PT100 amplifier board - redaings seems to be 30 degrees below

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?

dc42

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

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”?

Yes.

tony449777

@dc42 yes

tony449777

@dc42 I’m using the phone application. Every time I try to attach a picture it just says undefined.

dc42

@tony449777 it's easier from a PC, you can just drag and drop a .jpg file into your post.

tony449777

@dc42 Update. Switched out the daughter board for another one I purchased from filastruder and it works fine. It must be the board.

Phaedrux

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

I believe I got this daughterboard from Filastruder. It was purchased a while ago, but never used until this build.

How long is a while ago?

c310

@dc42 my 2nd channel died :I( i will be replaceing the chip, on the way want to check other parts. there are 2 pairs of capacitors - c1/c2 + c5/c6 what its default capacity should be?

also there is small black SMD element in between C1 and R1. what is it? what are the parameters?

many thanks!