Hi A thermistor has *no* output unless it is in a circuit that biases it up. A thermocouple is the one that has an output when no bias is present….
Take a 10K thermistor and a 10K resistor and put them in series. You will get roughly Vcc / 2 at 25C at the junction of the two parts.. The output will change about 1.5% per degree. With a 5V Vcc, that’s around 38 mV/C. Bob > On Jun 4, 2017, at 4:49 PM, Donald E. Pauly <trojancow...@gmail.com> wrote: > > 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. _______________________________________________ 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.