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Increasing the sample rate MAX31850
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Increasing the sample rate MAX31850

by Nikxy on Fri May 30, 2014 11:22 am

Hi,
i am using the one wire thermocouple amplifier MAX31850 on Arduino UNO for logging the exhaust gas temperature.
Can i increase the sample rate up to 10 S/sec. The current sample rate is about 1 S/sec @ 12 bit resolution.
The attempt to reduce the resolution (it will be faster in communication) to 9 bit ( by #define TEMPERATURE_PRECISION 9) was not successful.
Because the device is still in 12 bit modus.. I don´t know why...
Used test sketch: DallasTemp --> Multiple (with include OneWire.h & DallasTemperature.h)

Thx and Best Regards,

Nikxy
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Re: Increasing the sample rate MAX31850

by adafruit_support_rick on Sat May 31, 2014 12:53 pm

I see nothing in the data sheet about changing the resolution. It's fixed at 14 bits.
And the sample rate is what it is - it's mostly governed by how fast you can transfer data over one-wire.

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Re: Increasing the sample rate MAX31850

by Jericho730 on Fri Aug 08, 2014 8:20 pm

I’m having a similar issue. I don’t care much about the speed, I’m just curious. The function

sensors.setResolution(insideThermometer, 9);

from the Max31850_Dallastemp single example sketch does not seem to work with this chip. After sending the above code the example sketch then runs these lines of code.

Serial.print("Device 0 Resolution: ");
Serial.print(sensors.getResolution(insideThermometer), DEC);
Serial.println();


Pretty simple right? One would think the result of getResolution would be whatever you set it to in the first line of code. However, no matter what you set it to, 12 is returned. As you mentioned the resolution on the data sheet says 14. So why is 14 not being returned? Even if you do

sensors.setResolution(insideThermometer, 14);

12 is still returned.

I don’t think I have any wiring issues because everything works perfectly in terms of getting temperatures and the temps are within a degree of my calibrated thermometer. I couldn’t get this to work in my own sketch so I went back to the unmodified example sketch mentioned above. The getResolution returns 12 every time on all 4 of the Max31850 1 wire amplifiers that I have purchased from you guys.

Once again I’m not complaining and I’m perfectly happy with the product just curious and trying to learn.

Thank you.

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Re: Increasing the sample rate MAX31850

by Jericho730 on Fri Aug 08, 2014 8:33 pm

Found this in the library but why?
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Re: Increasing the sample rate MAX31850

by Franklin97355 on Fri Aug 08, 2014 9:44 pm

The code was originally written for the DS18x20 chip and on those you can change the resolution from 9 to 12 at the cost of slower response times. In this case it is just an artifact.

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Re: Increasing the sample rate MAX31850

by Sasanesmaili on Tue Jun 30, 2015 4:50 pm

I have amax31850 thermometer and I used it by Arduino but when I measure the temperature of Liquid nitrogen (normally -200 Celsius) it show -140 Celsius
Can you tell me what is problem ? because I spot welded K type Thermocouple and I want measuring very low temperature -250 Celsuis by Max31850

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Re: Increasing the sample rate MAX31850

by adafruit_support_bill on Tue Jun 30, 2015 5:02 pm

K-type thermocouples are not linear at that temperature and require linearization. Linearizing the 31850 should be similar to the 31855:
https://learn.adafruit.com/calibrating- ... earization

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Re: Increasing the sample rate MAX31850

by Sasanesmaili on Tue Jun 30, 2015 5:16 pm

@ adafruit_support_bill many thanks for your quick response Can I use the same code for 31850 or I have to change something ? please let me know because my PhD priject stooped for this reason.

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Re: Increasing the sample rate MAX31850

by adafruit_support_bill on Tue Jun 30, 2015 6:07 pm

The linearization calculation would be the same. Unfortunately, the "Dallas" temperature library does not appear to have support for reading the cold-junction temperature on this device. So I'm afraid it won't work.

Would it be possible to switch to the MAX31855? https://www.adafruit.com/product/269
That has full support for reading the cold junction temperature.

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Re: Increasing the sample rate MAX31850

by Sasanesmaili on Tue Jun 30, 2015 6:22 pm

it's possible but unfortunate the temperature range for Max3155K is -200°C to +1350°C and I have to measure -250 Celsuis .
Is that possible by Max3155K ?

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Re: Increasing the sample rate MAX31850

by adafruit_support_bill on Tue Jun 30, 2015 6:50 pm

According to the datasheet, it goes down to -270C also:
http://www.adafruit.com/datasheets/MAX31855.pdf

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Re: Increasing the sample rate MAX31850

by Sasanesmaili on Tue Jun 30, 2015 6:53 pm

Thanks , So I will switch to use that with that calculation you mentioned If I had more question can I ask you latter ? :)

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Re: Increasing the sample rate MAX31850

by adafruit_support_bill on Tue Jun 30, 2015 6:54 pm

Absolutely. You can post any questions here on the forum.

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Re: Increasing the sample rate MAX31850

by Sasanesmaili on Fri Jul 10, 2015 9:45 am

Finally I switched to Max31855 but now I should copy the code that is in following link :
https://learn.adafruit.com/calibrating- ... earization
corrected temperature reading for a K-type thermocouple or I have to add this code to main Max31855 library ?
please provide me how can I upload the corrected code on my Arduino I try but failed

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Re: Increasing the sample rate MAX31850

by adafruit_support_bill on Fri Jul 10, 2015 3:32 pm

You add that function to your sketch and call it with the raw reading from the MAX31855 to perform the linearization.

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