Author Topic: MAX31855 temperature error (reads 25% low)  (Read 20573 times)

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Offline David_AVD

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Re: MAX31855 temperature error (reads 25% low)
« Reply #25 on: May 21, 2014, 05:10:18 pm »
Sample from Maxim?

That would take weeks.  I'll get a breakout board from Wiltronics in the mean time as I need to get this prototype running ASAP.
 

Offline Tinkerer

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Re: MAX31855 temperature error (reads 25% low)
« Reply #26 on: May 21, 2014, 10:31:42 pm »
It really does look like the chip is the wrong curve.

I bought the chips from Digikey; 2 pieces originally then another 2 a month later.  The two prototypes have one from each purchase, but they are probably the same batch.

Unfortunately neither RS or Farnell have stock, so can't easily get another chip to see if that's the issue.   :(

I'll see if I can get one somewhere else and go from there.
I have heard that Digikey will substitute 'equivalent' parts when they can if what they sold isnt actually in stock(and without telling you; happened to my company a few times). Are you sure the chip you ordered and the chip you got are the same?(obvious question, I know)
 

Offline free_electron

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Re: MAX31855 temperature error (reads 25% low)
« Reply #27 on: May 22, 2014, 03:16:24 am »
boiling water ? water is conductive.... make sure you have a thermcouple that is fully electrically isolated ...
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Any comments, or points of view expressed, are my own and not endorsed , induced or compensated by my employer(s).
 

Offline CrabxCore

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Re: MAX31855 temperature error (reads 25% low)
« Reply #28 on: May 22, 2014, 04:25:13 am »
Sample from Maxim?

That would take weeks.  I'll get a breakout board from Wiltronics in the mean time as I need to get this prototype running ASAP.

This is how I got my 2 chips for my project. They shipped from the philippines to the USA in about a week. Much faster than what I was expecting!
 

Offline mg326

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Re: MAX31855 temperature error (reads 25% low)
« Reply #29 on: May 22, 2014, 04:54:50 am »
Hi David_AVD,

I have been using the MAX31855 in a project and have produced a number of prototype boards using it and have had no problems up until this point. I have just however produced a new batch of these boards and am seeing the exact same problem you have described on 75% of them (i.e. reading ~78°C at 100°C input from an Omega thermocouple calibration unit). The new board has some very minor alterations from previous versions, none of which should be relevant to this behaviour from the MAX31855.

If you make any progress with finding out whats going on, please post it up as it would be hugely helpful to me too, but from my perspective it definitely looks like a problem with the component itself.
 

Offline amyk

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Re: MAX31855 temperature error (reads 25% low)
« Reply #30 on: May 22, 2014, 06:07:27 am »
We now have 2 reports of MAX31855s behaving wrongly in the same way, so a mismarked batch seems likely.
 

Offline David_AVD

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Re: MAX31855 temperature error (reads 25% low)
« Reply #31 on: May 22, 2014, 06:45:38 am »
boiling water ? water is conductive.... make sure you have a thermcouple that is fully electrically isolated ...
Yes, the thermocouple is fully isolated and suitable for liquid immersion.   :)
 

Offline David_AVD

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Re: MAX31855 temperature error (reads 25% low)
« Reply #32 on: May 22, 2014, 06:48:23 am »
I have been using the MAX31855 in a project and have produced a number of prototype boards using it and have had no problems up until this point. I have just however produced a new batch of these boards and am seeing the exact same problem you have described on 75% of them (i.e. reading ~78°C at 100°C input from an Omega thermocouple calibration unit). The new board has some very minor alterations from previous versions, none of which should be relevant to this behaviour from the MAX31855.

Interesting.  I've wasted way too much time on what should have been such a simple circuit.  I'll update here once I get another chip.

EDIT: I've emailed Maxim support to see what they say.
« Last Edit: May 22, 2014, 07:11:18 am by David_AVD »
 

Offline mg326

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Re: MAX31855 temperature error (reads 25% low)
« Reply #33 on: May 22, 2014, 10:23:55 pm »
Have just had confirmation from MAXIM that it was a faulty batch, the affect chips are:

Date Code: 1352A2
Lot Code: 253AL
 

Offline David_AVD

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Re: MAX31855 temperature error (reads 25% low)
« Reply #34 on: May 23, 2014, 06:55:17 am »
That batch is what two of the chips I have are.  I *think* the other two were different, but will double check when I get into work.
 

Offline David_AVD

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Re: MAX31855 temperature error (reads 25% low)
« Reply #35 on: May 23, 2014, 01:25:40 pm »
Just checked the other prototype and it has batch:
Date code: 1435A2
Lot code:  253AK

Both batches of chips are giving me the same result, so maybe there is more than one bad batch ?

Maxim did reply to my enquiry, but only to say they are looking into it and will reply again ASAP.
 

Offline David_AVD

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Re: MAX31855 temperature error (reads 25% low)
« Reply #36 on: May 27, 2014, 07:20:56 am »
Just got word from Maxim:

Quote
Replacement parts should not be from lots ending in either "253" or "107"
 

Offline David_AVD

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Re: MAX31855 temperature error (reads 25% low)
« Reply #37 on: May 30, 2014, 03:26:17 pm »
Well, Digikey sent me 2 replacement chips as soon as I verified when I purchased them.  They arrived today and they are batch code 107AE.

I wasn't confident that they would be any better than the 253xx batch, but just replaced the chip in both prototypes and the temperature is spot on.  Whoo!

So, not entirely sure what to make of Maxim's email saying the 107xx batch are also bad.  The 253xx batch do seem to have been proven bad of course.
 

Offline dannyf

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Re: MAX31855 temperature error (reads 25% low)
« Reply #38 on: May 30, 2014, 08:27:22 pm »
Quote
not entirely sure what to make of Maxim's email saying the 107xx batch are also bad.

Maxim has poor documentation of its production process? That's scary.
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Offline amyk

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Re: MAX31855 temperature error (reads 25% low)
« Reply #39 on: May 30, 2014, 10:06:35 pm »
They probably mean that some of the 107xx batch could be bad, and they're not sure exactly which ones, so to be safe they're saying to avoid the whole batch.
 

Offline David_AVD

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Re: MAX31855 temperature error (reads 25% low)
« Reply #40 on: May 30, 2014, 10:16:38 pm »
Still somewhat annoyed at the (unchargeable) wasted hours on this project due to something out of my control and should never happened.   >:(
 

Offline dannyf

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Re: MAX31855 temperature error (reads 25% low)
« Reply #41 on: May 30, 2014, 11:43:13 pm »
Quote
they're not sure exactly which ones,

That is not tolerable for production purposes.
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Offline 48X24X48X

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Re: MAX31855 temperature error (reads 25% low)
« Reply #42 on: June 12, 2014, 03:44:14 pm »
Hi guys,

I experienced the same problem of the same batch of the MAX31855KASA+ bought from Mouser.
It's painful because I already shipped a handful of them to customer.  |O

In my case, the differences of reading started to show more when the temperature goes up higher.
I got a toasted PCB as a result. Now, I'm wondering whether Maxim did a random test on each batch.
 

Offline 48X24X48X

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Re: MAX31855 temperature error (reads 25% low)
« Reply #43 on: June 12, 2014, 07:37:51 pm »
Quote
So it looks like the trim issue is only on MAX31855KASA+ units with lot codes 253AL and 253AK with date code 1352A2. I also notice that data code 1345 is also with the same issue. other data code should be ok.

That is the reply from Maxim.
No apologies given by them on top of that.
 


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