On Tuesday, June 27, 2017 at 4:42:58 PM UTC-4, John Larkin wrote:> On Tue, 27 Jun 2017 13:34:07 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote: > > >On Tuesday, June 27, 2017 at 3:59:08 PM UTC-4, John Larkin wrote: > >> On Tue, 27 Jun 2017 12:41:18 -0700 (PDT), George Herold > >> <gherold@teachspin.com> wrote: > >><big snip>> >> >> >> How accurate do you need it to be? > >> >> >Right, one degree (C or K) is plenty good for most things. > >> >> >Resolution, and changes in temperature are more important. > >> >> > > >> >> >George H. > >> >> >*I've got a calibrated diode from lakeshore, which is my temperature > >> >> >'standard'. I tack that onto the transistor. > >> >> > >> >> Cryo stuff? > >> >Right, 77- 400 K. The diode connected transistor is going to > >> >'crap out' somewhere below 77 K. Well it will still be a diode > >> >but no 'gain' from the collector. > >> > >> 77K should be OK. Bipolar devices, transistors and diodes, go to hell > >> below around 20K. > >> > >> Lakeshore has some magical recipe that makes repeatable temperature > >> measurement diodes at liquid helium temps, but it's not easy. Other > >> people have messed up at this. > >Hmm OK, I have no liquid helium here. So I can't do tests below 77K. > >It'd be fun to look at commercial diodes at low temps... maybe find > >one that works. (Is there really a special sauce at Lakeshore?) > > > >George H. > > Below 20K, diode voltage drop skyrockets (to, like, volts at a couple > K) and things get ohmic. Apparently it's erratic on doping or > something, because other people have tried to compete with Lakeshore > and every batch was different.Yeah I'd figure there should have been plenty of people trying to make one work, given the price Lakeshore charges. So a project most likely to fail. Below 20K where are the charge carriers coming from? Very shallow impurities? You could shine a little light on the junction to make carriers.. that's kinda cheating. George H.> > We did the cryo instrumentation for the Jlabs/CEBAF machine, and for > the helium liquefaction plant for the Supercollider (which may still > be there.) > > > -- > > John Larkin Highland Technology, Inc > picosecond timing precision measurement > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
Zenering a big transistor
Started by ●June 26, 2017
Reply by ●June 28, 20172017-06-28
Reply by ●June 28, 20172017-06-28
On Wed, 28 Jun 2017 07:40:26 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:>On Tuesday, June 27, 2017 at 4:42:58 PM UTC-4, John Larkin wrote: >> On Tue, 27 Jun 2017 13:34:07 -0700 (PDT), George Herold >> <gherold@teachspin.com> wrote: >> >> >On Tuesday, June 27, 2017 at 3:59:08 PM UTC-4, John Larkin wrote: >> >> On Tue, 27 Jun 2017 12:41:18 -0700 (PDT), George Herold >> >> <gherold@teachspin.com> wrote: >> >> ><big snip> >> >> >> >> How accurate do you need it to be? >> >> >> >Right, one degree (C or K) is plenty good for most things. >> >> >> >Resolution, and changes in temperature are more important. >> >> >> > >> >> >> >George H. >> >> >> >*I've got a calibrated diode from lakeshore, which is my temperature >> >> >> >'standard'. I tack that onto the transistor. >> >> >> >> >> >> Cryo stuff? >> >> >Right, 77- 400 K. The diode connected transistor is going to >> >> >'crap out' somewhere below 77 K. Well it will still be a diode >> >> >but no 'gain' from the collector. >> >> >> >> 77K should be OK. Bipolar devices, transistors and diodes, go to hell >> >> below around 20K. >> >> >> >> Lakeshore has some magical recipe that makes repeatable temperature >> >> measurement