Thermisors showing wrong temperatures

mendelevium

I have the following configuration of my temperature sensors..

M308 S0 P"bedtemp" Y"thermistor" T100000 B4138 ; configure sensor 0 as thermistor on pin bedtemp
M950 H0 C"bedheat" T0 ; create bed heater output on bedheat and map it to sensor 0
M307 H0 B1 S1.00 ; enable bang-bang mode for the bed heater and set PWM limit
M140 H0 ; map heated bed to heater 0
M143 H0 S120 ; set temperature limit for heater 0 to 120C
M308 S1 P"e0temp" Y"thermistor" T100000 B4138 ; configure sensor 1 as thermistor on pin e0temp
M950 H1 C"e0heat" T1 ; create nozzle heater output on e0heat and map it to sensor 1
M307 H1 B0 S1.00 ; disable bang-bang mode for heater and set PWM limit
M143 H1 S280 ; set temperature limit for heater 1 to 280C
M308 S2 P"e1temp" Y"thermistor" T100000 B4138 ; configure sensor 2 as thermistor on pin e1temp
M950 H2 C"e1heat" T2 ; create nozzle heater output on e1heat and map it to sensor 2
M307 H2 B0 S1.00 ; disable bang-bang mode for heater and set PWM limit
M143 H2 S280 ; set temperature limit for heater 2 to 280C

First I got errors that temp is not reaching out...
i have found out that when temperature shows 235, the temp is actually around 35 degrees. I checked with a digital thermometer.
can some body help please
Thanks in advance
tonio

SIam

@mendelevium said in Thermisors showing wrong temperatures:

B4138

What kind of hotend respectively thermistor are you using?

dc42

@mendelevium said in Thermisors showing wrong temperatures:

i have found out that when temperature shows 235, the temp is actually around 35 degrees. I checked with a digital thermometer.

What sort of digital thermometer? IR thermometers are no good for measuring the temperatures of small surfaces such as nozzles.

mendelevium

@dc42
I have a food thermometer with a probe which I machined to go inside the heat-block and it reads the temperature very accurately. I am using very common thermocouples and they worked well when used over a ramps/arduino arrangement.

mendelevium

@siam
I have a common thermocouple which gave me very good readings when I used a ramps card.

mendelevium

@mendelevium
Good to mention that all the thermocouples are connected directly to the board with no expansion boards or daughterboards.

Dougal1957

@mendelevium said in Thermisors showing wrong temperatures:

@mendelevium
Good to mention that all the thermocouples are connected directly to the board with no expansion boards or daughterboards.

so some confusion now your title said thermistors but your now saying Thermocouples . Which is it as both operate differently?

dc42

@mendelevium, what do the thermistors read at room temperature?

mendelevium

@dc42
I have thermocouples sorry for the confusion my mistake
They do not read anything on the dashboard - Just N/A
but when the heaters were tested they read the temperature and maintain it but obviously they overread the temperature as it did not actually reach the temperature it displayed.

The digital thermometer I got to check the situation as the filament did not melt at the temperature the system displayed.

mendelevium

@dougal1957 - sorry they are thermocouples... my mistake as they are not the same thing sorry again...

Dougal1957

@mendelevium said in Thermisors showing wrong temperatures:

@dougal1957 - sorry they are thermocouples... my mistake as they are not the same thing sorry again...

in that case you need the Thermocouple daughter board as well!

mendelevium

@dougal1957
I have two thermocouples for the hotends and another for the heatbed which runs on 220V but has an enclosed unit. the daughterboard takes up the three of them?

mendelevium

@mendelevium
I have checked my purchases because I have bought the stuff months ago....
I should have a type K thermocouple daughterboard and a pt 100 daughterboard...
i have to look it up...

Dougal1957

@mendelevium said in Thermisors showing wrong temperatures:

@dougal1957
I have two thermocouples for the hotends and another for the heatbed which runs on 220V but has an enclosed unit. the daughterboard takes up the three of them?

Each daughter board takes unto 2 sensors but you can also stack 2 daughter boards to give your 4 sensors.

mendelevium

@mendelevium
I have found one daughter board and will buy another one. I have one issue though because my thermocouples were single wired to the board and used a common GND cable. Anybody knows if the daughterboard output have one terminal as a ground? otherwise I have go through much hassle...

mendelevium

@mendelevium

mendelevium

@dougal1957
I have rewired the thermocouples and fitted a Max 31856 daughterboard
I have the heatbed and Extruder 0 connected.

I have now changed the relevant parameters as follows;-

M308 S0 P"bedtemp" K"thermocouple-max31856"

M308 S1 P"e0temp" K"thermocouple-max31856"

its telling me unknown sensor

Dougal1957

@mendelevium said in Thermisors showing wrong temperatures:

@dougal1957
I have rewired the thermocouples and fitted a Max 31856 daughterboard
I have the heatbed and Extruder 0 connected.

I have now changed the relevant parameters as follows;-

M308 S0 P"bedtemp" K"thermocouple-max31856"

M308 S1 P"e0temp" K"thermocouple-max31856"

its telling me unknown sensor

do you definitely have one with the 31856 rather than the 31855?(seem's they changed at some time during the run)

You may have to wait for one of the crew to comment (I am by no means an expert on this)

droftarts

@mendelevium your command is wrong; they are not plugged into bedtemp and e0temp, they are plugged into spi.cs1 and spi.cs2. See https://duet3d.dozuki.com/Wiki/Connecting_thermocouples#Section_RepRapFirmware_3_x

Ian

mendelevium

@droftarts thanks so much...