MAX31865 & PT100 no work

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barshnik
 
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MAX31865 & PT100 no work

Post by barshnik »

Quite sure its all wired correctly. One thing that bothers me is that the 3-wire sensor measures .5 ohm instead of 2 ohm as the docs say it should. Between reds and blue leads reads 110 ohm instead of 100 indicated in the docs. Help please. Here is what I'm getting on the serial monitor. Please help, very frustrated.

RTD value: 32767
Ratio = 0.99996948
Resistance = 429.98687744
Temperature = 988.79
Fault 0xFF
RTD High Threshold
RTD Low Threshold
REFIN- > 0.85 x Bias
REFIN- < 0.85 x Bias - FORCE- open
RTDIN- < 0.85 x Bias - FORCE- open
Under/Over voltage

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barshnik
 
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Re: MAX31865 & PT100 no work

Post by barshnik »

Hmm, just disconnected the 3 wire sensor and get exact same monitor response. Does it think the reds (measuring just under .4 ohm instead of 2 ohms) are 'open'? Bad sensor? Thanks,

John F

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barshnik
 
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Re: MAX31865 & PT100 no work

Post by barshnik »

Resistance between either red and single blue changes from 110 ohm to 130 after a second from a lighter, so sensor likely good? Bad board?

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adafruit_support_mike
 
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Re: MAX31865 & PT100 no work

Post by adafruit_support_mike »

Post a photo showing your hardware and connections and we'll take a look. 800x600 images usually work best.

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barshnik
 
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Re: MAX31865 & PT100 no work

Post by barshnik »

The solder blobs (although a little sloppy) check out good for 3 wire with the Fluke. I sure hope you see something stupid, if not it appears the board may have a problem, no? It and the sensor are new from you. Any troubleshooting tips before giving up on it?
Attachments
MAX31865.jpg
MAX31865.jpg (154.96 KiB) Viewed 4643 times

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adafruit_support_mike
 
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Re: MAX31865 & PT100 no work

Post by adafruit_support_mike »

The soldering along all the pins looks good.

Are you sure the trace to the pad marked '24' has been cut, and isn't bridged by solder? Things look a little tight in that region.

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barshnik
 
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Re: MAX31865 & PT100 no work

Post by barshnik »

Yep, the bridge is definitely cut, have triple checked with needle tips. I get identical serial monitor response whether the sensor is connected or not. At least the reference resistor is meeting specs! Any other ideas? Is it possible to get a replacement, or?? I appreciate you help.

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adafruit_support_mike
 
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Re: MAX31865 & PT100 no work

Post by adafruit_support_mike »

Actually, I just looked closer at the rest of the board and there's a part missing.. a diode near the 3v3 pin.

That counts as a production defect. Send a note containing a link to this thread and your order number to [email protected]. The folks there will get you a replacement.


(#3328)

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barshnik
 
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Re: MAX31865 & PT100 no work

Post by barshnik »

Thanks Mike - you've helped relieve a good deal of frustration. Good eye...

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arduinoprogrammer
 
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Re: MAX31865 & PT100 no work

Post by arduinoprogrammer »

Hi,

Good afternoon everyone ,I'm working on this max31865 & 3 wire PT 100 in document and in the comments below everyone is telling 2 modifications for the board one is soldering 2/3 wire jumper and 24 3 jumper do I need to cut the small copper bridge joining '24' joining 3 or should I just solder 3 without cutting the bridge can someone clearly explain what needs to be done at tat area so that I can work with 3 wire PT100
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max 31865 24 3 jumper
max 31865 24 3 jumper
24 3 jumper.jpg (6.51 KiB) Viewed 4387 times

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misham
 
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Re: MAX31865 & PT100 no work

Post by misham »

I have the exact same problem with the exact same error.

I attached the image of it wired up. I'm using the Arduino library but on a Photon.

I did check to make sure that the pads that need to be cut are actually cut.

There is a bunch of flux around the pads cause I removed the solder and re-bridged them to make sure it was good.
Attachments
1.png
1.png (866.8 KiB) Viewed 4219 times

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zcox
 
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Re: MAX31865 & PT100 no work

Post by zcox »

I think I'm having the same problem. I am unable to read any data from the MAX31865 that makes any sense, using https://github.com/zcox/MAX31865 with a Raspberry Pi 3. I always see output like this:

Code: Select all

pi@raspberrypi:~/MAX31865 $ python ./max31865.py
config register byte: ff
RTD ADC Code: 32767
PT100 Resistance: 429.986877 ohms
Straight Line Approx. Temp: 767.968750 degC
Callendar-Van Dusen Temp (degC > 0): 988.792111 degC
high fault threshold: 32767
low fault threshold: 32767
pi@raspberrypi:~/MAX31865 $ python ./max31865.py
config register byte: 0
RTD ADC Code: 0
PT100 Resistance: 0.000000 ohms
Straight Line Approx. Temp: -256.000000 degC
Callendar-Van Dusen Temp (degC > 0): -246.861024 degC
high fault threshold: 0
low fault threshold: 0
pi@raspberrypi:~/MAX31865 $ python ./max31865.py
config register byte: 0
RTD ADC Code: 0
PT100 Resistance: 0.000000 ohms
Straight Line Approx. Temp: -256.000000 degC
Callendar-Van Dusen Temp (degC > 0): -246.861024 degC
high fault threshold: 0
low fault threshold: 0
I verified the two jumpers are soldered/cut correctly for the 3-wire PT100 using a multimeter. I actually read the same values if I remove power to the MAX31865. Also verified it's getting 3.3V between VIN/GND. Any chance I'm missing that diode near 3V3 as well?
Attachments
00002IMG_00002_BURST20180318122605-01.jpeg
00002IMG_00002_BURST20180318122605-01.jpeg (779.62 KiB) Viewed 4177 times

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Shermit
 
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Re: MAX31865 & PT100 no work

Post by Shermit »

Hi ZCOX i'm having the same problem, did you find a solution?

faffine
 
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Re: MAX31865 & PT100 no work

Post by faffine »

same issue here, did you find a solution?

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