diodes at liquid helium temps, but it's not easy. Other >> >> people have messed up at this. >> >Hmm OK, I have no liquid helium here. So I can't do tests below 77K. >> >It'd be fun to look at commercial diodes at low temps... maybe find >> >one that works. (Is there really a special sauce at Lakeshore?) >> > >> >George H. >> >> Below 20K, diode voltage drop skyrockets (to, like, volts at a couple >> K) and things get ohmic. Apparently it's erratic on doping or >> something, because other people have tried to compete with Lakeshore >> and every batch was different. > >Yeah I'd figure there should have been plenty of people trying to make >one work, given the price Lakeshore charges. So a project most likely >to fail. > >Below 20K where are the charge carriers coming from? >Very shallow impurities? >You could shine a little light on the junction to make carriers.. that's >kinda cheating. > >George H.I wanted to use a tuning-fork quartz crystal as a cryo temp sensor, but I couldn't get my customer (who had the facilities to help develop it) interested. They stuck with the Lakeshore diodes, lots of them. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●June 28, 20172017-06-28
On Wednesday, June 28, 2017 at 11:30:08 AM UTC-4, John Larkin wrote:> On Wed, 28 Jun 2017 07:40:26 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote: > > >On Tuesday, June 27, 2017 at 4:42:58 PM UTC-4, John Larkin wrote: > >> On Tue, 27 Jun 2017 13:34:07 -0700 (PDT), George Herold > >> <gherold@teachspin.com> wrote: > >> > >> >On Tuesday, June 27, 2017 at 3:59:08 PM UTC-4, John Larkin wrote: > >> >> On Tue, 27 Jun 2017 12:41:18 -0700 (PDT), George Herold > >> >> <gherold@teachspin.com> wrote: > >> >> > ><big snip> > >> >> >> >> How accurate do you need it to be? > >> >> >> >Right, one degree (C or K) is plenty good for most things. > >> >> >> >Resolution, and changes in temperature are more important. > >> >> >> > > >> >> >> >George H. > >> >> >> >*I've got a calibrated diode from lakeshore, which is my temperature > >> >> >> >'standard'. I tack that onto the transistor. > >> >> >> > >> >> >> Cryo stuff? > >> >> >Right, 77- 400 K. The diode connected transistor is going to > >> >> >'crap out' somewhere below 77 K. Well it will still be a diode > >> >> >but no 'gain' from the collector. > >> >> > >> >> 77K should be OK. Bipolar devices, transistors and diodes, go to hell > >> >> below around 20K. > >> >> > >> >> Lakeshore has some magical recipe that makes repeatable temperature > >> >> measurement diodes at liquid helium temps, but it's not easy. Other > >> >> people have messed up at this. > >> >Hmm OK, I have no liquid helium here. So I can't do tests below 77K. > >> >It'd be fun to look at commercial diodes at low temps... maybe find > >> >one that works. (Is there really a special sauce at Lakeshore?) > >> > > >> >George H. > >> > >> Below 20K, diode voltage drop skyrockets (to, like, volts at a couple > >> K) and things get ohmic. Apparently it's erratic on doping or > >> something, because other people have tried to compete with Lakeshore > >> and every batch was different. > > > >Yeah I'd figure there should have been plenty of people trying to make > >one work, given the price Lakeshore charges. So a project most likely > >to fail. > > > >Below 20K where are the charge carriers coming from? > >Very shallow impurities? > >You could shine a little light on the junction to make carriers.. that's > >kinda cheating. > > > >George H. > > I wanted to use a tuning-fork quartz crystal as a cryo temp sensor, > but I couldn't get my customer (who had the facilities to help develop > it) interested. They stuck with the Lakeshore diodes, lots of them.Huh, the 32kHz ones? Aren't they made to have a low Temp-co? I guess away from room temp they would change more. They'd have to live in vacuum or the liquid helium might change the frequency. Most people are afraid to try something new... better the devil you know. George H.> > > > > -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronics
