PT100 amplifier board - redaings seems to be 30 degrees below

c310

Hi! please advise how to fix duet daughter board.

after changing few PT100 sensors it figured out that channel 1 of the amplifier board does not function correctly - reading are 30 degrees below .

checked it with 100 Ohm resistor and both channels needed adjustments
ch1 = R405
ch1 = R395

by my eye ch2 readings are much more accurate.

what can i test (and replace) on the daughter board?
thank you!

dc42

@c310 What does channel 1 read with the 100R resistor connected and no R adjustment?

The reference resistors on the PT100 board are R1 and R2. The specification is 400 ohms 0.1%, tolerance. If they really are 395 and 405 ohms, they are way out of tolerance. You can check them with a multimeter. Don't expect them to read exactly 400 ohms, because your multimeter is unlikely to be that accurate; but they should both read the same. Mine both read 398 ohms.

c310

@dc42 said in PT100 amplifier board - readings seems to be 30 degrees below:

pect them to read exactly 400 ohms, because your multimeter is unlikely to be that accurate; but they should both read the same. Mine both read 398 ohms.

direct measurements of R1 and R2 on the board are both around 399 ohms.

i removed all cables from the daughter board and connected same 100 ohm resistor

tested channel 1: M308 S1 P"spi.cs1" Y"rtd-max31865"
reads -2.8 degrees that within 1 minute fluctuated to -3.2 degrees

moved resistor and tested channel 2: M308 S1 P"spi.cs2" Y"rtd-max31865"
reads 0.8 degrees stable

which element could be deffective?

dc42

Do all the solder joints on that channel look good, especially the ones on the terminal block that you connect the sensor to?

Ty removing and refitting the two jumpers on that channel, assuming that you are using 2-wire mode.

How old is the daughter board? If it is less than a year old and we can't find a resolution, then I will approve a warranty replacement.

c310

@dc42
i have re-soldered all joints, cleaned the board and re-measured. it did not change.
from the board to smarteffector i have 4 cables running and they are in the grounded shield.

is there anything on the duetWiFi mainboard that can be damaged? if not...
board is more than a year old, so for now i will use channel 2, and replace board when it dies.... thanks!

dc42

@c310 if all the connections are OK then unless there is some contamination on the board (e.g. condensation or soldering flux), I guess the next thing would be to replace the MAX31865 chip. But if the second channel is free, just use that.

c310

@dc42 thank you very much for support!

tony449777

I am also having a similar problem. I printed one day with my printer and noticed that the temperature trajectory bounced around a lot. Started to print the next day and noticed that after sitting all night and everything settling to room temperature there were major differences between my bed temperature and nozzle temperature. The bed uses a standard glass in cased thermocouple. I am using a PT 100 with daughter board for the hot end. I moved a 100ohm Resistor in place of the PT 100 cartridge and get a reading of -20c. It should’ve been zero.

Current code :
Y248)

; Heaters
M308 S0 P"bedtemp" Y"thermistor" A"bed_heat" T100000 B3950 R4700 H0 L0 ; configure sensor 0 as thermistor on pin bedtemp
M950 H0 C"bed_heat" T0 ; create bed heater output on bedheat and map it to sensor 0
M140 H0 ; Inform the firmware that bed heater 0 uses heater 0
M143 H0 S120 ; Set temperature limit for heater 0 to 120C
M308 S1 P"spi.cs1" Y"rtd-max31865" ; configure sensor 1 as thermistor on pin spi.cs1 (Hotend)
M950 H1 C"e0_heat" T1 ; create nozzle heater output on e0heat and map it to sensor 1
M143 H1 S320 ; Set temperature limit for heater 1 to 320C
;M308 S2 P"duex.e6temp" Y"thermistor" A"keenovo" T100000 B3950 R4700 C7.06E-8 H0 L0 ; Secondary bed thermistor
M140 S0 R0 ; Standby and initial Temp for bed set to 0 (-273 = "off")
M308 S10 Y"mcu-temp" A"mcu-temp" ; Display Duet2 CPU temp

Phaedrux

@tony449777 Can you check the values of the resistors as mentioned by DC42 above?

tony449777

@phaedrux

R1 200.2
R2 200.2/3

Phaedrux

@tony449777 They appear to be exactly half of what they should be...

tony449777

@phaedrux I wonder how that could happen? I believe I got this daughterboard from Filastruder. It was purchased a while ago, but never used until this build.

dc42

@tony449777 the multimeter may give the wrong (lower) resistance readings, depending on what voltage it uses to measure resistance. If it was previously working then the resistors should be OK.

tony449777

@dc42 I’m using a Fluke. I have 3 others. I’ll try them all. However, how would we ever be able to come up with a reference for resistors if all multimeters give us such a diverse readings?

tony449777

@dc42 I can’t attach a picture, it will not let me however I can tell you R1 is marked”102” while R2,R3,R4 are all marked “201”

tony449777

On my precision bench meter both resistors measure R1-199.50 and R2-199.52

tony449777

I also have 3 PT100 cartridges in the same room measuring within 1° of each other. By that I mean looking at a PT 100s resistance table and measuring each one’s resistance, according to the table they are within 1° of each other.

tony449777

Also curious, if the channel 1 on the daughter board is “spi.cs1”
And you have one daughter board with the two ports, then is the second port for the same card “spi.cs2”?

tony449777

This post is deleted!

dc42

@tony449777 said in PT100 amplifier board - redaings seems to be 30 degrees below:

@dc42 I can’t attach a picture, it will not let me however I can tell you R1 is marked”102” while R2,R3,R4 are all marked “201”

Why can't you attach a picture?

Do both channels give the wrong reading when you connect the 100 ohm resistor to each in turn?