analog temperature sensor

The astounding lameness of USENET posts never ceases to amaze me, whether it's beginning product designers asking exceedingly basic questions, or people who should know much better posting snark for snark's sake.

Fortunately, when large concentrations of trash come from one poster, the guy can be plonked.

Bye.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com

How big can it be. I'm using PNP's in TO-220 packs as diode connected tran sistors. A 5 or 10 Volt reference for the current source and an opamp to b oost the voltage... maybe an offset too?) If you can use Fairchild's TIP32 C's, then I can send/post my single point calibration curve.

George H.

I'm not talking about self-heating, I'm talking about inaccuracy due to not measuring what you think you're measuring.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

[and temperature range -20C to 70C]

Are you seeking an electronic component (thing that gets connected with solder), or a probe (thing that has a long wire to the 'box' where its readings are used), or a meter (thing that has a display as well as a scaled analog output)?

Does the sensor have to tolerate weather, kitchen accidents, or inquisitive children?

Can we assume that 24V power is available? If so, there is a plethora of 4-20 mA designs, tested and ready, that can be adapted.

ZNI1000TA is a fun part. It's an isolated 1K nickel RTD in a sot-23 package, where pin 3 is the thermal contact. Nickel resistance bows up, so you can linearize it by loading it with - according to Spehro -

4.206K.

I use that in an analog realtime mosfet SOAR computer shutdown thing.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Yowza, 600 K/W theta_JA. That's a factor of three worse than a TO92, even.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

That's good! What matters is theta from the tab to the nickel element, which I presume is lower than the 600.

It wouldn't be difficult to measure with, say, the tab soldered to a chunk of copper.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

That would be great, if true. The data sheet doesn't give much cause for optimism, though, does it?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

Given that it's a temperature sensor, the data sheet is pitiful.

The average SOT23, soldered to a PCB, is generally under 300 K/w, so I surmise that they measured this part, at about 600, truly in free air.

I like this part. Don't spoil it for me. Or, worse, force me to actually measure it.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Your wish is my command. ;)

Cheers

Phil "hired gun" Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

Oh, measure it for me then. I like little npn/pnp power transistors. (you have to make at least one calibration measurement, which is a pain.)

George H.

I wonder how consistant a small transistor would be as a temperature sensor, uncalibrated per unit.

This nickel RTD would be fairly easy to measure for Theta-jx, since it's simultaneously a heater and a thermometer. [1]

Transistors and mosfets and diodes can do that too, be a heater and a thermometer to measure their own junction temp, but the functions usually have to be time-shared.

I like the Zetex thing because it's electrically isolated and pretty well calibrated. We solder the tab onto the drain of a mosfet (on the same copper pour, close to the fet) to get the base temp for our SOAR calculation.

[1] but I'm still not going to do it!

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

Hmm I could generate some numbers ~100 measured, there's ~ +/- 5mV max. offset at room temp. +/- 2mV might be typical (~2mV/K) Out of 100 I rejected one for being "out of bounds". One is not very good statistics... it was clearly out of bounds.

I don't know if looking at the delta V vs delta I, would help or not... I like one "real" temperature measurement.

No problem, (what sort of temperature accuracy?.. OK I should look up the data sheet.)

George H.

There is a TO-220 version of the LM35. Nice for measuring the temp of heat sinks.

--

John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

That said, nothing beats a thermocouple for low thermal mass (and ruggedness). You can use an AWG40 thermocouple for speed or and AWG30 T/C that will still work after you pound it with a hammer.

Thermocouples measure (essentially) the difference between the temperature at two points, so you need to measure the temperature at the reference junction (called, for historical reasons, the 'cold junction') **more** accurately than your desired overall system accuracy. So you're into two sensors. If you can measure the desired temperature well enough with the cold junction sensor (range, speed and physical constraints) then you don't need the thermocouple at all.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward" 
speff@interlog.com             Info for manufacturers: http://www.trexon.com 
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

LM19 or TMP36, and the op-amp - those are both 2.4V parts

--
umop apisdn

On a sunny day (Mon, 6 Oct 2014 11:34:40 -0700 (PDT)) it happened George Herold wrote in :

As J.L. says, LM35 is OK. I am using it as reference for environment temp in my thermocouple interface.

In such a case the fact that the leads temperature have an effect on the result does not matter, as leads are at environment too. The LM35 is readable in degrees C directly...

Anyways, with that thermocouple interface you can have almost any temp range you want.

You can also use a simple PIC to measure temperature directly, Microchip has an application note for that, and then directly output the temperature via RS232

Needs calibrating though.

And yes, simple diode works well, but also needs calibration.

I have used the LM35 outside too, in a sealed plastic tube, with several meters wire, works OK.

Here is a temperature to voltage - and reverse conversion program for several thermocouple types:

The OP should specify range and accuracy, other things, measuring temperature at the sun's corona can be difficult. this brings us to optical methods.

For simple applications the finger can be used, and you write the estimated temperature directly on paper... In the same way voltage, pressure, humidity data can be obtained.

dah dah :-)

I use a thinfilm 1K platinum RTD outdoors:

It's in a plastic straw, epoxy filled, RG174 coax, accurate to better than 0.2 C.

I don't trust LM35s for outdoor use. They don't drive cable capacitance well, and noise spikes can make them latch up. NEVER run them at over 5 volts; negative pulldown, for below 0C, is risky.

I'm pretty good at estimating temperatures from 50 to 60C, based on how long I can keep my finger on a surface.

--

John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

On a sunny day (Tue, 07 Oct 2014 02:34:57 -0700) it happened John Larkin wrote in :

Correction, using the LM135, basically same thing, but used with only 2 wires. It behaves much like a zener.

No bad polls, great!

The LM135 does that very well, I decoupled mine with some nF so my transmitter does not cause false readings. Only 2 wires needed (leave adj input disconnected).