Reply by ●June 28, 20172017-06-28
On Tuesday, June 27, 2017 at 5:19:16 PM UTC-4, tom wrote:> "George Herold" <gherold@teachspin.com> wrote in message > news:19ba65c7-d8d1-4a14-9e82-ae7dac32a491@googlegroups.com... > On Tuesday, June 27, 2017 at 3:59:08 PM UTC-4, John Larkin wrote: > > On Tue, 27 Jun 2017 12:41:18 -0700 (PDT), George Herold > > <gherold@teachspin.com> wrote: > > > > >On Tuesday, June 27, 2017 at 3:32:48 PM UTC-4, John Larkin wrote: > > >> On Tue, 27 Jun 2017 11:49:51 -0700 (PDT), George Herold > > >> <gherold@teachspin.com> wrote: > > >> > > >> >On Tuesday, June 27, 2017 at 12:51:20 PM UTC-4, John Larkin wrote: > > >> >> On Tue, 27 Jun 2017 09:12:14 -0700 (PDT), George Herold > > >> >> <gherold@teachspin.com> wrote: > > >> >> > > >> >> >On Tuesday, June 27, 2017 at 10:02:22 AM UTC-4, John Larkin wrote: > > >> >> >> On Mon, 26 Jun 2017 18:02:21 -0700 (PDT), > > >> >> >> dagmargoodboat@yahoo.com > > >> >> >> wrote: > > >> >> >> > > >> >> >> >On Monday, June 26, 2017 at 8:17:45 PM UTC-4, > > >> >> >> >dagmarg...@yahoo.com wrote: > > >> >> >> >> On Monday, June 26, 2017 at 5:33:47 PM UTC-4, John Larkin > > >> >> >> >> wrote: > > >> >> >> >> > On Mon, 26 Jun 2017 14:21:43 -0700 (PDT), > > >> >> >> >> > dagmargoodboat@yahoo.com > > >> >> >> >> > wrote: > > >> >> >> >> > > > >> >> >> >> > >On Monday, June 26, 2017 at 1:15:44 PM UTC-4, John Larkin > > >> >> >> >> > >wrote: > > >> >> >> >> > >> On Mon, 26 Jun 2017 10:04:35 -0700 (PDT), > > >> >> >> >> > >> dagmargoodboat@yahoo.com > > >> >> >> >> > >> wrote: > > >> >> >> >> > >> > > >> >> >> >> > >> >On Monday, June 26, 2017 at 12:59:50 PM UTC-4, > > >> >> >> >> > >> >dagmarg...@yahoo.com wrote: > > >> >> >> >> > >> >> On Monday, June 26, 2017 at 11:51:45 AM UTC-4, George > > >> >> >> >> > >> >> Herold wrote: > > >> >> >> >> > >> >> > I'm using a TIP31C (pnp in to-220 pac) as a temp > > >> >> >> >> > >> >> > sensor (diode connected) > > >> >> >> >> > >> >> > There's a couple of depletion fets in series as > > >> >> >> >> > >> >> > current limiters. (LND150) > > >> >> >> >> > >> >> > The b-e junction starts to zener at ~30 V (only two > > >> >> >> >> > >> >> > tested so far). > > >> >> >> >> > >> >> > So I've got ~1.5 mA flowing at 30 V. Is this going > > >> >> >> >> > >> >> > to damage the junction? > > >> >> >> >> > >> >> > Will it take time? I'm going to measure forward > > >> >> >> >> > >> >> > voltage again after > > >> >> >> >> > >> >> > zenering for 15 minutes. Should I measure something > > >> >> >> >> > >> >> > else too? > > >> >> >> >> > >> >> > > > >> >> >> >> > >> >> > TIA > > >> >> >> >> > >> >> > > > >> >> >> >> > >> >> > George H. > > >> >> >> >> > >> >> > > >> >> >> >> > >> >> Why not just protect your TIP31C from zenering? A few > > >> >> >> >> > >> >> diodes would do it. > > >> >> >> >> > >> >> > > >> >> >> >> > >> > > > >> >> >> >> > >> >e.g., > > >> >> >> >> > >> > | > > >> >> >> >> > >> > +----. > > >> >> >> >> > >> > | | > > >> >> >> >> > >> >TIP31C |<' --- > > >> >> >> >> > >> > .