him whether he got it there.Any ideas what it is?John

author: TimFox
author_rank: Super Contributor
timestamp: November 25, 2022, 08:04:41 pm
content: Could it be a home-brew thermistor (or possibly thermocouple) gauge, which measures thermal conduction to obtain pressure?If from Santa Fe, it could also have been made at Los Alamos laboratory.

author: jpanhalt
author_rank: Super Contributor
timestamp: November 25, 2022, 08:33:25 pm
content: The brass tube has only a single wire to it. The flared end is attached to the ceramic PCB. The "IC" is on the opposite side. With a bright light down the tube, I cannot see any opening -- only the white of the ceramic. I am assuming that attachment is just a mechanical fixture. That single electrical connection is what me think of some sort of ion sensor. I see no evidence of any TC or heater wire, unless they are buried in the epoxy brick I am calling an IC. Pirani/TC gauge tubes from Fredericks are constructed much like an old incandescent bulb. Each of the 4 pins is connected to the end of a filament connected to an opposing pin. The two loops of filament are connected at about their midpoints.Los Alamos is another option. I mention Sandia as we did some work with it years ago.

author: coppercone2
author_rank: Super Contributor
timestamp: November 25, 2022, 09:23:51 pm
content: oh, thats a picard gauge

author: jpanhalt
author_rank: Super Contributor
timestamp: November 26, 2022, 11:37:03 am
content: UPDATEAfter a little sleep, I examined the chip and was able to decipher LX1602A and a strange poorly defined logo. That part number led to Honeywell pressure transducers and this:https://www.datasheets.com/en/part-details/lx1602a-honeywell-34515327#datasheetSorry for that link to archive; I could not find the datasheet easily on the Honeywell site. A 1977 booklet by Honeywell does show the internals and that attached logo, which is consistent with the logo on the chip.Working hypothesis is that someone took a lot of effort to gut an LX1602A and put it inside the brass body of a Fredericks gauge. I will be testing it later as the setup is quite simple -- only 3 leads (GND, V(excitation), and V(output)). The connection to the cylinder is probably a ground too. Notably, the actual sensor in the transducer is a ceramic disk, which might be what I saw. Will report when I have another update.

author: artag
author_rank: Super Contributor
timestamp: November 26, 2022, 12:31:00 pm
content: That logo is National Semiconductor Corp (now part of TI). It's a heavily stylized 'NS'. It was used in the '80s (I have an example from 1988). There have been at least a couple of other logos since, evolving from the wave to a curve to a circle.https://www.graphis.com/logos/24865fee-4b41-11e2-ae70-f23c91dffdec/I have a few pressure transducers from the same source, also NS. They were available in both packaged (diecast housing) and unpackaged (ceramic substrate) forms.I thought I had an NS data book too, but it turned out to be Sensym 'Pressure transducer handbook' from 1983, as your honeywell link also indicates. It's really more of an application handbook than a data book. So it appears the LX series were owned by at least Sensym, National Semi and Honeywell - though I have no clue about the timeline if your data was from 1977. The handbook mentions only Sensym and Sensortec Gmbh, nothing about honeywell or NS.

author: jpanhalt
author_rank: Super Contributor
timestamp: November 26, 2022, 03:08:07 pm
content: Mystery Solved:It's an absolute pressure gauge (0-15 psia) based on the LX1602A chip. It works. Pinout to the octal base (FWIW) is:Pin1 = VePin2 = VpPin3 = GNDPin4 = NCPin5 = brass tube (NC to the chip)My guess since it came from a research lab (seller wasn't sure which one) was that it was used either for measuring pressures greater than a few Torr or adding a specific gas to something at a known pressure.

author: TimFox
author_rank: Super Contributor
timestamp: November 26, 2022, 05:22:23 pm
content: The last posts reminded me of a version of that National transducer that came packaged in metal with a small tube for the inlet.In grad school (late 1970s), we used one (I don't remember the pressure range) where the shop brazed a suitable fitting to that tube for our lab.

