I own several Fluke 52 stereo thermometers with K themocouples. They run 40 μV/C°. All thermistors have tiny outputs without op amps. They also suffer from self heating. AD590 sensors give AT LEAST 15 mV/C° without op amps. If a regulated 3,000V supply is available they can give 2 V/C° into a 1 Watt 10 Meg resistor.
πθ°μΩω±√·Γλ WB0KVV ---------- Forwarded message ---------- From: Bob kb8tq <kb...@n1k.org> Date: Sun, Jun 4, 2017 at 11:46 AM Subject: Re: [time-nuts] HP5061B Versus HP5071 Cesium Line Frequencies To: Discussion of precise time and frequency measurement <time-nuts@febo.com> Cc: "rwa...@aol.com" <rwa...@aol.com>, "Donald E. Pauly" <trojancow...@gmail.com> Hi I think you have thermistors and thermocouples a bit mixed up. You can get quite substantial output voltages from a thermistor bridge…. Bob > On Jun 4, 2017, at 11:44 AM, Donald E. Pauly <trojancow...@gmail.com> wrote: > > I stand by my remark that thermistors have been obsolete for over 40 > years. The only exception that I know of is cesium beam tubes that > must withstand a 350° C bakeout. Thermistors are unstable and > manufactured with a witches brew straight out of MacBeth. Their > output voltages are tiny and are they inconvenient to use at different > temperatures. > > Where did you get the idea to use a 1 k load for an AD590? If you run > it from a -5 V supply you can use a 15 k load to a +5V supply. This > gives 15 V/C° output. If you drive it from a 10 Meg impedance current > source, you get 30,000 V/ C°. If I remember correctly, I drove a > power MOSFET heater gate directly in my prototype oven 20 years ago. > It would go from full off to full on in 1/15 ° C. Noise is 1/25,000 ° > C in a 1 cycle bandwidth. > > The room temperature coefficient of an AT crystal is -100 ppb per > reference cut angle in minutes. (-600 ppb/C° for standard crystal) > The practical limit in a crystal designed for room temperature is > about 0.1' cut accuracy or ±10 ppb/C°. If you have access to an > atomic standard, you can use feed forward to get ±1 ppb/C°. If the > temperature can be held to ±0.001° C, this is ±1 part per trillion. > This kind of accuracy has never been heard of. Feed forward also > allows you to incorporate the components of the oscillator into the > thermal behavior. It does no good to have a perfect crystal if the > oscillator components drift. > > πθ°μΩω±√·Γλ > WB0KVV > > ---------- Forwarded message ---------- > From: jimlux <jim...@earthlink.net> > Date: Sun, Jun 4, 2017 at 4:47 AM > Subject: Re: [time-nuts] Fwd: HP5061B Versus HP5071 Cesium Line Frequencies > To: time-nuts@febo.com > > > On 6/3/17 9:56 PM, Donald E. Pauly wrote: > >> It was only in the early 70s that Analog Devices invented the AD590 >> solid state temperature sensor. It made thermister bridges obsolete. > > > There is a difference between something like a platinum resistance > thermometer (PRT or RTD) and a thermistor, but they both are "measure > resistance to measure temperature" devices. > > Yes, the AD590 is a useful part (I've got some in a device being > launched in August), but PRTs,thermistors, and thermocouples are still > widely used. > > I don't know that the inherent precision (at room temperature)of the > various techniques is wildly different. A 1mV/K signal (AD590 into a > 1k resistor) has to be measured to 0.1mV for 0.1 degree accuracy. > That's out of 300mV, so 1 part in 3000 > > A type E thermocouple is 1.495 mV at 25C and 1.801 at 30C, so about > 0.06 mV/K slope. Measure 0.006mV for 0.1 degree (plus the "cold > junction" issue). 1 part in 250 measurement. > > Modern RTDs all are 0.00385 ohm/ohm/degree at 25C. Typically, you > have a 100 ohm device (although there are Pt1000s), so it's changing > 0.385 ohm/degree. 1 part in 3000 > > Checking the Omega catalog.. A 44007 has nominal 5k at 25C, and is > 4787 at 26C, so 1 part in 24. > > Especially these days, with computers to deal with nonlinear > calibration curves, there's an awful lot of TCs and Thermistors in > use. The big advantage of the AD590 and PRT is that they are basically > linear over a convenient temperature range. > > In a variety applications, other aspects of the measurement device are > important - ESD sensitivity, tolerance to wildly out of spec > temperature without damage, radiation effects etc. Not an issue here, > but I'll note that the thermistor, PRT, and thermocouple are > essentially ESD immune. The AD590 most certainly is not. > > If you go out and buy cheap industrial PID temperature controller it > will have input modes for various thermocouples and PRTs. I suppose > there's probably some that take 1uA/K, but it's not something I would > expect. > > So I wouldn't say thermistor bridges (or other temperature > measurements) are obsolete. > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.