---| ^ D1 > > >> >> >> >> > >> > | |\ | > > >> >> >> >> > >> > | | | > > >> >> >> >> > >> > '-----+----' > > >> >> >> >> > >> > | > > >> >> >> >> > >> > | > > >> >> >> >> > >> > > > >> >> >> >> > >> >Add a zener in series with D1 if you need to stand off > > >> >> >> >> > >> >some reverse voltage. > > >> >> >> >> > >> > > > >> >> >> >> > >> >Cheers, > > >> >> >> >> > >> >James Arthur > > >> >> >> >> > >> > > >> >> >> >> > >> Or use the c-b junction instead. > > >> >> >> >> > > > > >> >> >> >> > >That loses the transistor action, degrading its > > >> >> >> >> > >temperature-sensing > > >> >> >> >> > >performance. > > >> >> >> >> > > > > >> >> >> >> > >Cheers, > > >> >> >> >> > >James Arthur > > >> >> >> >> > > > >> >> >> >> > Think so? It's still a diode with a roughly -2 mV/K tempco. > > >> >> >> >> > > >> >> >> >> I read that ages ago, in an early article about using Motorola > > >> >> >> >> transistors > > >> >> >> >> specifically spec'd as temperature sensors IIRC. (It's amazing > > >> >> >> >> I can > > >> >> >> >> remember that. Still have the article somewhere, I'm sure.) > > >> >> >> >> > > >> >> >> >> > No transistor will ever be a super-accurate temp sensor. > > >> >> >> >> > > >> >> >> >> Delta Vbe is good pretty easily to +/-1oC, uncalibrated. > > >> >> >> >> > > >> >> >> >> > There is an LM35 available in TO220. > > >> >> >> >> > > > >> >> >> >> > Zetex makes a cool 1K ohm SOT23 nickel RTD too. Nickel is > > >> >> >> >> > cool because > > >> >> >> >> > the curve slopes up, so you can linearize it by just loading > > >> >> >> >> > it. RTDs > > >> >> >> >> > are tough and don't rectify RF or oscillate. > > >> >> >> >> > > >> >> >> >> Can't argue with RTDs... > > >> >> >> >> > > >> >> >> >This has interesting measurements of a variety of vendors' > > >> >> >> >2n3904's: > > >> >> >> > > > >> >> >> >http://ww1.microchip.com/downloads/en/AppNotes/00001838A.pdf > > >> >> >> > > > >> >> >> > "Figure 2 also shows why true 2-terminal discrete diodes > > >> >> >> > are not used in temperature sensing applications instead > > >> >> >> > of 3-terminal devices such as the 2N3904. > > >> >> >> > > > >> >> >> > A discrete 2-terminal diode, ideally, would perform in > > >> >> >> > temperature sensing applications as well as a thermal > > >> >> >> > diode would. However, characterization in the labs > > >> >> >> > determined that discrete 2-terminal diodes typically > > >> >> >> > have an ideality factor much higher (1.2-1.5) than > > >> >> >> > ? ASSUMED of 1.004. This discrepancy (between ? ASSUMED > > >> >> >> > and ? REAL) would cause unacceptable temperature > > >> >> >> > measurement errors at all temperatures." > > >> >> >> > > >> >> >> "Unacceptable" is arbitrary and judgemental. It's kinda prissy, > > >> >> >> going > > >> >> >> around assuming stuff. > > >> >> >> > > >> >> >> > > > >> >> >> >I just read a number delta Vbe app notes; all recommend > > >> >> >> >diode-connected > > >> >> >> >transistors over diodes. > > >> >> >> > > > >> >> >> >Cheers, > > >> >> >> >James Arthur > > >> >> >> > > >> >> >> I don't care about ideality factor, how well a c-b junction might > > >> >> >> match some theoretical ideal-diode equation. What matters is how > > >> >> >> well > > >> >> >> you calibrate the V-T curve of a device, and how similar later > > >> >> >> devices > > >> >> >> might be. > > >> >> > > > >> >> >I sorta agree, If I could find a diode that was repeatable and > > >> >> >easily > > >> >> >calibrated against some standard that would be fine. > > >> >> > > >> >> Buy the transistors from the same vendor, no matter how you process > > >> >> the signals. Ideally, but a reel that's a lifetime supply. > > >> >> > > >> >> Seems to me