# IC for temperature measuring with precision of 0.2 degrees C

Status
Not open for further replies.

#### johnyaya

##### Full Member level 2
kty10-5 thermistor circuits

If you can measure resistance I recommend the YSI 44031 thermistor. Good accuracy, 0.1C interchangable, cost about $10 ea. For voltage output I like the Analog Devices AD590M, although it doesn't quite meet your spec (0.5C instead of 0.3C). Analog Devices will sample you one too. #### dkace ##### Full Member level 6 measuring temperatures below freezing with lm35 Looking in the Nationa Semiconductor page, www.national.com, for the ADC0801/ADC0802/..., an A/D converter, in the typical application section , you will find the schemmatics of a temp measurment with LM35 sensor, and instructions of calibration. As I am trying to do this kind of calibration my self, I cann' t help you more right now, but look up there. If you want more , I have the schemmatics and the programm for a thermometer using a μC for the measurement! Hope I helped! #### snowman53 ##### Junior Member level 3 ds18b20 subzero Are you looking for "accuracy", "repeatability" or "sensitivity"? These are three very different concepts that frequently are confused or lumped into a simple requirement for "accuracy" Accuracy: A measure of how close a measurement is to a defined standard - such as the 1990 International Temperature Standard (ITS-90) which uses the freezing or melting points of pure elements to define a standard temperature scale. For example the freezing point of pure gold is 1064.18C. The melting point of pure gallium is 29.7646C. Accuracy is usually not of much concern except for scientific purposes. Repeatability: A measure of how consistently a sensor system records the actual value. Most practical sensors have a "dead band" i.e. they give different results if you approach from above or below the set point. Drift between cal cycles and electronic noise will give you additional repeatability errors. Sensitivity: How much change in sensor output per change in measured value. i.e. 0.1V per degree or 10V per degree, etc. If you need to measure differential, you probably need a high sensitivity sensor with reasonable repeatability. Accuracy is probably not really a concern. For the temperature band you are looking at, a thermistor is a good solution. They can be purchased in a number of configurations from glue on strips to embedded glass beads. And in a number of resistance values that allow you to tailor the sensitivity. Costs are from a few$ to a few hundred \$ depending on the quality you need.

We use thermistors to control temperature difference to +/- 0.001 C (and measure to a decade less) over the range of 0 to 100 C. Accuracy however is only +/- 0.005C & is limited by the standards calibration that is only good to +/- 0.003C. The remaining +/- 0.002C is the sensor and electronics repeatability and drift between cal cycles.

A good way to improve repeatability is to “anneal” the sensor system by cycling it above and below the planned temperature range until the sensor stabilizes.

Hope I have not bored you to death!

#### tranki

##### Newbie level 4
ds1820 repeatability

Thanks for yours explanations snowman53, it's important. The concepts that you explain, at times, are very "mixed" and "confused".

But it's posible that I don't make the question appropriate (my english is not good)
I know that the most suitable sensor for this application, is a pt100 o similar. The question was: Exist in the market an IC with a good stability (repeatability) with good precission for make this aplication?

The sensor is not the problem, I know many types and sizes for the industry. I'm looking for an IC manufactured for this purpose, because is posible to reduce the cost of design. I knows also, diferents conversors for input Pt100 or bi-metal and output in stardard 4-20mA. But I need to reduce the size and cost of circuit. The idea is: Little circuit with microprocessor (8 bits) coneccted with this IC temperature converter, and serial RS485 output for make a multipoint temperature measuruing. All this measures are controlled in a host (PC or PLC).

This project, is for big installations of air conditionated in entire buildings.

I believe that now the subject is more clear.

Thanks

#### techie

the shematic practical termometer with lm335

Using an NTC theremistor is bar far the easiest and most accurate way to measure temperature in a cost sensitive application. Since the coefficient for NTC thermistor is the highest among all the prevailing temperature sensors, the demands on the measurement circuit is less. I have successfully used NTC thermistors for 0.01degF (yes better than 0.1degC) with just using a monostable like CD4538 and measuring the resultant pulse width to measure temperature. Ofcourse, without calibration, you are getting nowhere. The only problem with this arrangement is that you either have to use variable capacitors or do a software calibration on time measured.

#### BaGRoS

##### Newbie level 6
what is the best way to measure air temperature

marcosax said:
You can use LM92 from national or Dallas/maxim DS18B20
+/-0.5C

You possess in VisualBasic examples to service how on:
??

#### tmk

##### Newbie level 6

I realized a ON/OFF control project for temperature. I made it at unniversity. Maybe it can help you. The sensor is LM35DZ. it measures 0..+100 C degree. yuo can use another sensor for this. I attached the protel database file and C source code for this and all of them is free.

Maybe it can give an idea for control tecniques and implementation. but I don't the library files and i used Bytecraft C complier for PIC.

tmk 8)

#### Fragrance

kty10 temp probe

tmk said:
I realized a ON/OFF control project for temperature. I made it at unniversity. Maybe it can help you. The sensor is LM35DZ. it measures 0..+100 C degree. yuo can use another sensor for this. I attached the P*otel database file and C source code for this and all of them is free.

Maybe it can give an idea for control tecniques and implementation. but I don't the library files and i used Bytecraft C complier for PIC.

tmk 8)

great full for your contribution but i do not have protel99se could you please made jpg or pdf for the schematic

cd4538

exported sch

pool_77

#### is_razi

##### Full Member level 3
pt100 pic maxim ds1820

dear tranki,
you can use the "AD7711A" from analog device company.
this ic is specially developed for RTD's.
it has onchip current source for rtd ,adc, serial interface,...
i think this will solve your problem.
good luck. 8) 8) :idea:

#### artem

lm35dz pdf

There is "Low-Cost Digital Thermometer Uses Single-Chip Microcontroller" paper is available at :

MSP430F412 mcu with source code included
sensor - thermistor .

#### Humber555

##### Member level 2
ysi44031

Well, I need measure air conditioned installations.

The range of temperatures is about -30ºC to +40ºC. The reason of precission is the problem. I find many information on IC's and schematic circuits for temperature measure, but I need a precision of 0.2ºC because the system uses diferential temperature between ambient and flow air conditioned temperature

Hi Tranki,

For these temperature span and resolution you will need a 12bit ADC.
I had the finished product you are looking for, it has the capability of 32
remotes with 4 Analog Channels each.
It collect full 128 temperatures measurements and shows them in a windows screen once a second.
Also has the capability to handle remote relays for switch-on / switch-off according to setting points.

If you are interested just let me know.

humber555

#### Humber555

##### Member level 2
lm92 timing software in c

Well, I need measure air conditioned installations.

The range of temperatures is about -30ºC to +40ºC. The reason of precission is the problem. I find many information on IC's and schematic circuits for temperature measure, but I need a precision of 0.2ºC because the system uses diferential temperature between ambient and flow air conditioned temperature

Hi Tranki,

For these temperature span and resolution you will need a 12bit ADC.
I had the finished product you are looking for, it has the capability of 32
remotes with 4 Analog Channels each.
It collect full 128 temperatures measurements and shows them in a windows screen once a second.
Also has the capability to handle remote relays for switch-on / switch-off according to setting points.

If you are interested just let me know.

humber555

#### mgajo

##### Full Member level 2
measure temperature use ntc pic

Hi
I am using DS18b20 with 8051

Resolution 0.0625 C

Wire lenght 30m

Status
Not open for further replies.