author: jpanhalt
author_rank: Super Contributor
timestamp: December 26, 2022, 01:32:07 pm
content: UPDATEThis was the perfect project for spending the Christmas holiday bored and with very cold (for us) weather.Based on the datasheet, I built an op-amp circuit to convert sensor's output of about 2.5 ±0.5 V to 10.7V to something my little PIC12F1840 could convert to 0V to 5V. The ratio of voltage to psi (absolute) is about 670 ±13 mV/psi. I added a couple of trimmer resistors to handle variation between devices. My device "zeros" at 2.6V.In summary, I built a gold shovel without a handle. Attached are several files to illustrate that effort:1) LTSpice simulation2) Real hardware (Rigol) output that shows pretty good agreement with the simulation (yellow = applied signal, blue = op-amp output)3) Schematic (Eagle)4) Breadboard layout (Eagle)5) LCD display of the raw voltage. I probably won't waste time converting it to psia.6) A view of the completed breadboard

author: jpanhalt
author_rank: Super Contributor
timestamp: January 08, 2023, 02:53:04 pm
content: UPDATE2I decided to finish the project by actually writing code to display results on a Parallax 2x16 LCD. Of course any similar LCD that accepts RS232-like serial ASCII will work.I am also going to try to upload a video. My apologies in advance. It is my first attempt with Windows movie maker using a brand new camera that I haven't learned how to force manual focus on yet.It appears I need more study on the subject. Can't upload wlmp files. Will work on converting the native .mov file to some acceptable format.EDIT: It looks like my question about adding video in another thread will take a time to get a response. I want to put this project to bed. So, here is a still image of a single reading. Those readings progress linearly with a linear slope input.Now for some practical use. I have considered storing my Kester solder paste under high vacuum in a refrigerator, but maybe storing that paste under a reduced atmosphere, say 5 psia, in dry argon would be better. This dinosaur gauge would make doing that easy. Any thought on that?

author: rdl
author_rank: Super Contributor
timestamp: January 09, 2023, 03:56:15 pm
content: It's not clear exactly what problems you're having with the video files. This may be no help at all, but the most common container files I see are .mp4 and .mkv, the actual encoding used varies but H.264 and H.265 are common. The program Handbrake is pretty good at converting most video files from one format to another.https://handbrake.fr/

author: jpanhalt
author_rank: Super Contributor
timestamp: January 09, 2023, 05:30:58 pm
content: Here's list of supported files at EEVBlog:QuoteNone of the video formats I tried worked.

author: pardo-bsso
author_rank: Frequent Contributor
timestamp: January 09, 2023, 05:39:38 pm
content: Quote from: jpanhalt on January 09, 2023, 05:30:58 pmCan you upload the file somewhere so we can take a look and see why it's not being accepted?

author: jpanhalt
author_rank: Super Contributor
timestamp: January 09, 2023, 06:10:03 pm
content: It is not being accepted, because the extension (i.e., .mov, .avi, .wlmp, or .MP4 ) is not one of the allowed types.

author: pardo-bsso
author_rank: Frequent Contributor
timestamp: January 10, 2023, 01:08:06 am
content: My bad, I didn't ask properly.My question was aimed at if you could upload the file somewhere else (dropbox, personal site, etc.) so we can take a look and see how to help you.

author: jpanhalt
author_rank: Super Contributor
timestamp: January 10, 2023, 02:15:56 am
content: Well that was my question is another thread, but it has had no replies.https://www.eevblog.com/forum/chat/uploading-video/msg4626013/#msg4626013Do you have any advice for a site to host it? After reading a review of about 10 sites, I am leaning towards Vimeo.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 10, 2023, 05:41:01 am
content: The usual trick to get around the extension restrictions is to either zip the file, or just rename it with something allowed like .pdf. If you go the renaming route you have to explain the correct extension in the text to allow those who download to rename it properly.I am not sure of why Dave restricts the extensions. Usually this is to limit people passing file types which are notorious for spreading malware, but several of the allowed file types are among those considered risky when this process started on web sites sometime back around 2000. Be good about this and don't abuse the technique.