that you can't avoid some actual temperature > > >> >> measurements, > > >> >> unless you buy an IC or an RTD that has guaranteed specs. > > >> >> > > >> >> > > >> >> > > > >> >> >The one nice thing about the 'ideal' behavior is that you can check > > >> >> >the > > >> >> >calibration (very roughly) by looking at the signal as a function > > >> >> >of bias > > >> >> >current. That nice.. and also nice physics. > > >> >> > > > >> >> >George h. > > >> >> > > >> >> In your production units, are you planning to do the theoretical > > >> >> delta-I/deltaV math, or are you just going to use a constant current > > >> >> and measure the diode voltage drop? > > >> >For production, I measure a temperature* and a voltage drop at CC. > > >> >And then generate a table of V vs T. > > >> >I tell them about the delta I/ delta V thing.. I'm guessing most > > >> >everyone > > >> >just ignores it, it's only EE geek types that like that kind of thing. > > >> >> > > >> >> How accurate do you need it to be? > > >> >Right, one degree (C or K) is plenty good for most things. > > >> >Resolution, and changes in temperature are more important. > > >> > > > >> >George H. > > >> >*I've got a calibrated diode from lakeshore, which is my temperature > > >> >'standard'. I tack that onto the transistor. > > >> > > >> Cryo stuff? > > >Right, 77- 400 K. The diode connected transistor is going to > > >'crap out' somewhere below 77 K. Well it will still be a diode > > >but no 'gain' from the collector. > > > > 77K should be OK. Bipolar devices, transistors and diodes, go to hell > > below around 20K. > > > > Lakeshore has some magical recipe that makes repeatable temperature > > measurement diodes at liquid helium temps, but it's not easy. Other > > people have messed up at this. > Hmm OK, I have no liquid helium here. So I can't do tests below 77K. > It'd be fun to look at commercial diodes at low temps... maybe find > one that works. (Is there really a special sauce at Lakeshore?) > > George H. > > > > > > -- > > Pull a vacuum on the LN2 and it will go colder than 77K.Right ~65K or something like that. I had a friend who did that for an experiment in grad school. He made a big block of solid nitrogen in the dewar.. it took a while to thaw. George H.
Reply by ●June 28, 20172017-06-28
On Wed, 28 Jun 2017 08:45:55 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:>On Wednesday, June 28, 2017 at 11:30:08 AM UTC-4, John Larkin wrote: >> On Wed, 28 Jun 2017 07:40:26 -0700 (PDT), George Herold >> <gherold@teachspin.com> wrote: >> >> >On Tuesday, June 27, 2017 at 4:42:58 PM UTC-4, John Larkin wrote: >> >> On Tue, 27 Jun 2017 13:34:07 -0700 (PDT), George Herold >> >> <gherold@teachspin.com> wrote: >> >> >> >> >On Tuesday, June 27, 2017 at 3:59:08 PM UTC-4, John Larkin wrote: >> >> >> On Tue, 27 Jun 2017 12:41:18 -0700 (PDT), George Herold >> >> >> <gherold@teachspin.com> wrote: >> >> >> >> ><big snip> >> >> >> >> >> How accurate do you need it to be? >> >> >> >> >Right, one degree (C or K) is plenty good for most things. >> >> >> >> >Resolution, and changes in temperature are more important. >> >> >> >> > >> >> >> >> >George H. >> >> >> >> >*I've got a calibrated diode from lakeshore, which is my temperature >> >> >> >> >'standard'. I tack that onto the transistor. >> >> >> >> >> >> >> >> Cryo stuff? >> >> >> >Right, 77- 400 K. The diode connected transistor is going to >> >> >> >'crap out' somewhere below 77 K. Well it will still be a diode >> >> >> >but no 'gain' from the collector. >> >> >> >> >> >> 77K should be OK. Bipolar devices, transistors and diodes, go to hell >> >> >> below around 20K. >> >> >> >> >> >> Lakeshore has some magical recipe that makes repeatable temperature >> >> >> measurement diodes at liquid helium temps, but it's not easy. Other >> >> >> people have messed up at this. >> >> >Hmm OK, I have no liquid helium here. So I can't do tests below 77K. >> >> >It'd be fun to look at commercial diodes at low temps... maybe find >> >> >one that works. (Is there really a special sauce at Lakeshore?) >> >> > >> >> >George H. >> >> >> >> Below 20K, diode voltage drop skyrockets (to, like, volts at a couple >> >> K) and things get ohmic. Apparently it's erratic on doping or >> >> something, because other people have tried to compete with Lakeshore >> >> and every batch was different. >> > >> >Yeah I'd figure there should have been plenty of people trying to make >> >one work, given the price Lakeshore charges. So a project most likely >> >to fail. >> > >> >Below 20K where are the charge carriers coming from? >> >Very shallow impurities? >> >You could shine a little light on the junction to make carriers.. that's >> >kinda cheating. >> > >> >George H. >> >> I wanted to use a tuning-fork quartz crystal as a cryo temp sensor, >> but I couldn't get my customer (who had the facilities to help develop >> it) interested. They stuck with the Lakeshore diodes, lots of them. > >Huh, the 32kHz ones? Aren't they made to have a low Temp-co?Their TC is parabolic, intended to have the flat spot at human-wrist temperature. At low temps, it's very steep.>I guess away from room temp they would change more. >They'd have to live in vacuum or the liquid helium might >change the frequency.I got some samples of a vacuum-sealed 32KHz tuning-fork crystal, but I never had the facilities to test them. Most people are afraid to try something>new... better the devil you know.They could have at least got some papers to publish! -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●June 28, 20172017-06-28
On Wednesday, June 28, 2017 at 11:59:42 AM UTC-4, John Larkin wrote:> On Wed, 28 Jun 2017 08:45:55 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote: > > >On Wednesday, June 28, 2017 at 11:30:08 AM UTC-4, John Larkin wrote: > >> On Wed, 28 Jun 2017 07:40:26 -0700 (PDT), George Herold > >> <gherold@teachspin.com> wrote: > >> > >> >On Tuesday, June 27, 2017 at 4:42:58 PM UTC-4, John Larkin wrote: > >> >> On Tue, 27 Jun 2017 13:34:07 -0700 (PDT), George Herold > >> >> <gherold@teachspin.com> wrote: > >> >> > >> >> >On Tuesday, June 27, 2017 at 3:59:08 PM UTC-4, John Larkin wrote: > >> >> >> On Tue, 27 Jun 2017 12:41:18 -0700 (PDT), George Herold > >> >> >> <gherold@teachspin.com> wrote: > >> >> >> > >> ><big snip> > >> >> >> >> >> How accurate do you need it to be? > >> >> >> >> >Right, one degree (C or K) is plenty good for most things. > >> >> >> >> >Resolution, and changes in temperature are more important. > >> >> >> >> > > >> >> >> >> >George H. > >> >> >> >> >*I've got a calibrated diode from lakeshore, which is my temperature > >> >> >> >> >'standard'. I tack that onto the transistor. > >> >> >> >> > >> >> >> >> Cryo stuff? > >> >> >> >Right, 77- 400 K. The diode connected transistor is going to > >> >> >> >'crap out' somewhere below 77 K. Well it will still be a diode > >> >> >> >but no 'gain' from the collector. > >> >> >> > >> >> >> 77K should be OK. Bipolar devices, transistors and diodes, go to hell > >> >> >> below around 20K. > >> >> >> > >> >> >> Lakeshore has some magical recipe that makes repeatable temperature > >> >> >> measurement diodes at liquid helium temps, but it's not easy. Other > >> >> >> people have messed up at this. > >> >> >Hmm OK, I have no liquid helium here. So I can't do tests below 77K. > >> >> >It'd be fun to look at commercial diodes at low temps... maybe find > >> >> >one that works. (Is there really a special sauce at Lakeshore?) > >> >> > > >> >> >George H. > >> >> > >> >> Below 20K, diode voltage drop skyrockets (to, like, volts at a couple > >> >> K) and things get ohmic. Apparently it's erratic on doping or > >> >> something, because other people have tried to compete with Lakeshore > >> >> and every batch was different. > >> > > >> >Yeah I'd figure there should have been plenty of people trying to make > >> >one work, given the price Lakeshore charges. So a project most likely > >> >to fail. > >> > > >> >Below 20K where are the charge carriers coming from? > >> >Very shallow impurities? > >> >You could shine a little light on the junction to make carriers.. that's > >> >kinda cheating. > >> > > >> >George H. > >> > >> I wanted to use a tuning-fork quartz crystal as a cryo temp sensor, > >> but I couldn't get my customer (who had the facilities to help develop > >> it) interested. They stuck with the Lakeshore diodes, lots of them. > > > >Huh, the 32kHz ones? Aren't they made to have a low Temp-co? > > Their TC is parabolic, intended to have the flat spot at human-wrist > temperature. At low temps, it's very steep. > > > >I guess away from room temp they would change more. > >They'd have to live in vacuum or the liquid helium might > >change the frequency. > > I got some samples of a vacuum-sealed 32KHz tuning-fork crystal, but I > never had the facilities to test them. > > > > Most people are afraid to try something > >new... better the devil you know. > > > They could have at least got some papers to publish!This is almost impossible to read, but I think they take one down to 4.2 K. http://ieeexplore.ieee.org/document/1537886/ George h.> > > -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronics
Reply by ●July 1, 20172017-07-01
On Wednesday, 28 June 2017 16:59:42 UTC+1, John Larkin wrote:> On Wed, 28 Jun 2017 08:45:55 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote:> >> I wanted to use a tuning-fork quartz crystal as a cryo temp sensor, > >> but I couldn't get my customer (who had the facilities to help develop > >> it) interested. They stuck with the Lakeshore diodes, lots of them. > > > >Huh, the 32kHz ones? Aren't they made to have a low Temp-co? > > Their TC is parabolic, intended to have the flat spot at human-wrist > temperature. At low temps, it's very steep.Do you use 2 with different tempcos & compare f? NT
Reply by ●July 1, 20172017-07-01
On Saturday, July 1, 2017 at 10:04:04 AM UTC-7, tabb...@gmail.com wrote:> On Wednesday, 28 June 2017 16:59:42 UTC+1, John Larkin wrote: > > On Wed, 28 Jun 2017 08:45:55 -0700 (PDT), George Herold > > <gherold@teachspin.com> wrote: > > > >> I wanted to use a tuning-fork quartz crystal as a cryo temp sensor,> > >Huh, the 32kHz ones? Aren't they made to have a low Temp-co?> > Their TC is parabolic, intended to have the flat spot at human-wrist > > temperature. At low temps, it's very steep. > > Do you use 2 with different tempcos & compare f?COTS crystals don't have the tempco you want. This is the one I recall: <https://archive.org/details/Hewlett-Packard_Journal_Vol._16_No._7_1965-03_Hewlett-Packard> The high Q of a quartz oscillator implies small self-heating of the sensor. The aging of quartz means it needs recalibration to stay accurate. So, how do you calibrate a 0.0001 K precision thermometer?
